home Citizenship of the Russian Federation Why is evolution on the islands faster? The island law sets the dimensions for underwater inhabitants in species of animals that are isolated on the islands.

Why is evolution on the islands faster? The island law sets the dimensions for underwater inhabitants in species of animals that are isolated on the islands.

POSITION

about the regional team ecological tournament

"Time Machine"

1. Goal and tasks

The goal is to involve students in research activities in the field of ecology.

- fostering a careful and humane attitude towards nature;

- the formation of students' ability to think logically, analyze and solve environmental problems;

– formation of environmental literacy.

2. Tournament Participants

Teams of students from educational organizations of municipal districts and city districts take part in the Tournament Nizhny Novgorod region. The number of team members is 6 people. Age of participants is from 14 to 18 years.

3. Tournament content

Teams present solutions to environmental tasks in the form of three presentations. The title page of each presentation should contain: last names, first names, patronymics and dates of birth of all authors, last name, first name and patronymic of the team leader, full name and address of the educational organization, contact phone number, e-mail.

Technical requirements for the presentation: number of slides 10-15, file format - .ppt or .pptx; the presence of media files (audio, video) and hyperlinks. The executable file must run under the Windows XP operating system.

Tasks for the Tournament:

1. "The ark". In 2526, a star system was discovered in the M13 galaxy, in which one of the planets turned out to be very similar to Earth in most parameters, but it completely lacked any signs of life. It was decided to colonize this planet. People can equip only one ship for this mission, the number of places on which is very limited. You need to draw up a minimum list of species of living beings that will be transported to the planet. What considerations will you be guided by? Will these species be enough to create a biosphere on a planet being developed?
2. "Kingdom of Hades". For animals - roglobionts, caves are a permanent habitat. What ecological and physiological adaptations are necessary for a vertebrate to become a permanent inhabitant of caves? Guess which order of vertebrates that do not currently live in caves would be most likely to become troglobionts and indicate the signs that will allow them to switch to this way of life.

3. "Alice on the island". In animal species isolated on the islands, in the course of evolution, changes in body size often occur, both upwards (the giant Maltese swan) and downwards (the pygmy Maltese elephant). What factors predict whether an organism will grow or shrink in the course of such evolution? What other terrestrial and aquatic biotopes show a similar evolutionary effect? Why does this effect most often extend to animals and not to other living organisms?

4. Procedure and terms of the Tournament

4.1. The tournament is held in two stages:

Qualifying;

4.2. Tournament dates:

Istage(qualifying): February 2018. Takes place in GBUDO CRTD NO.

To participate in the Tournament, the organizing committee created by the body exercising management in the field of education municipal district and city district, before March 1, 2018 sends to e-mail This e-mail address is being protected from spambots. You must have JavaScript enabled to view. (GBUDO TsRTDIYU NO, department environmental education and education) application (Appendix 1), consent to the processing of personal data of a minor (Appendix 2), consent to the non-commercial use of competitive works (Appendix 3) and presentations of teams.

Based on the results of an expert assessment of the content of the presentations, the composition of the participants of the II stage of 9 teams is formed. Until March 28, 2018, an invitation to participate in the II stage of the Tournament is sent to the educational organizations whose teams have passed the qualifying stage.

4.3. The final of the Tournament is held in three rounds:

The first team presents the solution of one environmental task in the form of a short illustrated report (the time of the report is 5-7 minutes);

The second team plays the role of an opponent (subjects to a critical assessment of the completeness, correctness and validity of the presented decision of the opposing team);

The third team acts as a reviewer (observes the progress of the discussion and makes a conclusion about how well the other two teams coped with their roles).

In the next rounds, the teams change roles and play the following tasks.

The captain leads the team.

All actions of the team members are evaluated by the jury.

5. Summing up and awarding

Based on the results of the Tournament, the following are awarded:

In the final with diplomas, the team is the winner (1st place), the teams are prize-winners (2nd and 3rd places).

All teams have a certificate of participation.

___________________________

APPENDIX 1

to the regulation on the regional

team ecological tournament

"Time Machine"

Request

for participation in the regional team ecological tournament "Time Machine"

(body exercising management in the field of education of a municipal district, city district)

The person responsible for organizing and holding the regional team ecological tournament "Time Machine" in the municipal district / city district (full name, position, contact phone number), ________________________________________________________________________________________________________________________

APPENDIX 2

to the regulation on the regional command environmental

Tournament "Time Machine"

Consent to the processing of personal data of a minor

I AM,________________________________________________________________,

(last name, first name, patronymic - mother, father, guardian, etc.)

residing at ______________________________________________

place of registration _________________________________________________

name of the identity document: _____________, series ________ number ______________ issued by _______________________________

date of issue _____________, I express my consent to the processing of personal data _____________________________________________,

(last name, first name, patronymic, date of birth of a minor), whose legal representative I am, as well as my following personal data: last name, first name, patronymic, year, month, date, place of birth, registration address, passport data (hereinafter referred to as personal data ) GBU DO "Center for the Development of Creativity for Children and Youth of the Nizhny Novgorod Region"(hereinafter referred to as the Center), for registration of all required documents required in the process of holding the regional team ecological tournament "Time Machine" (hereinafter referred to as the Tournament), as well as subsequent events associated with the Tournament, taking into account the current legislation.

In case of misuse of my provided and personal data of the person, whose official representative I am, I reserve the right to withdraw my consent by submitting a written application to the Center.

The study of lizards in Brazil on the islands formed during the creation of the reservoir showed that the processes predicted in this case by evolutionary ecology can occur very quickly. In just a few years, some species of lizards became extinct, and one of the remaining ones, the bare-toed gecko Gymnodactylus amarali, having got out of the pressure of competitors, began to include larger prey in his diet. At the same time, the relative head size of island geckos increased, which can be explained by selection for more efficient hunting of large termites. These changes occurred independently of each other in all studied populations of islands isolated from each other.

