Basics of Evolution - Korzh O.P. - 2006

Part II. MACROEVOLUTION

Chapter 15. Megaevolution

15.5. Evolution of Insular Ecosystems

The uniqueness of island flora and fauna has always attracted great attention from specialists (Ch. Darwin's stay on the Galapagos Islands resulted in The Development of evolutionary theory; A. Wallace's book "Island Life", etc.). Such interest is explained by the relative simplicity of biocenoses and trophic structures in island ecosystems, as well as the presence of unusual life forms. Today, The Study of the dynamics of insular communities is singled out as a separate scientific field—island biogeography, or island ecology—which holds both theoretical and practical significance (especially in nature conservation).

Islands feature a somewhat impoverished set of taxa and "unfilled" ecological niches within communities (a certain deficiency). Their territorial isolation consistently promotes the development of endemism (local Organism forms are shaped).

At the same time, the degree to which these features manifest is never identical across different insular territories (sometimes

certain areas with drastically different conditions and a high degree of isolation can be equivalent to island ecosystems, such as desert oases).

Several types of islands are distinguished, characterized by different landscape-environmental conditions and species composition. Based on The complexity of the landscape and territorial ecological Structure, the following types of islands are identified:

1) biogenic (coral);

2) volcanic;

3) geosynclinal (major elements of island arcs);

4) continental (lying on the continental shelf).

A classical Classification of islands is based on their origin, which divides them into oceanic, continental islands, and peripheral archipelagos.

An island of continental origin (Examples include the British Isles, Sunda Islands, Taiwan, New Guinea, etc.), upon separating from the mainland, inherits a specific (always incomplete) set of habitats and associated species. This is followed by a reduction in initial diversity, and the remaining species begin to form local variants.

Islands of oceanic origin (Saint Helena, Polynesian archipelagos, etc.) initially lack living organisms altogether, and their colonization occurs exclusively through passive and active immigration. A continuous enrichment of the species composition of these new formations takes place until a steady state is reached.

Peripheral archipelagos represent chains of islands along continental shores or between two continents (such as the Kuril Island ridge). These islands inherit part of their flora and fauna from the respective mainlands, another part results from dispersal, and the rest emerges through local Evolutionary Processes.

Regardless of their origin, the flora and fauna of islands always appear impoverished compared to mainlands, characterized by the absence of certain typical forms, pronounced endemism, and other specific traits. A certain dwarfing (reduction in size) of individual species also occurs compared to their mainland forms (believed to be due to the limited resources of island ecosystems).

Island ecosystems frequently perish or undergo drastic changes due to the vulnerability of their communities. The larger the island's area, the more diverse the habitats and the greater the species Water/126.html">Diversity of the organisms living there (the so-called "Darlington's rule": a tenfold increase in island area helps double species diversity).

The ratio of immigrant replenishment to mortality establishes a dynamic equilibrium between the number of new colonists establishing themselves on the island and the number of extinct species. Naturalization (establishment) of individual species on the island plays a crucial role in The formation of the insular biota. The success of this process depends on many factors, primarily the eurybiontic Nature of the introduced species themselves. If new species manage to anchor themselves in the new territory, subsequent adaptation of various organisms for coexistence takes place.

Thus, island ecosystems are defined by a Specificity that uniquely unifies their biota. While islands were previously considered in a sense "natural laboratories" of the microevolutionary process—within which speciation mechanisms can be best observed—today opinions are emerging that the principles of new species formation on islands fundamentally differ from mainland ecosystems and cannot be used to study the entire evolutionary process.

Thoughts Out Loud

One way or another, The problem of ecosystem evolution is linked to the extinction of Major Groups of organisms. Obviously, solving this problem is impossible without neocatastrophism, yet even in this case, scientists interpret catastrophes in entirely different ways. Scientific research is significantly complicated by the impossibility of experimentally investigating this issue, without which, unfortunately, natural sciences cannot currently manage. Studying the mechanisms of island biota formation cannot help due to certain differences between general biosphere changes and local transformations, to which the development of life on islands belongs (these processes can occur differently depending on the size and origin of specific islands). Local catastrophes (hurricanes, tsunamis, etc.) demonstrate the exact scale a catastrophe must reach to fundamentally alter The structure of the biosphere.