Lecture 7 & 8 Niche, competition and community structure Flashcards Preview

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what is the n-dimensional hyperspace?

A concept that is the cornerstone of ecological thought. Considers the niche of an organism in all conditions and things it needs. (Hutchinsons, 1957). where all niche dimensions are accounted for and make a volume of limits to an organism and where it can survive e.g. temp, food, light, altitude etc etc. can compare organisms quantatively.


Fundamental niche

region of environmental space where fitness is greater than or equal to one in the absence of competitors or predators (Hutchinson, 1957). i.e. limits to where an organism can survive


Realized niche

a more restricted region of environmental space than fundamental niche obtained after accounting for biotic interactions. (competition)


Explain the (Gause, 2934) paramecium experiment, (competative exclusion)

P. caudatum and P. aurelia both grown separately & measured, very similar in growth of population density & time.
Grown together in same conditions, was thought a mixture would occur, but not the case. Grew quite happily but then suddenly resources are in short supply e.g. food & P. aurelia drew P.c to extinction.Showed two species with same niche cannot live indefinitely in same habitat without further disturbance (Gause, 1934)


What is the competitive exclusion principle?

2 organisms compete in exact same way only one will survive. If they are slightly different, they can avoid competition in certain areas & can co-exist.


If the realised niche is different (niche differentiation) between two competitors what happens?



What is character displacement?

Where competitors are coexisting and over time their morphology gets selected differently in order to compete less.


Give a summary of basic competition theory

populations often compete for resources
- there’s a limit to population growth
competition between two species
- leads to the elimination of one species by the other
- or they adopt different niches (avoiding complete competition) and can coexist
where species occur together, there are likely to be limits to the similarity of coexisting competitors


Give an example of character displacement

humming birds in costa rica & the flowers they pollinate. The plants compete for the birds. They flower at separate times to avoid competition and coexist, staggering of flowering phenologies.
Darwins finches.
when living together beaks some smaller for smaller seeds and some bigger for bigger seeds.


What are the predictions for basic competition theory?

coexisting competitors should show niche differentiation usually morphological.
potential competitors with little or no nice differentiation are unlikely to coexist - may be negatively associated, where one is the other isn't


Do we actually have any examples of competition?
what are the theories for this question?

1) We are seeing active/current competition
2) Ghost of competition past – we are just seeing what’s left of previous competition
3) It’s all just coincidence


What is competitive release?

occurs when one of two species competing for the same resource disappears, thereby allowing the remaining competitor to utilize the resource more fully than it could in the presence of the first species.


Provide a natural experiment for competition:

Ground doves in New Guinea. 3 species of ground doves 4 different islands. All 3 are shown on one island (New guinea) all in separate habitats i.e. coastal scrub, light forest and rainforest. In Bagabag island the rainforest species is absent and the species living in light forest occupies the rainforest as well. In the remaining islands only 1 species inhabits them and lives in all habitats.


what is a downside of natural experiments?

Different locations may have different conditions and change the species' range.


Give an example of a field experiment illustrating competition

Salamanders. 2 species coexisting. Put them in enclosure separately and 1 together. The salamanders put together faced negative impacts compared to the ones on their own (Hairston, 1980). Direct evidence for competition.


What is a downside of lab experiments?

May not reflect proper conditions.


There has been lots of work on competition in an agricultural sense (weeds). Provide examples for additive and substitutive experiments:

Additive experiment: 1st pot = 10 crop, 2nd pot = 10 crop 1 weed, 3rd pot = 10 crop 2 weed etc

Substitutive experiment: 10 pots, 2 species , 1st pot = 10 crop, 2nd pot = 9 crop 1 weed, 3rd pot = 8 crop 2 weed etc
Run experiments and see how they grow and the yield of crop. Watch the effect of the weed and gradient.


Neutral or null models

Effects of species on each other are null originally and then change bits and bobs to see what would happen
This approach is bound to be of limited use unless it is applied to groups within which competition may be expected (“guilds”)
- ok for comparing different kinds of ducks but not ducks vs hummingbirds
negative aspect - you make assumptions about what is actually competing where there may be other things competing as well that you don’t know about


Apparent competition

when two individuals that do not directly compete for resources affect each other indirectly by being prey for the same predator (Hatcher et al. 2006) Consider a hawk (predator, see below) that preys both on squirrels and mice. In this relationship, if the squirrel population increases, then the mouse population may be positively affected since more squirrels will be available as prey for the hawks.