Although many people associate evolution with slow changes lasting thousands and millions of years, in recent decades, biologists have also become aware of many examples of rapid evolution, both in experiment and in nature. The division into the so-called ecological and evolutionary time has gone down in history. Previously, biologists believed that on time scales measured in years or even centuries, the possible evolutionary response of organisms to changes in the environment could be neglected. The “ecological time”, during which the population actually remained unchanged, adapting to new conditions without the participation of natural selection, was opposed to a longer “evolutionary time”, during which the population cannot be considered as unchanged.

In particular, the classical models describing the relationship of populations - predation or competition - do not take into account the possible co-evolution. Now, rapid evolution is considered as one of the ways to adapt populations to constantly changing conditions (see Evolutionary and ecological processes can occur equally quickly and influence each other, "Elements", 08.02.2011). How significant these cases of direct observation of evolution are are also indicated by the fact that even creationists now recognize microevolution - changes in organisms that do not go beyond species boundaries (understanding them quite broadly, but this, as they say, is a completely different story).

Often such rapid evolution is provoked by anthropogenic changes in the environment. Here we can recall the first case of direct observation of the action of natural selection. At the end of the 19th century, the English evolutionary biologist W. F. R. Weldon published the results of his many years of research on crabs. Carcinus maenas in Plymouth harbor. He found that after the construction of the pier, the average width of the cephalothorax of crabs began to gradually decrease. It turned out that because of the pier, the harbor began to silt up, and the silt was constantly rising into the water column by the propellers of the ships. "Wide" crabs suffer more from gill contamination with silt. Because of this, their mortality became higher than that of the "narrow", which led to a gradual change in morphology in this population (see J. A. Harris, 1911.).

In evolutionary ecology, the processes that occur with animal species that come from large land masses to islands are well studied. Isolation and reduction of the available territory causes the extinction of some species, but at the same time, the ecological niches of those remaining due to the loss of competitors expand. But these conclusions are based mostly on a comparison of modern faunas, without observing the dynamics of the process.

The American-Brazilian group of scientists, which includes Thomas W. Schoener - the author of the article discussed in the above-mentioned news by Alexei Gilyarov - managed to see the initial stage of the change in the morphology of geckos caused by the formation of islands on the site of a previously single territory. In 1996, a dam was built in the Brazilian state of Goiás for the hydroelectric Serra da Mesa. From 1996 to 1998, 170,000 hectares of the South American cerrado savannah, one of the world's centers of biodiversity, were flooded. The former highlands have turned into 290 islands, on which parts of the original ecosystem have been preserved. As expected, many of their species died out - in particular, large lizards, which required a large territory. 15 years later, in 2011, the termite-eating bare-toed gecko became the most common lizard species on the newly formed islands. Gymnodactylus amarali(Fig. 1). The researchers focused their attention on it, collecting data on its diet and size.

According to the hypothesis of the authors, after the weakening of competition, these lizards should have expanded their food spectrum at the expense of larger termites, which should have led to an increase in the size of their heads. The authors considered the transition to other food in these specialized animals unlikely (all species of bare-toed geckos feed almost exclusively on termites), but the inclusion of larger prey in the diet should have been supported by selection, as this contributes to the rapid acquisition of the necessary nutrients and energy. Enlarging the head, rather than the whole body, would allow increasing energy consumption without a significant increase in needs - otherwise there could be no gain from the consumption of large insects. In addition, four of the six extinct on the islands (but preserved on big land) species of lizards that fed on termites were larger than Gymnodactylus amarali, and thus consumed larger termites. Thus, after their extinction, large termites should have become more accessible. (Another two extinct species fed on spiders and orthoptera.)

In 2011, the authors collected geckos on five islands (one of them periodically connected with the mainland, while the rest finally lost contact in 1998) and five nearest points on the coast of the reservoir (Fig. 2).

The contents of the stomachs of the captured lizards were studied in detail, determining the size of all the termites they ate. As a measure of the breadth of the ecological niche in terms of prey size, the authors used the inverse Simpson diversity index (Inverse Simpson index):

Here pi- share of each n size classes of eaten termites. This index changes from 1 to n, and the larger it is, the more varied the diet of geckos. The analysis included data from only three islands and three points on the mainland, since too few termites were found in the stomachs of lizards caught in the other four places.

As it turned out, the average diversity of diets in island populations is indeed somewhat higher than in lizards from the mainland: 3.74 versus 2.38. However, whether this difference is significant is an open question: in this case, there is some “statistical cunning” in the article. Is the difference found significant or not (see Statistical Significance)? The authors seem to claim that yes, citing R-value 3.3%. Recall that in this case R-meaning ( R-value) is the probability of random occurrence (due to bad sampling of geckos) of the same or even greater differences in the averages, provided that the latitude of niches on the islands and on the mainland is actually the same (this can happen because the averages in several samples from the same group will most likely differ - for example, the average height of several samples of classmates will vary from sample to sample). In biology (as well as in most other sciences that use mathematical statistics), an indication of the real existence of differences between two sets of values (which are examined on the basis of a sample of data from each set) is R-value less than 5%.

But in this case, the authors applied a one-sided test that calculates this probability based on the assumption that the difference, if any, is only in one of the directions. Such criteria should not be applied unless you obviously do not expect deviations in one of the directions (it is rather difficult to give adequate examples, but, for example, if you compare the height of young men and adults, then you can not expect it to decrease with age). And although the authors did not predict a possible decrease in the breadth of the diet on the islands (and this is how they explain the choice of a one-sided criterion - despite the fact that in all other cases they use two-sided ones), this possibility cannot be immediately rejected (for more details on one- and two-tailed criteria, see below). One-tailed vs. two-tailed P-values). Apparently they chose this test because the more appropriate two-tailed test gives R-value 6.6%, which is above the critical level of significance.

