In animal species that find themselves isolated on islands. Amazing animals that live on the islands. The largest animals

Since the time of Darwin, the rule of islands has been known: if animals are placed on an isolated island, they will change sizes over time - large ones will become small and vice versa. And recently it turned out that if a sea creature is “sent” for permanent residence deeper, the same effect will occur.

Biologists are well aware of the possibility of such a slightly strange course of evolution. For example, mammoths in the Channel Islands, isolated from the rest of the world, developed into an entirely new species that became so “miniature” that their weight was only one-tenth that of their relatives on the mainland.

There is also the opposite case - shrews on some Caribbean islands. Over time, these tiny rodents developed into thirty-centimeter "monsters".

All these examples confirm: yes, on islands large creatures decrease, and small ones grow.

In recent decades, this trend has been called the island rule in biology. The only trouble is that scientists consider the question of the applicability of this rule as controversial, as well as its foundations.

This picture schematically shows how animals on the island change after isolation: large ones (for example, elephants) become smaller, and small ones (for example, shrews) become larger (illustration by MBARI).

For example, the reason for the decrease may be the struggle for existence that animals begin to wage in conditions of lack of food and territory. On the other hand, increasing the size may be an advantage, especially if smaller predators live on the island.

It is clear that such factors influence evolution, but how exactly, and what their combination should be, is a separate difficult question.

But it seems that this is not only a matter of interspecies struggle. Thus, Craig R. McClain, an employee of the Monterey Bay Aquarium Research Institute (MBRI), suggested that a similar trend may exist in other places isolated from the outside world, in particular, deep underwater.

This illustration demonstrates how the "island rule" subjugates deep-sea and shallow-sea snails. At depth, large ones evolve into small ones, and vice versa. Almost the same as with elephants and mice (illustration by MBARI).

At the 11th International Deep-Sea Biology Symposium taking place these days, he presented the results of his research (PDF document, 156 kilobytes), in which he applied the island rule to underwater snails.

As a marine biologist, McClain became interested in the question of why deep-sea inhabitants evolve into species that differ significantly in size from their shallow-sea relatives. But the scientific literature did not shed any light on the mystery, and the proposed theories contradicted each other. I had to figure it out on my own.

So Craig came to the hypothesis that the mechanism could be the same as in the case of islands, because marine inhabitants periodically “capture” the depths (as do animals that “colonize” islands).

On the right side of this photo are three shells of medium-sized shallow water snails. The three faint dots at the top end of the line are the shells of relatives of deep-sea snails (photo by Craig McClain).

To test the correctness of their idea, McClain and his colleagues decided to compare the sizes of aquatic snails living at the surface and at the bottom.

They approached the matter, it must be said right away, with extreme conscientiousness. To obtain statistically reliable data, they analyzed data on thousands of Atlantic Ocean snails using a specially created database. And the different statistical methods that the researchers used led to the same results.

It turned out that if shallow-water snails were less than 12 millimeters in size, then they generally had larger deep-sea relatives; if they were more than 20, then their underwater relatives were small. As McClain speculates, "these snails have evolved to be a size compromise for different pressures."

Dr. Craig McClain: “One of the problems with our research is that we can't do experiments. Therefore, all we can do is collect as much data as possible” (photo from mbari.org).

In general, the hypothesis was confirmed - snails adapt deep underwater according to the same principle as animals on the islands. But McClain's theory says nothing about the characteristics of individual species that fall into such isolation. In addition, obviously, not everything that is applicable to aquatic inhabitants is suitable for land animals.

Madagascar is home to some unique and unusual species of fauna. The island is home to almost 25,000 species of wildlife, many of which are endangered. Over the past 2,000 years, Madagascar's biologically rich forests have been reduced by almost 90%, largely due to agriculture and other commercial activities such as logging.

The massive outbreak has brought several island animals to the brink of extinction. Lemurs, which exclusively inhabit Madagascar, are the most endangered and are listed on the Red List of Threatened Species. The bamboo lemur, named after its favorite food, is critically endangered because its habitat has been reduced to 4% of its original size.

