Ecology: the biology of interaction. 3.10. Nature and characteristics of communities
{"title":"","summary":"","body":"Naturally, the most vivid and interesting part of ecosystems are communities — the assemblages of their living components. Are communities clearly distinct separate objects? Occasionally — yes, more often — no. The debate is still unresolved. Communities can be characterized by a number of ..."}
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3.09. Trends in Successions
D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Section 3. Biogeocenology and Ecology of Communities
3.11. Trophic Relationships and Levels
{ "title": "3.10. Nature and Characteristics of Communities", "summary": "", "body": "Obviously, the most vivid and interesting part of ecosystems are communities — sets of their living components. Interactions between individuals of different species and populations occur precisely within communities. Some of these connections form quite intricate chains. Let's give just one example that has long become a classic.\n\n\"Darwin discovered that bumblebees with their long proboscis — the only insects capable of pollinating the deep tubular flowers of red clover. From this, he concluded that the spread of red clover in England is explained by the abundance of bumblebees. At the same time, referring to one of the entomological works, he points out that bumblebee nests are most often found near cities and villages, where they are less destroyed by voles that eat larvae and pupae. Why are there few voles near cities and villages? Because there are many cats that significantly reduce the population of voles. A German scientist continued this reasoning as follows: if it is proven, he said, that cats are responsible for the prevalence of clover in England — the main food of cattle, and clover is ecologically related to the British naval fleet, since beef is the main food of sailors, then, therefore, cats have the main merit in Britain being a great naval power. The next step was taken by Thomas Huxley: he argued — partly in jest — that since cats in England are mainly kept by old maids, then British power can be logically — and ecologically — deduced from the \"cat-love\" of numerous English old ladies\" (P. Farb, 1971).\n\nAs a result of joint evolution, different parts of the community adapt to each other. As a result, many types of communities have a characteristic species composition and a well-defined ratio of organisms belonging to different ecological groups.\n\nAre communities clearly distinct separate objects? Rarely — yes, often — no. At the beginning of the 20th century, a discussion about the nature of communities flared up between American ecologists. F. Clements and other supporters of the organismic concept of ecosystems considered communities as superorganisms. On the contrary, H. Gleason and other supporters of the individualistic concept considered communities as conglomerates of species with similar requests to the environment.\n\nThe dispute has not been resolved so far. On the one hand, gradient analysis (i.e., the study of the distribution of species along gradients of change in some significant, primarily climatic, factors) showed that the boundaries of the distribution of individual species do not necessarily coincide with the boundaries of communities (Fig. 3.10.1 and 3.10.2). The steeper the gradients of conditions, the clearer the boundaries of the distribution of species. The boundaries of the distribution of dominant species are more characteristic than the boundaries of the distribution of random species. On the other hand, since communities have the ability to self-regulate, their boundaries are arranged quite complexly and cannot be reliably determined using gradient analysis.\n\n[IMG_1]\nFig. 3.10.1. Theoretical curves showing possible options for changing the occurrence of species along a gradient (smooth change) of some essential factor\n\n[IMG_2]\nFig. 3.10.2. Actual curves of occurrence of various tree species depending on the gradient of humidity. The recorded curves do not correspond to any of the theoretical options shown in Fig. 3.10.1\n\n\"On the nesting territory of a pair of great spotted woodpeckers (Dendrocopos major L.) in a suburban oak forest, there are hundreds of tree trunks of several species, thousands, if not tens of thousands of stems of herbaceous plants of dozens of species (strictly speaking, one or several plant associations can be distinguished on this territory); each trunk is a habitat for dozens and hundreds of individuals of several species of xylophagous insects and thousands of individuals of phytophagous insects feeding on green mass, flowers and fruits; herbaceous plants form habitats for tens of thousands of phytophagous insects and thousands of individuals of their predators; in the forest litter and upper soil horizons, there are thousands and tens of thousands of individuals of dozens of species of insects (predators, saprophages, coprophages), centipedes, arachnids, terrestrial crustaceans, worms, and the number of species of microorganisms (bacteria, fungi, protozoa) living in the soil is counted in tens, if not hundreds of millions. In addition, in addition to a pair of woodpeckers, one or two pairs of nuthatches (Sitta europaea L.), several pairs of great tits (Parus major L.), flycatchers-white cheeks (Ficedula albicolllis (Temm.), robins (Erithacus rubecula L.), chaffinches (Fringilla coelebs L.), warblers-treshotkas (Phylloscopus sibilatrix Viell.), and for a predator like a goshawk (Accipiter gentilis L.), this territory may be only a small part (from 1/25 to 1/10) of its nesting and hunting territory. The same territory is occupied by a dozen individuals of shrews (Soricidae) and mouse-like rodents (Muridae), one squirrel (Sciurus vulgaris L.) can feed, and for a weasel (Mustela erminea L.) or a ferret (M. nivalis L.), as well as for a hawk, this territory is approximately 1/10–1/5 of their foraging territory, not to mention large ungulate mammals (moose (Alces alces L.), roe deer (Capreolus capreolus L.), wild boar (Sus scrofa L.)), for each individual of which a territory of hundreds of times larger is needed and which can also be detected on this territory if the area of the forest is sufficiently large or it is connected to neighboring arrays\" (Yu. I. Vergeles, 2000).\n\nProbably, the community still represents a real ecological unit. The functioning of the community consists of the activities of its constituent individuals, but represents something more than its sum. The efficiency of the community and its stability increase in proportion to how well-coordinated, evolutionarily \"fitted\" populations constitute it. An example of the importance of the \"fitting\" of species in the community to each other is the reaction of communities to introducents (invaders). Most often, introducents cannot join the composition of integral communities and die out, but sometimes they give outbreaks of numbers, changing the functioning of communities.\n\nCommunities can be complete (including producers, consumers, and reducers) and incomplete.\n\nCommunities can be characterized by a number of features, considering their emergent properties that are absent at the level of parts of the integral system. Some of them are as follows.\n\nCommunity composition (species structure) — species that make up the community. Often the appearance of a community is determined by some basic (or several basic) species. Such species are called edificators. Usually, around individual individuals of edificator species, a complex of species closely associated with it — a consortion — develops. Consortia are structural units of communities.\n\nAbundance — the number of individuals per unit area or volume.\n\nSpecies frequency — the proportion of individuals of a certain species to the total number of individuals.\n\nDiversity — species richness. It is higher, the more species, and lower, the more individuals of each species are found in a separate sample.\n\nSpatial structure — features of the arrangement of individuals relative to each other. Vertical structure, or stratification, and horizontal — mosaicism are distinguished. Stratification is characteristic of phytocenoses, consisting of plants of different heights. An example of stratification in a forest: I — trees of the first magnitude (spruce, pine, oak, birch, aspen); II — trees of the second magnitude (rowan, cherry); III — undergrowth of shrubs (hazel, euonymus, cherry); IV — undergrowth of tall shrubs and large herbs (Ledum, blueberries, heather, aconite, Ivan-tea); V — low shrubs and small herbs ( Vaccinium, cranberry, oxalis); VI — mosses, epiphytic lichens, liverworts.\n\nEcological structure — the ratio of basic ecological groups of organisms, as well as various life forms.\n\nPeriodicity — daily, seasonal, long-term, age-related." }
3.09. Trends in Successions
D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Section 3. Biogeocenology and Ecology of Communities
3.11. Trophic relationships and levels