Nevertheless, I will give several arguments in defense of the assertion of the authors of the article. It can be seen from the table in the article that the smallest average niche latitude on the islands is greater than the largest in coastal populations (3.160 versus 2.917). In addition, “God loves 0.06 almost as much as 0.05” (famous quote describing the convention of the chosen critical level, from the article R. Rosnow, R. Rosenthal, 1989. Statistical procedures and the justification of knowledge in psychological science), and there is now a trend to use a smoother scale of significance rather than a strict separation along the 5% boundary. Last but not least, this is due to the fact that many researchers who do not understand the basics of statistics seek by hook or by crook to get the coveted " p < 5%» (это называют p-hacking, см. Data dredging). В данном случае 6,6% указывает на так называемую «краевую значимость». Отметим, что отец-основатель биологической статистики Рональд Фишер (Ronald Fisher) сам призывал использовать плавную шкалу.

Fortunately, the other results of the article are better substantiated. As it turned out, at the same size (measured as the length from the tip of the nose to the cloaca - the tail, as too variable, is traditionally not taken into account when measuring the length of lizards), island geckos consumed larger termites (Fig. 3, A), and their heads were relatively larger (Fig. 3c, head size was determined as the distance from the tip of the nose to the tympanic membrane). Note that from the graph in Fig. Figure 3 shows that in island geckos, the average size of termites eaten often exceeds that of coastal geckos - which again suggests that they have indeed expanded their diet. In addition, the head size of individual lizards appears to be positively correlated with the average size of termites in their diet.

Even more clear are the results not for individual individuals, but for the deviation of the ratio of head length to body length from the average value in individual populations (Fig. 4): it can be seen that this ratio is lower in all coastal populations than in all island populations. At the same time, the population of island IX, which periodically connects with the mainland, is closest to the coastal ones, and, accordingly, geckos on it could collide with competitors and interbreed with representatives of the coastal population.

Thus, isolation seems to have indeed led to an expansion in the size range of prey consumed by geckos. This caused their evolutionary response in the form of a change in morphology - an increase in the relative size of the head - which allowed them to more efficiently consume the large termites that became available. It is important that at the same time they have not lost the ability to eat small ones. And although island geckos should prefer to feed on large prey (this preference will again be supported by selection, as it increases the efficiency of hunting), the diet in a short time, which reflects the contents of the stomach, can be "small-sized" in some individuals. This is also seen from Fig. 3A: Small lizards do not prey on large termites (probably because they cannot do so efficiently), while large ones eat termites of all sizes.

What could be alternative explanations for the observed changes? First, it can be assumed that lizards had differences in head sizes even before the formation of the reservoir. However, this is unlikely: at that time they belonged to a single large population. In addition, a study of specimens caught on future islands and the mainland from 1996 to 1998 did not show any significant differences ( R= 0.68). Secondly, sexual selection could play a role here: due to the increased population density on the islands, the competition of males for females intensified, which could lead to an increase in head sizes. However, no relationship between the studied traits and sex was found in this study.

So, in the work under discussion, another example of rapid evolution is given: in just 15 years, lizards on the islands have adapted to the disappearance of competitors in eating termites. Moreover, these changes occurred in parallel to different islands: as they formed, the lizards on them lost contact with populations isolated on other islands. Cases of parallel evolution - independent acquisition of similar traits by related groups - suggest that in many cases evolutionary paths can be predictable. This result also contradicts the previously established (although not always strictly justified) ideas about the fundamental unpredictability of the results of natural selection (see news Cichlids - a living model of independent parallel evolution, "Elements", 11/14/2012 and Evolution of ants on "sky islands" Arizona turned out to be somewhat predictable, Elements, 09/16/2015).

However, if the studied geckos were able to adapt to changes in such a short time, why did other species of lizards still become extinct? Due to insufficient adaptation speed or because of something else? The study of such cases is necessary for a more complete understanding of how human activity will affect the biosphere. In addition, this will allow us to better understand the patterns of evolution and test hypotheses about how populations will respond to certain impacts - for this, as it turns out, it is not necessary to wait millions of years.

Oceanic islands have never been connected to land, they rose from the bottom of the ocean. "These include coral volcanic islands and islands of folded arcs. Continental islands are parts of continents that separated from them in one or another geological epoch. Naturally, the conditions for the development of biota on these or other islands are sharply different.

The mainland islands separated from the continent along with the totality of living organisms that were characteristic of these parts of the continent. Later, part of the original population died out, and species that crossed the ocean came to replace them.

How the settlement of oceanic islands took place was also tried to be clarified by Charles Darwin, who experimentally established that the fruits and seeds of many plant species remain viable when long stay in sea water, and during this time they can be delivered by currents to many islands. In addition, the seeds of some species can "travel" in the intestinal tract of birds without losing their germination. Finally, they can be delivered along with soil particles on bird feet and floating tree trunks. If we consider the issue more broadly, we can say that the methods of getting plants and animals to the islands are diverse: sea and air currents, storms and hurricanes, a fin, a man and his vehicles, active movement by water or air.

J. Gressit and S. Yoshimoto (1963) characterize the dispersal abilities of animals belonging to different systematic groups. They point out that among reptiles, for example, skinks and geckos are very widespread, while other groups of lizards, like snakes, as well as freshwater fish, are absent on many oceanic islands. Apparently, representatives of these two groups of lizards are well adapted to travel on floating tree trunks or on their clusters - "rafts". From other systematic groups, amphibians are very poorly tolerated by salt water. Therefore, the possibilities of their movement across the ocean are extremely limited.

