Lecture 1
What's one example of a life-history trade-off?
more offspring, shorter lifespan, and small adult body size
What is semelparity?
When the animal does not produce for a long time and then gives birth to an enormous amount of babies.
What is the zero-growth isocline?
The lines on the graph that shows zero growth for a species.
What does commensalism mean?
This is when one of the interacting species benefits while the other one just exists, not benefiting or being damaged.
What does it mean to have a
(dN)/(dt)
that is greater than zero? Less than zero? Can it ever be equal to zero?
Greater than zero: population has an exponential growth.
Less than zero: exponential decay
It can be zero is the population size is stable; deaths are equal to births.
What are the goals of density-dependent vs. density-independent species?
Density-independent species want to increase the number of species no matter what.
Density-dependent species focus on making the babies survive as well as possible.
In graph 2, what direction would the arrow be pointing if you start in between the two isoclines?
The arrow would be pointing down to the right, resulting in a stable equilibrium at the Ks.
What is the difference between a realized niche and a fundamental niche?
A fundamental niche is the entire range of habitat that a species can occupy, and a realized niche is the portion of fundamental nich a species actually occupies.
Looking at the three demographic graphs, which shape depicts a relatively stable population? Growing population? Declining population?
Stable: wider in the bottom and slowly gets smaller as we go higher.
Growing: wide at the bottom and tapers at the top.
Declining: smaller at the bottom than at the top.
What is the difference between density-independent and density-dependent predation? Give an example of both species
Density-independent predation: the rate of predation is unrelated to the size or density of the prey. ex: plankton and filter feeders
Density dependent predation: when the rate of the rate of predation changes based on the density of the prey population. ex: rabbits and wolves
What is the difference between a stable and an unstable equilibrium?
Stable equilibrium is when the population returns to their balanced state if distubance happens. There would be no competition between the 2 species, there would either be one or they both coexist.
Unstable equilibrium is when the population does not return to its balanced state if disturbances happen.
How do insects derive a fitness advantage from using highly toxic host plants?
Insects, such as monarch butterflies, store the toxic extract from the host plant and use it as a self-defense mechanism.
In life-history trade-offs, increasing both offspring number and offspring size is constrained by a key biological principle.
a. What is this constraint, and why does it limit simultaneous increases in both variables?
b. Under density-independent ecological conditions, explain how a species might evolve to produce smaller offspring, even though natural selection does not directly favor smaller offspring.
a. finite resource availability
b. Density independent species focus on producing higher number of offspring to increase their chance of survival. Evolving to produce smaller offspring happens because you have to allocate your resources either to offspring number or size, if you allocate it to number, then the size would be smaller.
Define r-selected traits, provide examples of species that exhibit these traits, and describe ecologies that are largely density-independent and explain how they favor r-seleced traits.
Define K-selected traits, provide examples of species that exhibit these traits, and describe ecologies with strong density dependence and explain how they favor K-selected traits.
r-selected traits:
- r-selected traits maximize the reproductive output; they have smaller adult body size, larger number of species, and shorter lifepans. ex: insects
- their ecologies would have frequent disturbances, requiring them to produce many offspring quickly so there could at least be some of them who survive and not die because of the siturbances.
K-selected traits:
- they have traits that prioritize survival and stable reproduction, allowing them to have longer lifespans, larger body sizes, and fewer offspring. ex: humans
- their ecologies would be stable with limited resources or competitive.
Explain character displacement and how it might suggest coevolution between two competing species. Why would using character displacement to infer coevolution be problematic, and what would the alternative explanation be?
This suggests coevolution because it could suggest that each species is evolving in response to the other species.
This is problematic because it goes against the principle of competitive exclusion; an alternative explanation is that each species is adapting to different parts of the environment.
Define Batsian mimicry and describe the community relationship between the model species and its Batesian mimic species. Provide an example to illustrate your explanation.
Did the mimicry provide an immediate advantage to the mimic species?
Batesian mimicry is when a harmless species (mimic) evolves to resemble a harmful species (the model) to avoid predation. The relationship between the model and the mimic species is often not considered a mutualistic relationship (similar to parasite/host).
No, the mimic did not provide an immediate advantage because the mimicking species started with a partial resemblance to the model, so the predators still needed to be "educated" to avoid that species. This mimicry is only beneficial is the mimicking species is less frequent than the model species.