The structure of ecological communities is influenced by various factors, including the fundamental and realized niches of species, species interactions, and environmental conditions. Species interactions within communities can be direct, such as competition, or indirect, mediated through other species in a food web. Both bottom-up and top-down controls influence population abundances across trophic levels. Environmental gradients and heterogeneity impact species distributions and community diversity through variations in stress tolerance and competition for resources.
3. Ecological Niche- refers to the role of
organism to the environment
• Fundamental Niche
• Realized Niche
5. All living organisms have range of
environmental conditions under which
they can successfully survive , grow
and reproduce
6. 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.
9. Diffuse interactions, where one species may be
influenced by interactions with many different
species, is not limited to competition.
10. 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
12. 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.
14. 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 dependent
Mechanisms.
15. The structure of food chains suggests that the
productivity and abundance of populations at any given
trophic 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 control
the densities of carnivore populations in the next trophic
level. However, as we have seen from the previous
discussion of predation
and food webs, top-down control also occurs when
predator populations can control the abundance of prey
species
17. 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
19. 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.