Among the invertebrates living on oceanic islands, insects dominate, the second largest place is occupied by terrestrial molluscs. Insects are spread by all of these methods. Species distributed by humans differ markedly from others, since on the islands they are usually synanthropic, i.e. they use human food reserves, his clothes (kozheedy, moths, etc.) and dwellings, are associated with domestic animals and agricultural plants. Many of them have cosmopolitan areas. The transfer of insects by birds is rare. Salty water It has an extremely unfavorable effect on them, so the species that swim across the ocean are also few in number.

Mature plants rarely remain alive when transported across the ocean. So epiphytes can move with tree trunks. Usually, plants spread with the help of diaspores. Light seeds and spores are carried by the wind. Undoubtedly, an important role in the spread of the plant is played by a person who spreads weeds all over the world, including on the islands.

If two islands of different sizes have recently separated from the same continent, then on the larger island, the mainland biota is able to be preserved almost completely, and on the smaller one, the possibility of the existence of entire taxonomic groups, for example, representatives of the entire class of mammals, can be completely or almost completely excluded. . The limiting influence of the size of the island increases as its territory decreases.

F. Darlington (1957) for the Antilles established the following ratio between the size of the island and the number of species of amphibians and reptiles: with a decrease in the size of the island by 10 times, the number of species of these groups is halved.

How closer island located closer to the source of migration, the higher the degree of saturation with migrants. Biota of continental and oceanic islands obey this regularity. Although the resettlement of each individual is random, however, with long-term development migration processes they obey the law of large numbers, i.e. statistical probability. F. Darlington pointed out that if one individual out of 1000 successfully crossed a space 100 miles wide, then when overcoming the next 100 miles, one individual out of 1000 who passed the first 100 miles will successfully complete this task again. In other words, only one individual in a million will reach an island located 200 miles from the source of migration, and only one individual in a billion will reach an island located 300 miles from the continent.

The position of the island in relation to the direction of the winds also has a great influence. that cross it, the so-called "_________________" for insects and seeds of plants: if the island, elongated in length, is located perpendicular to the flow of migrants, then there will be more chances that any species will reach it; if the island is located along the main direction of movement, then the chances that organisms carried by wind or sea currents will fall on it will be much less.

The gradual extinction of species on the islands is evidenced by the fact that small islands of continental origin have an almost purely oceanic fauna, in contrast to large islands. So, among the Pearl Islands on big island The ray contains about a third of the continental species, and on small island Contadora - only 1 out of 10. As shown by the observations of J. Diamond on the islands off the coast Southern California, none of them had the number of species that could exist on it if this island were part of the mainland. Fifty years after the first observations on these islands, the number of species averaged almost half of what was possible.

Distribution, dispersion, - only ______________________ of the species on the island. It must go through a full cycle of development (ecesis) from appearing in a given place to bringing viable offspring. More tolerant and valence (i.e., with wide ecological capabilities) species pass through the stage of ecesis more easily than less tolerant and stenobiont ones.

Ecesis is carried out in the presence of favorable conditions for the life of the organism: light, heat, moisture, and especially write. It remains incomplete most often as a result of the unavailability of the necessary resources. Thus, many insects cannot settle on the islands due to the lack of food plants for their larvae or adults, or in cases where there are no open fresh water bodies necessary for passing through the first stages of development. Many birds are unable to breed due to the lack of suitable nesting sites on the island.

Among plants, the inhabitants of the coasts have the greatest opportunities for successful development and reproduction, the seeds of which, when they get to the island, meet there an environment close to the original one. On the contrary, the inhabitants of the highlands have little opportunity to transfer their seeds across the ocean (mountains are often located far from the coast) and very little chance for plants to undergo ecesis in their new homeland, where high mountains may not be.

The rate of settlement of the islands is low. True, specific data on the rate of this process differ greatly. Based on the number of species of flowering and vascular spore plants in the flora of the Hawaiian Islands and the geological age of this archipelago, F. Fosberg came to the conclusion that the successful development of the territory by plants was carried out here on average once every 20-30 thousand years, i.e. not more often than 30-35 settlements in 1 million years. However, this speed cannot be accepted for all islands. So, low-lying atolls are most often 4000-6000 years old. If we accept the population rate calculated by F. Fosberg for the Hawaiian Islands, the age of low-lying atolls is less than the period of their settlement by one species. In fact, in the flora of each of these atolls, there are up to several dozen species, of which not all have been introduced by humans. The uplifted atoll of Nauru, estimated by geologists to be about 100,000 years old, could be invaded by only 4-5 plant species at the rate calculated by F. Fosberg, while the atoll's flora includes almost 100 species. In addition, it should be borne in mind that the data on the flora are undoubtedly underestimated, since some plants that entered the island may subsequently die out. Thus, for many islands, the rate of their colonization is much higher than that calculated by F. Fosberg: for low-lying atolls it is one settlement in 200-300 years, for the elevated Nauru atoll - approximately one in 1000 years.

Most biogeographers believe that the penetration of species from the continent to certain islands could be facilitated by the existence of "stonework", i.e. intermediate islands and islets, which, over the course of geological history, either appeared from the waters of the ocean, or again hid in them. Most often, such temporary shelters were islands of volcanic origin.

island biota

The smaller the island, the more monotonous living conditions are, as a rule, on it. Both of these reasons explain the direct relationship that is observed between the size of the island and the number of species that make up its biota. This can be illustrated by the example of nesting birds.

The number of species living on the island also depends on other reasons, primarily on the age of the island and the degree of its isolation - remoteness from the mainland.

