Lecture 15: Communities: Community Structure Flashcards
basic definition of community
The different species found in one place
what is a more detailed definition of community derived from
an understanding of how it is structured
Research on how communities are structured is _________, and our knowledge continues to develop and advance.
a highly active area of research
Central _____ has revolved around the degree to which cooccurring species are linked in space and time
debate
Historical extremes in the debate:
- interdependent communities
- independent communities
define interdependent communities
The community as a “organism”, evolving as a distinct co-evolving unit
define independent communities
A community as fully disassociated populations of species will have similar environmental needs and tolerances, but do not require each other to survive
modern view of communities
A community is an association of interacting populations, with the interactions maintained via coevolution to varying degrees across space and time.
what is a key pattern in community structure
Species composition changes as we move across the landscape
what do community ecologists want to describe
differences in how species composition changes, and understand the underlying processes
define ecotone
A region of rapid replacement of species along an ecological gradient (temperature, nutrient, water availability, etc.).
the two extreme ecotones
- closed community
- open community
define closed community
- Clustering, or overlapping of species distributions along an ecological gradient, such that there are distinct transitions in groups of species at ecotones
- zonation is present
define open community
- The distribution of any one species does not coincide closely with any other species along an ecological gradient
- weak or no ecotones
what is the first key step in understanding the processes that structure communities
Quantifying how the number of species within a communities changes from place to place
define species richness
- the number of species in a community
- it is the simplest measure of community structure, but often one of the most revealing
how is species richness often the most revealing measure of community structure
substantial variation can exist from place to place that reveals something about the broader processes shaping biodiversity
what does greater habitat diversity provide
it provides more niche space and resources
for species to coexist
define trophic level
Different points on the food chain of consumer resource feeding relationships.
define primary producers
The plants and other autotrophs (self-feeding, photosynthetic organisms) that form the base of the food chain
define primary consumers
- Consumers of primary producers
- herbivores/ detritivores.
define secondary consumers
- Consumers of primary consumers
- carnivores.
Feeding relationships are not really a “food chain”, they are a ________ of interactions
complex web
define food web
- The interconnected network of consumer and resource species within a community
- Few consumer species eat only one resource species, so most species have more than one link in the food web
define omnivory
Feeding on more than one trophic level
_______and more ______ add complexity to a food web
- Omnivory
- trophic levels
what can change competitive dynamics and coexistence
When one consumer controls a resource species that would otherwise be competitively dominant, loss of the controlling consumer can change competitive dynamics and coexistence.
define keystone consumers
Consumer species that maintain diversity and
coexistence among resource species at lower trophic levels
what is the result of the loss of keystone consumers
results in documented “ecological collapse” of communities
At the community level, consumers can ________, and producers in a trophic level can ________
- depress trophic level below
- limit the trophic level above
define top-down control
when a higher trophic level controls the size of the trophic level below it.
define bottom-up control
When the size of a trophic level is determined by the rate of production in the resource species in trophic level below
define trophic cascade
When the indirect effects of consumer-resource interactions extend through other trophic levels
Cascades can be relatively linear or work via ________ of indirect effects - cascades through the whole food web.
complex network
Direct effect
An interaction between two species that does not involve other species.
Indirect effect
An interaction between two species that involves one or more intermediate species
