Chapter 6 - Interspecific Competition (CHAPTER) Flashcards
slides notes are PARTIALLY included!!
Interspecific Competition
One species suffers in fecundity, survivorship or growth as exploitation of resources or interference by individuals of another species
- when studying theres a difference between what a process can do vs what it does do.
Competition amongst phytoplankton for phosphorus
Measured the phosphorus impact + population density over time
- Species alone: steady growth + phosphorus decrease
- Two species: one survivor
- The more effective exploiter of the limiting resource
Coexistence and exclusion of competing salmonid fishes
Temperature-mediated coexistence.
General Importance point 1
Competing species often coexist at once spatial scale but are found to have distinct distributions at a finer scale of resolution. (own zone, same stream.)
General Importance point 2
Species are often excluded by interspecific competition from locations at which they could exist perfectly well in the absence of interspecific competition.
General Importance point 3
Difference between fundamental and realised niche.
General Importance point 4
Experimental manipulation is required to know what’s going on in nature.
Fundamental niche
Combination of conditions and resources that allow that species to exist, grow, and reproduce when considered in isolation.
The largest ecological niche that an organism or species can occupy in the absence of interspecific competition and predation
Realized niche
Combination of conditions and resources that allow species to exist, grow, and reproduce in the presence of specified other species that might be harmful to its existence–especially interspecific competitors.
: that portion of its potential (fundamental) niche occupied by a species when competitors or predators are present
Niche differentiation
Differential resource utilization
- Using slightly different resources in slightly different ways.
Coexistance of competing diatoms
Two limiting resources that limit growth
More of one and one species was better than the other.
Sufficient supply allowed coexistence.
Competitive exclusion principle (or Gause’s principle)
If two competing species coexist in a STABLEEEE environment, then they do so as a 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.
Established by mathematical model of interspecific competition (Lotka and Volterra.)
Competitive exclusion principles problems
Competitive exclusion principle does not say that whenever we see coexisting species with different niches, it is reasonable to jump to the conclusion that this is the principle in operation.
All species have unique niches.
Niche differentiation does not prove coexisting competitors.
Species may not be competing at all.
Although species may not be competing now, maybe their ancestors were in the past. So mark is left imprinted by evolution on their niches, behavior, or morphology.
Must also question the word “stable”
Environmental heterogeneity (spatial heterogeneity in environmental conditions.)
Spatial and temporal variations in environments
Interspecific competition proceeds not in isolation, but under the influence and constraints of a patchy, cyclical, impermanent and unpredictable world
Proves that the competitive exclusion principle is far from the whole story, when it comes to determining the outcome of an interaction between competing species.
- Ants in acacia trees in kenya.
- Trees become naturally available for recolonization due to damage, fire, or drought.
- Recolonization patterns were different from the original competitive hierarchy.
- The continuous tree swaps allow for coexistence.
A competition-colonization “trade-off”
when one improves, it tends to be at the expense of the other.
An inferior competitor could be able to coexist with a superior competitor that would rapidly exclude it from a continuous, homogeneous environment.
Four terrestrial plants
Seeds placed at random or single-species aggregations.
The mixture showed that co-occurrence of species in a constant, homogenous environment would probably exclude one another. It’s too variable for competitive exclusion to run its course.
Invoking the ghost of competition past.
Adverse effects of interspecific competition may have favored those individuals who managed to avoid those competitive effects.
- Coexisting species, exhibit differences in habavior, physiology, or morphology ensuring little competition.
- Coexisting present-day competitors and avoidance of competition can look the same
Character displacement
A morphological response to competition from another species.
A measurable physical difference between two species which has arisen by natural selection as a result of the selection pressures on one or both from competition with the other
Ecological release
A response to the absence of ecological effects of other species. Usually a population increase/explosion.
Sympatry
living in the same place.
Testing interspecific competition with bacteria
Use competing strains of same species that dont interbreed, but can fail to show whole-organism effects because its more similar to INTRAspecific
Interspecific competition can therefore either keep apart (6.2), or drive apart(6.3) the niches of coexisting competitors.
The more limiting resources the more coexisting competitors.
The environmental heterogeneities and absences of equilibria in natural systems mean that coexisting competing species may exceed the number of different resources available to them.
Niche complementarity
species differ in their resource use (niche differentiation) and facilitate each other.
A guild
Group of species that exploit the same class of environmental resource in a similar way.
Competitors may exclude or coexist if there is ecologically significant differentiation of their realized niches.
Or evolution could just not do either if environmental heterogeneity prevents it.
Evolution can drive niches of competitors apart until they coexist but no longer compete
All of this may express itself at ecological community level.
Imact of interspecific competititon on human activity
direct
The prevalence of current competition
It is widespread., 90% studies demonstrated interspecific competition.
- With one species = 90%
- With more species = 50%
The surveys may have also exaggerated the true frequency of competition.
Prediction of niches of competing species differentiation
Interspecific competition predicts that the niches of competing species differ MORE than would be expected from chance alone
Neutral/Null models.
Data rearranged into a form representing what the data would look like in the absence of interspecific competition.
–> This way if the actual data shows significantly statistical difference from the null model , then interspecific competition can be inferred!
Interspecific Competition definition
Competition for resources between members of different species
Quick example of interspecific competition
The Japanese oyster has been introduced in the Netherlands in the 1970s
It has outcompeted the indigenous oyster in most places
It is a strong competitor for food and space
Easy test for interspecific competition
remove one species from the plot of the area, see if it effects the other species
Niche differentiation
Resource partitioning: species living in the same habitat using the same resources
- spatial separation of resources
- temporal separation of resources
- different response to conditions
Competition and past evolution
During evolution of a species, competing species may have been a selection force
Selection may have favoured individuals that avoided competition
Coexisting species will exhibit differences (in behaviour etc.) that insure they will compete little or not at all
Resource competition theory
the more limiting resources, the more coexisting competitors
Niche complementarity
The tendency for coexisting species which occupy a similar position along one niche dimension, to differ along another.
Interspecific competition in practice
What is the prevalence of current competition in reality?
- In a large % of the studies, interspecific competition was found
- However, pairs of species may be chosen because competition was expected
- Studies were competition was absent were possible not reported