A necessary condition for speciation on islands is isolation. If everything is continuously carried out new and new

the introduction of individuals of the same species to the island, then as a result of crossing of individuals that previously lived here with individuals that have recently appeared, some stabilization of the characteristics of the species is observed, and the process of speciation slows down sharply. The process of speciation is also associated with the natural features of the islands. On high islands, where a significant variety of ecological conditions is observed in a small space, the possibilities for the emergence of new subspecies and species are higher than on low islands, with the uniformity of their natural features.

The absence of a number of life forms and systematic groups on the islands as part of their biota has led to the fact that some species, when they get to such islands, undergo the so-called adaptive radiation; the descendants of one species that has entered an island or archipelago change greatly. Thus, the ancestor of the flower birds Drepanididae, the American finch, having penetrated Hawaiian Islands, did not meet competitors here and gave rise to finch-like, honey-like, feather-like, woodpecker and oak-like forms. Several genera and many species of flower girls arose, which occupied various ecological niches, which made it impossible to repeat such adaptive radiation in later times. Similar examples of adaptive radiation are palm trees on the island of Cuba, some insects and molluscs in the Hawaiian Islands.

An example of the same adaptive radiation, but not as far advanced, is the psosutukava tree (Metrosideros kermadecensis) on Raul Island (Kermadec Archipelago). Depending on the conditions of the habitat, it forms forms that have not yet reached the level of species differences. So, it is a squat, pressed to the ground shrub in the lower parts of the slopes, exposed to the action of the ocean surf; low erect shrub on volcanic pumice at the bottom of the volcano caldera; a straight-stemmed tree in dense stands, a giant tree with outstretched horizontal branches in sparse stands, and finally an epiphyte and strangler tree when settling on tree trunks.

In other cases, as a result of speciation, monotypic genera and even families arise on islands. Such are the tree of degeneration from the fam. degeneriaceae Degeneriaceae on the island of Fiji, the kagu bird on New Caledonia.

A striking feature of island biotas is a large number of endemics, often of a high taxonomic rank. The number of endemics and the level of endemism depend on the size of the islands, their distance from the continent, the variety of ecological conditions, and the duration of isolation.

On the islands, deviations from the usual appearance of representatives of certain groups are often observed; gigantism or, conversely, ___________________. The reasons for this are unclear. Flightless birds and insects are often characteristic of the islands. For birds, the main role in the emergence of flightless species is played by the absence of mammals on the islands that could exterminate them. For insects, the drift of flying species into the ocean by wind and hurricanes. In order to survive, insects must either have a fast flight, or, conversely, lose the ability to fly, or hide in the wind in secluded corners. On many, even small islands, there are many species characterized by a fluttering, slow flight - lacewings, mosquitoes, bedbugs, small diurnal butterflies, moths. Their abundance is facilitated by the peculiarities of the lifestyle associated with the ability to hide from gusts of wind. Thus, natural selection should have contributed to the survival of non-flying individuals and eventually led to the formation of forms that have lost even the organs of flight.

Finally, the islands contribute to the preservation of primitive archaic forms. Examples are the New Zealand tuatara, an extremely primitive genus of insectivores - the flint tooth from the Antilles, the Madagascar ferret cat, or fossa. This is explained by the fact that in small isolated ecosystems, the existing structure of communities is protected by external geographical barriers from the intrusion of new, most active groups that have won the struggle for existence, which, successfully settling on the continents, invade previously formed ecosystems. It is noted that isolation on the islands contributes to the divergence of forms, i.e. geographical speciation, but at the same time, the evolutionary process here is slower than on the mainland.

A characteristic feature of island biotas in general, apart from endemism, is their poverty. This is explained by the extinction and the difficulty of migrants penetrating the islands. The number of species is subject to more or less significant fluctuations over the years. But over large areas, these ups and downs in numbers can occur only in some part of the species range. While in one place the number of a species is falling, in another it is rising. Thus, even if all individuals of a known species in one part of the range die out, then it will be relatively quickly populated from adjacent parts. On the islands, the species can easily disappear completely. It is clear that what less territory islands, the greater the chance for the species to go extinct.

The isolation of the biotas of individual islands is the reason for their slight disturbance when altered by humans. natural conditions. Deforestation and their replacement with plantations of both woody and herbaceous plants are often irreversible on the islands, especially the replacement of forests with fields. Therefore, giving examples of the extinction of species under human influence, we first of all recall the inhabitants of the islands: the Steller (sea) cow that lived off the coast of the Commander Islands, the wingless guillemot (Newfoundland Island), the moa (New Zealand), the dodo, etc.

However, the most catastrophic for the fauna and flora of many islands is the introduction by humans (conscious or unconscious) of new species to these islands. For example, goats on many islands have exterminated many plant species. The flora of St. Helena has lost, to goats, a considerable number of species of trees formerly characteristic of it; the same was noted on the islands of Kermadec and others. At present, detachments of hunters are sent to many islands, the purpose of which is to sharply reduce the number of these animals.

Herbivorous marsupial possum, introduced from Australia to New Zealand, destroyed forests in many parts of this country. Significant harm to the fauna of the islands is caused by rats that have got there. They destroy the eggs and chicks of birds nesting on the ground. So, on Raoul Island (Kermadec archipelago), they completely exterminated the Kermadec petrel, now preserved only on several small islands, where rats did not penetrate. To deal with rats that caused significant damage agriculture, in particular the cultivation of sugar cane and rice, the mongoose was introduced to Cuba and Fiji. However, not limited to eating rats, this animal has drastically reduced the number of birds nesting on the ground, in Cuba it almost destroyed the endemic species of the sand tooth, and in Fiji it minimized the number of the Fijian iguana.

