WEC - Interspecific competition (CH6)

Example of types of growth with the Lotka-Volterra model

* Alfa is a negative effect that reduces the growth of a species (see blue parabole).

Fundamental niche

Niche without competing species

Realized niche

Niche with competing species

Conditional portioning

Animals avoiding each other by behaviour; e.g. being diurnal or nocturnal.

Resource partioning

Animals avoiding competition by resource use; e.g. eating different things.

Ecological released

Species removed from an ecosystem

niche complementarity

(no overlap in competition/resources/behaviours between animals.

The competitive exclusion principle

* If two competing species coexist in a stable environment, then they do so as a result of niche differentiation.
* If, however, there is no such niche differentiation, or if it is precluded by the habitat, then one competing species will exclude the other



It can depends who is the weaker competitor; e.g. when the weaker competitors are more resistant to malaria, it can still exist among the stronger competitor à parasite impacts competitive outcome.

Niche

the match of species to a specific environmental condition. It describes how an organism/population responds to a distribution of resources and competitors and how it turn alters those same factors.

Ecological niche

 the specific place where the needs/resources/conditions of the animal are met. So an ecological niche is not a place or habitat, but it is more about:

o   Species

o   Tolerances and requirements

o   Environment

o   Conditions and resources.

Also, it is a concept which describes how rather than where a species lives à not necessarily a natural environment, zoos can also be an ecological niche. Finally, ecological niches are multidimensional.

__Parasite-mediated competition__

* Can have a negative outcome: one species outcompeted, where two would have otherwise co-existed \n Example: squirrels in the UK
* Can have a positive outcome: two species co-exist, where one would otherwise have been outcompeted Example: anole lizards in Sint Maarten

__The competitive exclusion principle:__

* If two competing species coexist in a stable environment, then they do so as a result of niche differentiation. à however, environments are rarely stable; environmental heterogeneity tempers interspecific competition.
* Competition-colonization ‘trade-off’
* Aggregated distribution allows co-existence
* If, however, there is no such niche differentiation, or if it is precluded by the habitat, then one competing species will exclude the other.



Note:

* Competitive exclusion is difficult to prove à Remove species and see if the other species expand.
* Ghost of Competition Past: it could also be that older, now non-existent species did compete with the animals, resulting in competition, but that there is no competition nowadays.

Dogma 1: Nature is in balance



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* No, there are often (a)biotic disturbances.
* So, there is potential for competition, but disturbances prevent resources from becoming limiting.

Dogma 2: Species abundance and distribution patterns are regulated by deterministic factors

* There is no competition, interactions are neutral. It is not about the fittest, but about the luckiest: so who came first?
* Difficult to disprove this theory.

Dogma 3: Competition

There is no competition, but facilitation à e.g. how can zebra and wildebeest not compete even though they eat the same? This is because they eat the grass differently; zebra eats thougher grass and wildebeest the rest.

Types of competition:

* Interference competition = When one organism physically restricts another organism's access to resources (e.g. by spatial terretories).
* Exploitation competition = indirectly competing with each other.

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Lotka-Volterra model:.

Model that describes the interactions between two species in a predator-prey relationship. It assumes that the population growth of each species is limited by the other's population size. The model predicts that the two populations will oscillate around a stable equilibrium.

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How to determine alpha and beta in the Lotka-Volterra model?

Alpha = beta/alpha

Beta = alpha/beta

Under what circumstances does a species increase or decrease in the Lotka-Volterra model?

* Blue line represents equilibrium: growth is 0. Under the line there is species growth, above is species decline.
* Red line represents carrying capacity. Under the red line there is still carring capacity and above it is above the capacity.
* Then we can combine the graphs to create an overview.

Lotka-Volterra model outcomes

* Two parallel lines: the species with the line above will win and outcompete the other.
* Two lines that meet: all lines point to the blue dot; this is the equilibrium between the two species.
* Two lines that meet: all lines move away from the white dot; unstable equilibrium.

Main points about competition

* Competing species often coexist at one spatial scale but are found to have distinct distributions at a finer scale of resolution. Here, the fishes coexisted in the same stream, but each was more or less confined to its own altitudinal zone (which had different temperatures).
* Species are often excluded by interspecific competition from locations at which they could exist perfectly well in the absence of interspecific competition.
* We can describe this by saying that the conditions and resources provided by the white-spotted charr zone are part of the fundamental niche of Dolly Varden charr.
* Thus, a species’ fundamental niche is the combination of conditions and resources that allow that species to exist, grow, and reproduce when considered in isolation from any other species that might be harmful to its existence; whereas its realized niche is the combination of conditions and resources that allow it to exist, grow, and reproduce in the presence of specified other species that might be harmful to its existence—especially interspecific competitors.

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Niche differentiation allows…

Allows competitors to co-exist

Competitive Exclusion Principle or Gause’s principle

* If two competing species coexist in a stable environment, then they do so asa result of niche differentiation.
* If, however, there is no such differentiation, or if it is precluded by the habitat, then one competing species will eliminate or exclude the other.

competition-colonization ‘trade-off:

A phenomenon in ecology where species compete for resources in a given area, but also have the ability to colonize new areas for resources. This leads to a trade-off where species must balance their energy between competing and colonizing.

* when one improves, it tends to be at the expense of the other),

(character displacement:

a morphological response to competition from another species),

niche complementarity.

That is, niche differentiation in a community of species involves several niche dimensions, with fish species occupying a similar position along one dimension tending to differ along another dimension, be it species of anemone, zone on the shore, or food particle size (reflected in the size of the fish).

A guild

a group of species that exploit the same class of environmental resource in a similar way