BIO2129 topic 11
biotic factors influence the
distribution and abundance of organisms
interspecific and intraspecific interactions affect
individuals and the abundance of populations
what are the types of biotic interactions
interspecific and intraspecific
what are some times inter/intraspecific intercations
competition, mutualism, predation, herbivory, parasitism
What is intraspecific competition
between members of the same species.
Interspecific competition
between members of different species.
when does inter/intraspecific competition occur
when organisms compete for limited resources like food, light, space, or mates.
Long-term interactions between different species (interspecific) can have
major ecological and economic consequences. EX. in forestry and fisheries.
example of long-term interspecific interactions and how they shape ecosystems and economic effects for humans
Forest. In dense forests, light is a limited resource; because of this, species compete with each other for sunlight, nutrients and space.
intra/interspecific competition comes in two main forms
resource competition (exploitation) and interference competition
what is resource competition (exploitation)
when a resource is limited in supply and individuals indireclty compete to use it up. Ex trees absorbing light.
resource competition leads to slower
growth and reduced survival/reproduction when resources are scarce
what is interference competition
direct harm or confrontation between individuals. EX. lions fighting over territory or mates.
interference competition is
uneven impact, one individual may gain more access to resources than others. (aggression, territorial or preventing others form getting resources)
resource competition is due to
niche overlap (when two species/individuals rely on the same limited resource)
what is a niche
the set resources an organism can use to survive and reproduce in its environment
a niche can also be called
Hutchinsonian
competition determines
which species can persist in an environment. some can be outcometed or excluded from certain habitats
what is a fundamental niche
full range of conditions/resources a species could use
what is a realized niche
what the species actually uses, after competition limits it
competition between species creates differences in
fundamental and realized niches of a species
how does Connell's barnacle experiment support competition affecting biotic interactions
he studied two species. Balanus grows faster and takes over the lower part of the shore, where it stays wet most of the time. Chthamalus lives higher up, where it’s drier. When Connell removed Balanus, Chthamalus was able to grow lower down the rocks too. This showed that Balanus was outcompeting Chthamalus and forcing it to live higher up. So the environment (like dryness) set the upper limit, but competition set the lower limit of where Chthamalus could survive.
what is the competition exclusion principle
two species with identical niches cannot coexist since one will eventually outcompete the other
competition exclusion principle is also called
theory of limiting similarity
in the theory of limiting similarity if two species' niche overlap is too large
one species is driven to extinction or displacement
why does niche overlap cause exctinction/displacement
due to competition for identical resources
the lotka-volterra competition model builds on
logistic growth to describe competition between species (interspecific)
what is logistic growth
population growth that slows as it reaches carrying capacity (K)
competition is only a
negative affect
the logistic growth effect of a competition is
to slow population growth and reduce max population size when competitors are around
the coefficient (a) converts individuals of one species into
their equivalent impact on the other species (how much one species counts as another in resource use. EX deer and moose)
Lotka-volterra equations assume
1) no immigration/emigration. 2) stable age structure, birth/death rates are constant 3) genetic factors constant (no evolution/adaptation) 4) no time lags (population responds instantly to change) 5) K doesn't change 6) logistic growth 7) linear competition
the lotka-volterra competition model predicts
directions correctly (who wins/loses) but not the exact timing or complexity of real interactions
in the real world the Lotka-Volterra model is an oversimplification because
real ecosystems have environmental variation, migration, adaptation, and many species instead of just two
despite being simple Lotka-Volterra is useful because
its a foundation for how competition works and inspired more complex models that include evolution, environmental change and resource dynamics
a species with a lower R is a
better competitor because it can persist even when resource are scarce
what is Tilaman's mechanistic model of resource competition
that the most successful competitor is the one that can reduce the availability of a limiting resource to the lowest level (R) while keeping its population
R is equal to
the minimum resource level required for a species to survive and reproduce
how is Tilmans model differenct from lotka volterra
it describes the mechanism (how resource use and availability drive competition) not just the population outcome
what's the difference between both models
The Lotka–Volterra model explains how competition affects population growth, while the Tilman model explains why competition occurs through the depletion of shared resources.