Huge devastation in the composition of the animal population of the islands is produced by pigs. In New Zealand, they exterminated a representative of a monotypic endemic detachment - a tuatara, preserved only on small islands off the coast of New Zealand; almost exterminated flightless birds - kiwi and owl parrot, etc.

The introduction of European red deer to New Zealand led to the destruction of forests over a large area. It turned out that it is very difficult to exterminate this animal, introduced by man. The bonuses assigned for each animal killed did not help either. At present, New Zealand has moved to the creation of reindeer farms with a fierce struggle against the deer living freely on the island.

From the foregoing, it follows that any introduction to the island of species that did not previously exist here must be carefully considered. It is necessary to always remember the vulnerability of the nature of the islands and the difficulties, if not complete impossibility, of eliminating the consequences of such actions.

E evolution of island communities

The word "island" in this section does not necessarily mean a piece of land surrounded by water. Lakes are "islands" of water in the midst of land; mountain peaks - "islands" with high mountain conditions in the "ocean" of lower areas; the windows in the forest canopy, which arose when the trees fell, are "islands" in the sea of forest stand. We can talk about "islands" with a special geological structure, a certain type of soil or vegetation, surrounded by other rocks, soils or phytocenoses (Fig. 59). For all these types of "islands" one can also trace a regular relationship between species richness and area.

It has been established that the number of species on the island is the smaller, the smaller its area. Examples of such dependence for different groups organisms are shown in Fig.61. Usually, in its graphical representation, a logarithmic scale is taken for both parameters, although, if we correlate the number of species with the logarithm of the area, the resulting line is sometimes closer to a straight line. However, in simple coordinates, the dependence always looks like a curve, and with an increase in the area, the growth in the number of species slows down. Three approaches are used to study the processes of formation of island biotas: a) assess the diversity of habitats suitable for settlement on the island; b) pay attention to the ratio of the speed of two processes: the colonization of the island by species new to it and the extinction of those that have already settled (equilibrium theory); c) reveal the relationship between the settlement of the island from the outside and the evolution of species on it.

In reality, all these processes go on simultaneously, and the specific result - the uniqueness of the island biota - is the result, the balance of their interaction.

One of the major achievements of biogeography of our time is the creation by MacArthur and Wilson (1967) of the “equilibrium theory of island biogeography”, based on a mathematical apparatus for describing the dynamic process of species migration to islands and their extinction, as well as the nature of the established species equilibrium. Its essence - the number of species inhabiting the island, is determined by the balance between immigration and extinction. How this happens is shown in Fig. 62. Consider first immigration. Imagine an uninhabited island. The intensity of species immigration for it will be high, because any individual that has settled here represents settled species; the rate of introduction of new (not yet represented) species is reduced. It will vanish when all species of the "original population" (i.e., the neighboring mainland or nearby islands) have settled on the island.

The specific immigration curve depends on how far the island is from the source of its potential settlers. Zero will always be marked at the same point (all types of the “initial population” are represented on the island), but the function as a whole will have the higher values, the closer the source of immigration, i.e. the more likely migrants are to reach the island. The rate of introduction to large islands, as a rule, is higher than to small ones, since the former are more accessible.

The extinction rate is zero when there are no species on the island, and generally low when there are few. However, as the number of settled species grows, it, according to the theory, increases.

To consider the combined effect of immigration and extinction, let's superimpose both graphs on top of each other. The number of species corresponding to the point of intersection of the curves (S*) reflects the state of dynamic equilibrium, i.e. potential species richness of the island. Below this point, species richness increases (the rate of immigration exceeds the rate of extinction), and above this point it decreases (extinction is more intense than immigration). This theory allows us to make a number of assumptions about the formation of island communities.

1. The number of species on the island should eventually roughly stabilize.

2. This stabilization is not the result of the constancy of the species composition, but of the continuous change of species, when some forms die out, while others are introduced.

3. There are more species on large islands than on small ones.

4. Species richness will decrease as the island moves away from the sources of settlement.

Main question island biogeography - is there an "island effect" as such, or are islands poorer in species simply because of their small territory and small number of habitats? A number of studies have attempted to separate the species-to-area ratio for islands from components that are fully explained by habitat heterogeneity from those that are due to area. For example, the diversity of fish species in the lakes of northern Wisconsin is significantly correlated with both the area of the lake and the diversity of its vegetation. A clear relationship has also been found between the species richness of birds and the area of islands off the coast of Western Australia (Abbott, 1978).

Investigation of the relationship between the number of species, the area of the island and the diversity of bird habitats on the islands Aegean Sea(Watson 1964) showed that habitat diversity is a more important factor than area.

The equilibrium theory is also applicable to phytophagous insects (Janzen, 1968): relatively widespread plants can be considered as relatively "large islands" surrounded by a "sea" of different flora. In addition, a certain type of plant can be considered "remote" from others if it is specific in its morphological, biochemical or other biological features. Thus, it follows from the equilibrium theory that insect species richness will be higher on plants with large ranges and lower on geographically isolated or rare species, as well as on morphologically or biochemically "isolated" plants.

The equilibrium theory is in good agreement with the data on the islands, which in the past were part of the isthmus connected to the mainland, which then submerged under water. If the equilibrium number of species is to some extent determined by the ratio between the rate of extinction and the area of the island, it must be assumed that such recently detached landmasses will lose species until a new equilibrium is established corresponding to their size. This process is called "relaxation". Thus, the relationship between the time of separation of the islands of the Gulf of California from the mainland and the number of lizard species found on them has been described (Wilcox, 1978).

The equilibrium theory assumes for an “island” not only the presence of a characteristic species richness, but also a constant “circulation” of species, i.e. the continuous settlement of new forms and the extinction of those already present. This means that the specific composition of the island biota at each moment of time must be largely random.

