Lecture 9 + 10 Flashcards
Competition between individuals of the same species is which type of competition?
Intraspecific competition
A single algal species competes for a required resource, silicate. As the number of individuals increases, there is less silicate available for the original individuals. This is an example of:
Exploitation (competition)
Snowy plovers, a coastal bird species, are found to live only on sandy beaches. Where snowy plovers live is referred to as their:
Habitat
Competition between individuals of the same species can have effects on their
- survival
- growth
- reproduction
- access to mates
For any given species, there is a _______, which describes the niche that occurs under normal circumstances of interspecific competition within a community and typically differs from the hypothetical ______, which describes the niche that the species would inhabit if interspecific competition was removed.
realized niche, fundamental niche
The Competitive Exclusion Principle states that
If two competing species coexist in a stable environment, then they do so as a result of niche differentiation
Six types of species interactions
- amensalism
- commensalism
- competition
- exploitation
- mutualism
- neutralism
The six types of species interactions are based on how 2 species influence each other’s fitness
A negative, positive, or no effect on another species.
Example of exploitation
+/-
A spider eats a fly
Example of competition
-/-
A sparrow and a cardinal eat the same seeds
Example of mutualism
+/+
A butterfly and a flower
Example of neutralism
0/0
Two species that don’t influence each other
Example of commensalism
+/0
A vulture eats the scraps of a lion’s kill
Fungi on dead trees
Example of amensalism
-/0
A flower is stepped on by an elephant
Frog calls affecting an owl’s ability to hear prey/mice
Competition
Can be for any limited resource (ex. mates, locations, food, etc.)
It is a -/- interaction, it is not like sports
- there are costs to competition energetic expenditure, time, risk of injury, etc.
Pizza arrives at a party and those individuals who randomly smell and find the pizza first will get the pizza and some people will go hungry. What type of competition is this?
Intraspecific competition and exploitation competition
- however, not technically a species interaction
- not the same as an +/- exploitation interaction; this is a form of competition based on exploiting resources
At a pizza party, you drop your pizza but a cute dog prevents you from getting the pizza. What type of competition is this?
Interspecific competition
Interference competition
At a party, someone else flirts with your potential mate. What kind of competition is this?
Intraspecific competition
Interference competition
Intraspecific competition
Occurs among individuals of the same species
Interspecific competition
Occurs between individuals of different species
Exploitative competition (resource or scramble competition)
Competition between individuals by reducing availability of shared resources
Interference competition (contest competition)
Direct competition between individuals for scarce resources by one impeding or denying access to the resource by another
Competition
As population size increases intraspecific competition typically becomes greater.
This also applies to interspecific competition (the -/- interaction). If there are many individuals of a competitor species around, it can reduce fitness.
Competition over resources
Resource utilization curves
ex. small ground finches eat small seeds, medium eat medium seeds, large eat large seeds. Three different resource curves: seed depth (mm) x diet proportions
No competition curves
2 curves don’t touch, side by side
Low competition curves
2 curves overlap a little
Medium competition
2 curves overlap more
High Competition
2 curves almost overlap completely
Competitive exclusion
When 2 species are very similar, they may not be able to coexist because competition is so strong.
One species may consume all the resources leaving little for the other.
If 1 species is a poor competitor, it can go locally extinct.
If 2 species are very similar, one may randomly go locally extinct.
Gause’s experiments
Both species of single-celled organisms thrived when grown individually.
Highlights exploitative competition – P. aurelia outcompeted P. caudatum for resources
However, Gause found that by tweaking environmental factors like type of food, he could create conditions where the two organisms co-habited.
-> led to competitive exclusion principle
Bar graph to show average fitness when species are separate (two different sizes of gerbils)
Individual fitness around the same, medium height
Bar graph to show average fitness when species are together (two different sizes of gerbils)
Smaller species fitness is low, bigger species fitness is high
-> competition can be relatively symmetric or asymmetric
With the gerbils, why is this the pattern we find?
Larger species has a strong negative impact on smaller ones because larger ones are a dominant competitor (dominant interference competitor).
The competition is asymmetric.
The larger species are not “good for” smaller ones. Competition reduces fitness.
Fitness when species are together
While larger species has higher fitness, it is still lower than individual fitness when the species are separate.
If we put both larger and smaller species together in a 100x100m area in the desert. What will happen after 50 years?
The two species of gerbils would coexist.
How can the two species of gerbils coexist? Why don’t the larger ones drive the smaller ones extinct like the 2 species in the paramecium example?
Time has been insufficient to allow exclusion
There is immigration
The environment is temporally variable
The environment has spatial variation
There are multiple “resources”
-> maybe the smaller gerbils are better at harvesting seeds at low density
Resource use when small and large gerbils are together
Small gerbils: upside down parabola, specializing in lower patch seed density
Large gerbils: upside down parabola, top part almost flattens out, trailing down, better at higher patch seed densities
Patch seed density v. proportion use
To coexist with other species, a species needs to be the best at:
Something, sometime, somewhere, somehow, etc.
- they need their own niche
The niche concept
The range of environmental conditions and resources within which individuals of a species survive, grow, and reproduce.
Resource utilization curves
Resource gradient v. intensity of resource utilization
Both bell curves, width is niche breadth, the overlap between the two curves is called the niche overlap.
The distance between the max of bell curve is called the niche separation.
-> narrow niche breadth = specialist
-> wide nich breadth = generalist
The idea of niche dimensions
One dimension (ex. temperature) is one parallel line.
Two dimension (ex. temperature and humidity) is a rectangle. Temp on x axis, precipitation on y axis
Three dimensions (ex. temperature, humidity, and soil grade) is a cube. Soil grade axis goes out like a cube.
Which scenario is most plausible?
- a penguin lives in the rainforest
- a white-tailed deer lives in the desert
- a lion lives in the tundra
- a clownfish lives in fresh water
None of the above!
The niche as an n-dimensional hypervolume
The concept of the niche based on a species tolerance and use of a series of n environmental factors and resources.
Can define multiple (n) biotic and abiotic resource axes, each utilized with a certain frequency distribution.
Fundamental niche
The full hypervolume or range of environmental factors permitting a species to survive and reproduce (think abiotic)
Graph on curve is half a bell curve flattening out at the top