Madagascar is located in the Indian Ocean on the southeast coast of Africa, and is the 4th largest island in the world. This is a place dominated by endemic species of animals and plants that are found nowhere else in the world. The island was isolated for several million years, allowing animals and plants to evolve and diversify in a small area.

About 170 million years ago, Madagascar was a landlocked territory within the continent of Gondwana. As a result of the movement of the earth's crust, Madagascar and India separated from South America and Africa, and then from Antarctica and Australia. Around 88 million years ago, India also separated from Madagascar, allowing animals on the island to evolve in relative isolation.

Lemurs

Lemurs are primates that look like an animal similar to a dog, cat and squirrel. They exhibit incredibly unique and exciting behavior, including singing sounds reminiscent of whales. Today there are more than thirty species of lemurs in Madagascar, ranging in size from the 25 g dwarf mouse lemur to the largest indri lemur weighing over 12 kg. Lemurs are one of the most endangered animals on the entire planet, and according to the IUCN Red List, they are considered critically endangered, with 22 species critically endangered; 48 species are endangered and 20 are vulnerable.

Fossa

The Fossa lives in the forests of Madagascar and is a close relative of the mongoose. It grows up to 1.8 m in length from tail to nose and weighs up to 12 kg. The animal has a slender body and looks more like a mongoose than a mongoose. The Fossa uses its long tail to move quickly through the trees. The animal is classified as a critically endangered species and is listed on the IUCN Red List due to its habitat loss. Today, less than 10% of Madagascar's original forest cover remains, which is also the only home of the fossa.

Madagascar comet

Madagascar comet ( Argema Mittrei) is one of the most beautiful butterflies in the world, found only in Madagascar. The wingspan can reach 20 cm. The insect has a bright yellow color and long “tails” on the lower wings. Females are wider, their wings are round, and their tail is shorter than that of males. Until now, these beautiful animals do not have protected status, and their population size has not been established.

Panther chameleon

The panther chameleon is endemic to Madagascar and other nearby islands. It has the most variety of colors of any chameleon and is most sought after by reptile traders. Like other chameleons, the panther chameleon has a raised nape. When hunting, it uses its tongue with a suction cup at the end. This species is least endangered.

Fantastic leaf-tailed gecko

Fantastic leaf-tailed gecko ( Uroplatus Phantasticus) is a stunning reptile that can camouflage itself in its environment. Its body is similar to dead leaves, which helps the animal hide from predators. The gecko is covered in patterned skin and its tail looks like it has been chewed by insects. All these features help it blend in well with the surrounding foliage. Fantastic leaf-tailed geckos vary widely in color, but they are generally brownish with some spots on the belly, which sets them apart from other similar species.

They are nocturnal reptiles with large eyes that are suitable for hunting insects in the dark. They also have sticky scales under their toes and strong claws that allow them to move quickly through trees. Geckos live in a specific habitat and are not tolerant of any changes. Due to their appearance, leaf-tailed geckos are beloved pets and are one of the best-selling species. Recently, there has been a decline in population numbers in the wild.

Tomato frog

Also known as tomato narrowmouth frogs, these frogs are found only in Madagascar, mainly in the northwestern part of the island. As a rule, they lead a terrestrial lifestyle and are common in forested areas. Due to deforestation, their habitat has been destroyed, but they appear to adapt well to changed conditions and can be found in gardens and plantations.

There are three types of tomato frogs: Dazzophus antongilli, Dyscophus guineti And Dyscophus insularis. Of the three, D.antogilli is endangered due to deforestation and trapping for keeping as pets. These frogs mate during the rainy season, in shallow, slow-moving water. They are brightly colored and can secrete a nasty substance when threatened, although it is not toxic but can irritate the mucous membrane.