It has long been noted that one of the main features of island biotas is the "disharmony" of the taxonomic and trophic structure of the community (Hooker, 1866). This implies a different than on the mainland, the relative participation of various taxa in the composition of the biota, in the construction of food webs of island ecosystems. Considering the relationship between the number of species and area, we have already seen that organisms that are able to disperse well (such as ferns and birds) are more likely to inhabit individual islands than species in which this ability is not so developed (most mammals, practically all conifers). The potential possibilities of dispersal of individual species, of course, are not the same within such groups. On fig. 63 shows the eastern borders of distribution across the islands Pacific Ocean various terrestrial and freshwater birds found in New Guinea, the fauna of which is halved over a distance of 2600 km from the settlement area. At the same time, it turned out that most species of land snails of the Pacific region, being very small in size, are easily transferred from island to island, and most of the beetles of Saint Helena are xylophages or subcrustal forms, brought here, most likely, through the sea along with floating tree trunks.

However, different dispersal abilities are not the only reason for disharmony. Species with a low density per unit area under natural conditions will always be represented on the islands by extremely small populations, for which the probability of complete extinction as a result of random fluctuations is very high. On many islands, the absence of predators is striking, the populations of which, as a rule, are relatively small. For example, in the Tristan da Cunha archipelago in the South Atlantic, there is not a single bird-eating predator, not counting those brought here by man.

Predators may also be absent from the islands because their immigration can only lead to settlement on the island if their prey has already settled there (whereas such dependence on predators does not exist for prey species). This is also true of parasites, mutualists, and the like. In other words, disharmony in the settlement of the islands arises from the fact that some categories of organisms are more “dependent” than others.

ISLAND BIOTA

Table 7

Number of nesting bird species on islands of various sizes

Island	Area, km 2	Number of species	Island	Area, km 2	Number of species
New Guinea	758 000	495	haining	34000	169
Sumatra	434 000	430	Flores	15000	141
Java	125000	337	Azores	2388	34
Sri Lanka	65000	251	bermuda	965	13

The number of species living on the island also depends on other reasons, primarily on the age of the island and the degree of its isolation - remoteness from the mainland.

A necessary condition for speciation on islands is isolation. If more and more individuals of the same species are continuously introduced to the island, then as a result of crossing of individuals that previously lived here with individuals that have recently appeared, some stabilization of the characteristics of the species is observed, and the process of speciation slows down sharply. The process of speciation is also associated with the natural features of the islands. On high islands, where a significant variety of ecological conditions is observed in a small space, the possibilities for the emergence of new subspecies and species are higher than on low islands, with the uniformity of their natural features.

The absence of a number of life forms and systematic groups on the islands as part of their biota has led to the fact that some species, when they get to such islands, undergo the so-called adaptive radiation: the descendants of one species that got to the island or archipelago change greatly. Thus, the ancestor of the Drepanididae flower birds, the American finch, having penetrated the Hawaiian Islands, did not meet competitors here and gave rise to chaffinformes, honeybees, pikas, woodpeckers, and grosbeaks. Several genera and many species of flower girls arose, which occupied various ecological niches, which made it impossible to repeat such adaptive radiation in later times. Similar examples of adaptive radiation are palm trees on the island of Cuba, some insects and molluscs in the Hawaiian Islands.

An example of the same adaptive radiation, but not as far gone, is the pohutukawa tree. (Metrosideros kermadecensis) on the island of Raul (Kermadec archipelago). Depending on the conditions of the habitat, it forms forms that have not yet reached the level

species differences. So, it is a squat, pressed to the ground shrub in the lower parts of the slopes, exposed to the action of the ocean surf; low erect shrub on volcanic pumice at the bottom of the volcano caldera; a straight-stemmed tree in dense stands, a giant tree with outstretched horizontal branches in sparse stands, and finally an epiphyte and strangler tree when settling on tree trunks.

In other cases, as a result of speciation, monotypic genera and even families arise on islands. Such are the degeneria tree from the degeneriaceae family Degeneriaceae on the island of Fiji, the kagu bird on the islands of New Caledonia.

On the islands, deviations from the usual appearance of representatives of certain groups are often observed: gigantism or, conversely, dwarf sizes. The reasons for this are unclear. Flightless birds and insects are often characteristic of the islands. For birds, the main role in the emergence of flightless species is played by the absence of mammals on the islands that could exterminate them; for insects, the drift of flying species into the ocean by wind and hurricanes. In order to survive, insects must either have a fast flight, or, conversely, lose the ability to fly, or hide in the wind in secluded corners. On many, even small islands, there are many species characterized by a fluttering, slow flight - lacewings, mosquitoes, bedbugs, small diurnal butterflies, moths. Their abundance is facilitated by the peculiarities of the lifestyle associated with the ability to hide from gusts of wind. Consequently, natural selection must have contributed to the survival of non-flying individuals and eventually led to the formation of forms that have lost even the organs of flight.

Finally, the islands contribute to the preservation of primitive (archaic) forms. Examples are the New Zealand tuatara, an extremely primitive genus of insectivores - the flint tooth from the Antilles, the Madagascar ferret cat, or fossa. This is explained by the fact that in small isolated ecosystems, the existing structure of communities is protected by external geographical barriers from the intrusion of new, more active groups that have won the struggle for existence, which, successfully settling on the continents, invade previously formed ecosystems. It is noted that isolation on the islands contributes to the divergence of forms, i.e. geographical speciation, but

at the same time, the evolutionary process here proceeds more slowly than on the mainland.

