FACTORS INFLUENCING THE STRUCTURE OF

COMMUNITIES

The fundamental niche constrains community

structure

Ecological Niche- refers to the role of organism to the environment

• Fundamental Niche• Realized Niche

All living organisms have range of environmental conditions under which they can successfully survive , grow and reproduce

Species interaction are diffuse

One reason such experiments tend to underestimate the importance of species interactions in communities is that such interactions are often diffuse, involving a number of species.

Pollination

Diffuse interactions, where one species may be influenced by interactions with many differentspecies, is not limited to competition.

Food webs illustrates indirect interactions

• Food webs also illustrate a second important feature of species interactions within the community: indirect effects. Indirect interactions occur when one species does not interact with a second species directly, but instead influences a third species that does directly interact with second

several of the mussel and barnacle species that were superior competitors excluded the other species and reduced overall diversity in the community. This type of indirect interaction is called keystone predation.

apparent competition occurs when a single species of predator feeds on two prey species .When the predator species is absent, each population of the two prey species is regulated by purely intraspecific, density dependentMechanisms.

The structure of food chains suggests that the productivity and abundance of populations at any giventrophic level are controlled (limited) by the productivity and abundance of populations in the trophic level below them. This phenomenon is called bottom-up control.

Plant population densities control the abundance of herbivore populations, which in turn controlthe densities of carnivore populations in the next trophic level. However, as we have seen from the previous discussion of predationand food webs, top-down control also occurs when predator populations can control the abundance of prey species

Species interactions along environmental gradients involve both stress tolerance and competition

Adaptations of plants to variations in the availability of light, water, and nutrients result in a general pattern of trade-offs between the characteristics that enable a species to survive and grow under low resource availability and those that allow for high rates of photosynthesis and growth under high resource availability

Environmental heterogeneity influences community diversity

• Heterogeneity in the soil environment of prairie communities caused by the borrowing of small mammals results in small-scale variations in plant species composition.