Red foodie

Also called the Madagascar fody, this bird is native to Madagascar and other nearby islands such as the Comoros, Seychelles and Mauritius, and the species has recently been found as far away as the Arabian Peninsula. They grow to about 12.5-13.5 cm and weigh about 14-19 g. Males have bright plumage on the chest and head, while the wings, tail and eye area have dark feathers. The plumage varies widely from orange to yellowish, and during breeding the males molt and become olive-brown like the females. The species is least endangered.

Madagascar hissing cockroach

The Madagascar hissing cockroach is one of the most fascinating endemic animal species on the island. It has an oval shape and a shiny brown body without wings, but with a pair of raised horns in the males. During conflicts, these insects hiss, which is how they got their name. Unlike most insects, which create noise through body parts or vibration, the Madagascar cockroach hisses by contracting its abdomen and forcing air through its spiracles. The insects can live from two to five years and grow up to 5-7 cm in length.

Madagascar bat

The Madagascar bat is a nocturnal primate that lives primarily in trees. Their thumbs and long tails allow them to stay comfortable in trees while they use their echolocation to find food such as insects. They also have sensitive large ears and eyes that help them find food. Because of their bizarre appearance, they were considered a bad omen among the locals of Madagascar. The species is on the verge of extinction.

Madagascar long-eared owl

This bird has a body length of about 50 cm, making it the largest owl on the island. Females are usually larger than males. The owl is characterized by a brownish crown on the top of its head. She also has a brown facial disc. The Madagascar owl is primarily nocturnal. The species is least endangered.

Striped tenrec

The striped tenrec is common in the lowland northern and eastern parts of Madagascar. The animal has a long pointed snout, vestigial tail and limbs. The muzzle is black with yellow stripes, and the body is covered with spines. The striped tenrec is active both during the day and at night and feeds mainly on insects. The long muzzle is designed mainly for digging in the ground in search of prey. They can also feed on worms, small fish and even frogs. Tenrecs mainly breed in October and December depending on the availability of food. The gestation period is 58 days and the female can give birth to up to eight cubs. The species is of least concern.

Black mantella

Known as Mantella madagascariensis, the black mantella is a brightly colored frog with green, black, yellow or orange colors. The species is found only in eastern and central Madagascar. These frogs live in tropical forests bordering freshwater bodies. They can tolerate moderate temperatures between 24ºC and 27ºC during the day and slightly lower at night. The black mantella is a carnivorous animal that primarily feeds on insects. Frogs are active during the day, usually occupying small territories. The bright body color acts as a warning of danger to any predator. The species is in a vulnerable position.

Somewhere around 50-100 thousand years ago, there was the Indonesian island of Flores, where humanoid species lived. Like modern humans, members of these communities, called Homo floresiensis, built houses, foraged for food, prayed, and even used fire. The differences were in the small volume of the brain, huge teeth, prominent foreheads and very large feet. But their height was approximately 1.1 meters.

Why were these inhabitants, also known as "hobbits", so short? Some scientists believe this may be the result of the controversial theory of so-called insular dwarfism being put into practice. Its supporters are of the opinion that creatures living on land areas surrounded by water dry out and decrease in size.

Features of the sizes of representatives of island species

Hominins are not the only animals whose size has been attributed to insular dwarfism. Isolated on tropical Flores, Homo flores most likely hunted the same small animals like dwarf elephants. In Mediterranean Cyprus, for example, about 10 thousand years BC, small hippos lived about 0.7 meters high and about a meter in length. And in Crete at that time, for example, there lived dwarf mammoths no more than a meter high.

Observation results

“Observations have shown that large animals decrease in size when living in isolated environments, while small animals, on the contrary, increase in size,” says Aida Gomez-Robles, an anthropologist at the University of St. George Washington. - Island ecosystems tend to have fewer predators than mainland ecosystems. In this regard, animals have a need to reduce their consumption of plant foods, reducing their size in order to survive. And small individuals have a need to improve their metabolism, promoting their own growth in order to use accumulated fat as an energy source.”

Is it possible to trace a pattern?