The island biota in general, except for endemism, is characterized by poverty. This is explained by the extinction and the difficulty of migrants penetrating the islands. The number of species is subject to more or less significant fluctuations over the years. But over large areas, these rises and falls in numbers can occur only in some part of the range of the species, while in one place the number of the species falls, in another it rises. Thus, even if all individuals of a known species in one part of the range die out, then it will be relatively quickly populated from adjacent parts. On the islands, the species can easily disappear completely. It is clear that the smaller the territory of the island, the less chance for the species to survive.

The isolation of the biotas of individual islands is the reason for their slight disturbance when natural conditions are changed by humans. Deforestation and their replacement with plantations of both woody and herbaceous plants are often irreversible on the islands, especially the replacement of forests with fields. Therefore, when citing examples of the extinction of species under human influence, one should first of all mention the inhabitants of the islands: the Steller (sea) cow that lived off the coast of the Commander Islands, the wingless guillemot (Newfoundland), moa (New Zealand), etc.

However, the most catastrophic for the fauna and flora of many islands is the introduction by humans (conscious or unconscious) of new species to these islands. For example, goats on many islands have exterminated many plant species. Flora o. St. Helena has lost, to goats, a considerable number of species of trees formerly characteristic of it; the same was noted on the islands of Kermadec and others. At present, detachments of hunters are sent to many islands, the purpose of which is to sharply reduce the number of these animals.

Herbivorous marsupial opossum, brought from Australia to New Zealand, destroyed forests in many parts of this country. Significant harm to the fauna of the islands is caused by rats that have got there. They destroy the eggs and chicks of birds nesting on the ground. So, on about. Raul (Kermadec archipelago) they completely exterminated the Kermadec petrel, now preserved only on a few small islands, where rats did not penetrate. To combat rats, which caused significant damage to agriculture, in particular the cultivation of sugar cane and rice, the mongoose was introduced to Cuba and Fiji. However, not limited to eating rats, this animal has drastically reduced the number of birds nesting on the ground, in Cuba it almost destroyed the endemic species of the sand tooth, and in Fiji it minimized the number of the Fijian iguana.

Huge devastation in the composition of the animal population of the islands is produced by pigs. In New Zealand they exterminated the representative

monotypic endemic detachment - tuatara, preserved only on small islands off the coast of New Zealand; almost exterminated flightless birds - kiwi and owl parrot, etc.

Organisms enter the islands in various ways. C. Darwin during the expedition on the "Beagle" took air samples in the open ocean, in which he found spores, seeds, insects, cobwebs carried by the wind. It is known that seeds, plant spores, mites, insect eggs and even fish eggs can be carried on the paws and feathers of a bird. Sailors often saw natural rafts of intertwined plants, which were so huge that they were mistaken for islands and put on the map. These natural rafts could carry small mammals, reptiles, insects, spiders, centipedes, snails, and other creatures (Fig. 29).

Once on the islands, terrestrial plants and animals, often unable to float or swim, found themselves closed in their island world. In what direction does natural selection act on island species? There are four main trends here: gigantism, dwarfism, winglessness, intraspecific diversity.

Many island animals, especially birds and reptiles, reach large sizes (Fig. 30). The largest birds that ever existed on Earth lived on the islands: moas in New Zealand and epiornis (elephant birds) in Madagascar. Moa reached a height of three meters, i.e. were almost twice as tall as a person and weighed about 250 kg, and eggs - 7 kg! Epiornis were not as tall as the moa giants, but almost twice as heavy and laid eggs up to 35 cm in diameter, one such egg is equal in volume to 180 chicken eggs. The gigantism of these flightless birds, as it was possible to find out from the study of brain castings, was due to mutations that led to the overdevelopment of the pituitary gland. Gigantism extended not only to animals. Giant buckwheat grows on Sakhalin; many other Sakhalin plants are gigantic. Some shrubs and herbs are not inferior to trees, such as plantain on canary islands, Ivy In New Zealand. On the island of Socotra Indian Ocean endemic trees grow with monstrously developed trunks in which water is stored, they are related to melons and cucumbers.

In the development of some animals, mainly mammals, the opposite trend was reflected. An example of this is the pony (pygmy horse) in the Shetland Islands. By reducing their size, mammals, as it were, expanded their range.

Other characteristic island animals - loss of the ability to fly. The giant birds in question did not have wings, the Mascarene giant doves, Galapagos cormorants, New Zealand kiwis are not capable of flying. In New Zealand, there is a wingless parrot that nests in burrows. Apparently, in the absence of predators and with an abundance of food, flying qualities were not necessary for large birds, and gradually, due to the accumulation of mutations and natural selection, they lost them.

Wingless insects are also common on oceanic islands, since winged ones were more often picked up by the wind and died in the ocean.

Adaptive diversity can also be observed in animals living on archipelagos. Suffice it to recall the Galapagos finches and Hawaiian flower girls, each species of which is confined to a particular island or specialized in a way of feeding, which eliminates competition and the species exist side by side.

Finally, the inhabitants of the islands, as a rule, are very trusting. This is explained by the fact that in the absence of natural predators, animals lose their hereditary behavioral skills associated with protective fear.

For a long time, geographical isolation contributed to the preservation of the endemic flora and fauna of the islands. But the security of life on the islands ended the day the first ship appeared on the horizon. Island animals were unarmed before the advent of man. Flightless birds suffered the greatest losses: moas, epiornis, dodos, etc. disappeared. It is easy to understand that species that are not able to fly are the easiest prey for humans and their companions - dogs and cats. A fatal role was played by the introduction of new species on the islands, accidentally or deliberately introduced by man. Even in the XVII-XVIII centuries. crews of ships left goats and pigs on the islands to provide food for the future. These abandoned animals exterminated the native flora so intensively that many plant species almost completely disappeared, and animals disappeared with them: insects, birds, reptiles, some mammals, which plants served as food and shelter.