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BIOL 121 Lecture Notes - Interspecific Competition, Competitive Exclusion Principle, Ecological Niche

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BIOL 121
Carol Pollock

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Biol 121 225
Freeman 1196-1209 (Ch. 53) Jan. 13, 2010
Define community
-interacting species living within a defined area
How can species interact in
-species in a community interact constantly
-members of different spp (species) eat one another, pollinate each other, exchange
nutrients, compete for resources, and provide habitats for each other
-therefore, fate of a population may be tightly linked to other species that share its
Define fitness and describe how
biologists focus on it to study
species interactions.
-to study species interactions, biologists focus on analyzing effects on the fitness of
the individuals involved
-fitness is the ability to survive and produce offspring
-does the relationship b/t two species provide a fitness benefit to members of one
Four categories of interaction
-/- means competition
+/- consumption and parasitism
+/+ mutualism
+/0 commensalism birds feeding on insects that ants drive out
What do species interactions
-species interactions may affect the distribution and abundance of a particular
-e.g. predation, disease, competition
-changes in species interactions often explain short-term changes in population
What does species interactions
have to do with natural
-species act as agents of natural selection when they interact for e.g. deer are fast
in response to natural selection exerted by their major predators like wolves, which
then favours fast wolves with good sense of smell and eyesight
-in biology, a coevolutionary (species influence each others’ evolution) arms race
occurs b/t predators and prey, parasites and hosts, etc.
How can the type of interaction
-outcome of interactions among species is dynamic and conditional
-e.g. in commensal relationship b/t birds and ants, if bird attacks force some insects
into path of ants, then becomes mutual
-if birds begin to take prey that would otherwise be taken by ants, then parasitism
-outcome of interaction may depend on number and types of prey, bird, and ants
present, and may change over time
-/- interaction that occurs when diff. individuals use same resources and when those
resources are limiting
-related to theory of evoluation by natural selection
-individuals that are more successful in competition leave more offspring than
others they are fitter
-if traits that lead to success are heritable, then fq of alleles in pop changes
Intraspecific vs interspecific
-competition b/t members of same species is intraspecific, vice versa
Types of competition (6)
-consumptive individuals consume same resources like trees consuming water
-pre-emptive one species makes space unavailable to other species
-overgrowth one species grows above another (plant taking sunlight)
-chemical one species produces toxins
-territorial mobile species protects feeding/breeding territory
-encounter two species interfere directly for specific resources (hyena vs vulture)
-niche is the range of resources that the species is able to use or the range of
conditions it can tolerate
-interspecific competition occurs when the niches of two species overlap
Competitive exclusion principle
-hypothesis that species with the same niche cannot coexist
-asymmetric competition one species suffers a much greater fitness decline than
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