Many famous examples illustrating the island rule can be found on the same island where Homo Flores once flourished: along with dwarf hominins and elephants, Flores was home to giant rats measuring about 0.4 meters in length, as well as the Komodo dragon - a type of lizard that can reach 3 meters in length and weigh more than 130 kg.

Differences of opinion

But despite such examples, the theory is hotly contested. At the 2007 Proceedings of the Royal Society, for example, some argued that this was not evidence for the existence of the island rule and that the patterns observed by past scientists were not sufficient to make a rule out of them. The authors agreed that the size of species living on islands may vary due to other features of the ecosystem of each particular landmass.

Is the "island rule" a valid argument?

The researchers once again traced the formation of this rule, starting with the records of Bristol Foster in 1964, who first began to determine the difference in the sizes of representatives of various species living on the islands in close interaction. Foster argued that rodents always reach record lengths in this habitat, and large animals always decrease in size. After this publication, other scientists began to use the results of his observations on all other mammals. Then in 1973, Lee van Valen first coined the term "island rule" in the article "Species and the Equilibrium of Nature."

"You can't base your theories on a single publication that lacks hard evidence," says Matt Tockery, a researcher at the Smithsonian Institution. The same evolutionary process set in motion by the island rule can be set in motion on the mainland if a particular ecosystem is isolated.

The theory with Homo floresiensis also has several versions of explanations. Some support the idea that while Homo erectus evolved on the mainland and increased in size, these creatures shrunk, relying on less food to survive. And others believe that people descended from larger monkeys, and the inhabitants of Florence from dwarf monkeys, as a result of which they inherited their small size. In addition, our ancestors also had shorter stature than modern inhabitants of the Earth. Perhaps the whole point is that such sizes were typical for all inhabitants of the planet at that time.

Lack of data prevents theory building

Tokeri said he disagreed with the island theory. Indeed, in order to find more compelling evidence, you need to carefully examine the fossils and remains of animals of those times, find out what their original size was. In the meantime, there are no such reports, drawing conclusions and building a theory on them or deducing a rule is extremely unscientific. It is necessary to trace how specific species got to the island, whether they evolved elsewhere, then ended up in isolation, or developed in the conditions prevailing in a given ecosystem, what their food chains were, etc.

And we certainly cannot assume that people currently living on the islands are “drying out” as a result of their isolated life. After all, with the development of various technologies, their isolation is rather conditional, and we eat not only what we get from hunting, but also start livestock farms, bring food from the mainland, and fish. Thus, this theory still does not have any solid basis and it cannot be said that this is a really working rule.

Everyone knows that the flora and fauna of the islands is often very, very different from that on the continent. And the example of the hobbits, who degraded on the wonderful island of Flores to an almost bestial state, is quite indicative. (Recall that Flores man, the so-called hobbit, came to the Indonesian island of Flores approximately 95 thousand years ago and lived there until 12 thousand years ago, degrading in the conditions of a warm and fertile island to the level of australopithecus with a brain volume of only 400 sq. cm).

“Ever since the time of Darwin, who studied the Galapagos finches, remote islands have been considered unique “evolutionary laboratories” in which species undergo rapid and sometimes very sophisticated evolutionary changes,” writes Alexander Markov in his book “The Birth of Complexity. Evolutionary biology today: unexpected discoveries and new questions."

Thus, large animals, finding themselves on such an isolated island with depleted vegetation, often become smaller, while small ones, on the contrary, become giants. And in a very short period of time. At least, this is the case with many species.

In 2006, Virginia Millien of McGill University (Canada) conducted a study comparing data on 86 island and 84 mainland mammal populations. For each of them, the rate of evolutionary changes in one or more dimensional traits was calculated over a certain time period.

Millien came to the conclusion that morphological evolution on the islands is indeed faster. However, this is noticeable only at intervals of less than 45 thousand years. As the time period increases, the differences between mainland and island populations become statistically insignificant.

Such differences cannot be explained by the fact that some animals are more common on the islands than on the mainland, and vice versa. “It turned out that the pace of evolution is not “phylogenetically conservative,” writes Markov. “For example, species that have evolved more slowly than others on a continent will not necessarily continue to behave in a similar way on an isolated island.”

According to the author, mammals that find themselves in the conditions of an isolated island very quickly adapt to them, and this sometimes leads to serious changes in the size and proportions of the animals’ bodies. Due to the high “speed” of these transformations, scientists are unable to detect transitional forms between island endemics and their mainland ancestors. However, after the changes occur, the rate of evolution of island animals usually slows down - in connection with this, it was not possible to identify differences between the rates of evolution over an interval of over 45 thousand years.

The so-called fragmentation of natural habitats (due to human fault as well) can lead to animals finding themselves in conditions similar to those of an isolated island. In this case, we should also expect rapid changes according to the “island” scenario. This situation has occurred, for example, with 25 species of mammals in Denmark whose bodies have evolved dramatically over the past 200 years.

“The rate of evolution can increase threefold or more in just a couple of decades. It turns out that under conditions of growing anthropogenic pressure on natural ecosystems, many animals familiar to us may begin to change in the most unexpected and rapid way,” Markov sums up.

Research question. In animal species that found themselves isolated on islands, during evolution
changes in body size often occur, both in the direction of increase
(giant Maltese swan), and downward (dwarf
Maltese elephant). What factors predict whether an organism will grow?
during such evolution or will it decrease? What other terrestrial and aquatic biotopes
show a similar evolutionary effect? Why is this effect more common?
only applies to animals and not to other living organisms?

Objectives of the study.

Conduct an analysis of the necessary literature;
Analyze factors that help predict size change
body;
Explore different biotopes and find those that exhibit similar
evolutionary effect;
Analyze the reasons why this evolutionary effect is more often

Giant swan and pygmy elephant

GIANT SWAN AND
Dwarf Elephant
C
What factors contribute to changes in the size of an organism?

Island gigantism and island dwarfism.

Gigantism (on the islands)
appears when
no restrictions,
that is, with abundance
food, lack
natural enemies,
competitors.
Dwarfism (at
islands) manifests itself
in the presence of
restrictions, that is
when there is a lack of food,
in the presence of natural
enemies, competitors.
Also for sizes
may be influenced by climate and
type of terrain.

Biotopes in which changes in the size of organisms are observed.

BIOTOPE IN WHICH
CHANGES ARE OBSERVED
SIZES OF ORGANISMS.
C
Seas and oceans ∙ Forests ∙ Steppes ∙ Savannahs ∙ Deserts and ice deserts

Seas and oceans.

Under pressure
Weight change underwater

Forests.

"Giants"

Forests.

"Dwarves"

10. Steppes.

"Dwarves"
"Giants"

11. Savannahs.

"Giants"

12. Savannahs.

"Dwarves"

13. Deserts and ice deserts.

Deserts
Ice deserts

14. Why does this effect more often apply to animals?

WHY IS THIS EFFECT MORE COMMON?
SPREADS ON
ANIMALS?
C

15.

Quite important in
occurrence of mutations
the following factors:
1.
Change of generations
2.
Availability
restrictions
3.
Mobility
For example, the same
plants are immobile,
small shift
generations. They are growing
these organisms in
throughout life.
Animals are the opposite
– mobile, frequent
generational change, growth
limited, from what
final size
the body and depends.

16. Research results.

An analysis of the necessary literature was carried out;
Factors that help predict size change are analyzed
body;
Various biotopes were explored and those that demonstrate similar
evolutionary effect;
The reasons why this evolutionary effect is more often
affects animals and not other living organisms.

17. Conclusion.

At first sight
evolution seems
unpredictable,
amazing
phenomenon, but
having analyzed
various
factors, conditions, in
which live
organisms, you can
line up
some forecasts
and guess how
this will change
organism.

18. List of references.

Raia, P.; Meiri, S. (2006). “The island rule in large mammals: paleontology meets
ecology"
Shilov I. A. “Ecology”
Biotope // “Biological Encyclopedic Dictionary” chapters. ed. M. S. Gilyarov.