Ecology Chapter 8

Exploitation

Interaction in which one species increase in fitness by consuming all or part of another species, which then have a decrease in fitness. 

Predation

Predator kills and consumes prey. 

Parasitism

Parasite obtain energy from their host usually without killing them

Herbivory

Consume plants typically not killing them.

Terminological issues

A shared resource is also someone’s prey which was also someones mother.

Resources aren’t just finite______.

They can be abiotic and unlimited like space, water, etc.

In simple systems, predators ____, then the _____.

But nature is rarely simple. By adding refuges or allowing immigration, ____.

Eat until prey crashes, then the predator crashes too. 

Prey can persist and sometimes win. 

The Hudson Bay records:

Explain predator-prey oscillation from fur collection data from the late 1700s through about 1950.

Multiple theories have been proposed throughout the years…

• ___

• ___

• ___

• ___

• ___

Sunspot radiation

Disease and overpopulation

Physiological stress at high densities

Starvation of hares

Predation

After many decades of research, we can conclude that the population cycle in snowshoe hares is the result of ____.

An interaction among three trophic levels: the hares, their food supply, and their predators. 

Does Alfred Lotka and Vito Volterra equation work for prey and predator hosts?

Yes. 

What is the Prey Equation?

(Change in prey population density) = (Exponential population growth in prey) - (Number of prey lost to exploiters)

How fast prey can change their population is dependent on what?

How fast they can grow (r_max) minus how many of them get eaten. 

What does the variable “f” stand for in the 2nd prey equation?

Rate of (capture) foraging. dN_p/dt = rN_p - fN_p*N_e

What is the Exploiter Equation?

(Change in prey population density) = (Births possible from prey consumption) - (Natural deaths of exploiters)

How fast predators can change their population is dependent on what?

How fast they can grow (r_max) from eating the prey, munus how many of them just DIE.

If the number lost to predators leads to more predators living, we should have an ____ which gets multiplied in the 2nd equation ___.

Exploiter Conversion Factor (c). 

dN_e/dt = rN_p - cfN_p*N_e - dN_e

What does the variable “c” stand for in the 2nd exploiter equation?

Exploiter conversion factor.

In the equilibrium conditions graphs of exploiter-prey, what are the x and y-axis?

x-axis represents prey population density (N_p).

y-axis represents exploiter population density (N_e).

Lets say the horizontal line is a prey zero-growth isocline, and at a constant density of exploiters (lets say 5 at y-axis) and doesn’t specify a specific prey density.

What happens to prey population below and above the isocline?

What about if the isocline line was at the x-axis, how does that affect exploiters?

If theres 5 or less predator in a population, then theres an increase in prey population density, while if there are more than 5 predators, the prey population density decreases.

If theres 5 or less prey, then the exploiter population will decrease due to lack of resources. while if there are more than 5 prey, the exploiter population will increase as there is ample food supply.

What are the variables in N_e = r/f ?

The change in number of exploiters is equal to the rate of growth of prey (r) divided by the exploiter capture rate.

What are the variables in N_p = d/cf ?

The change in number of prey is equal to the per capita death rate divided by the (conversion rate times hr capture rate).

What does neutral stability result in? What does larger disturbances result in?

Exploiter-prey cycles of constant amplitude.

It moves the densities further from the equilibrium point and leads to larger circles. 

The bigger the amplitude oscillation, the _____.

Bigger the chance of extinction. 

In the equilibrium conditions graphs, with very large amplitude cycles, the prey may ___, in which case the exploiter density ____.

May go extinct first (incomplete gray circle) in which case the exploiter density decreases until exploiters also go extinct..

Functional response (graph)

The number of prey eaten per exploiter per unit of time.

Functional response (graph):

Type 1

What L/V predicts but is unrealistic (they can’t eat unlimited amounts, predators will satiate).

Functional response (graph):

Type 2

Shows that consumption has to level off at some point, tummies are full.

Functional response (graph):

Type 3

Most realistic, as lower prey density makes a food item more work than it is worth. 

Functional response (graph):

Type 3 example

Berries just starting to ripen. There is a few, but not enough to make it worthwhile.

What is L/V? X

A ratio used in ecology to describe the relationship between the density of prey (L) and the density of predators (V), predicting the rate of prey consumption.

Allee Effects

A phenomenon in ecology where a population's growth rate decreases as the population density becomes lower. This can result in difficulty finding mates and reduced survival rates.

Organisms that do not congregate tend to suffer reduced fitness as density is reduced. 

Sometimes high densities can ____. But sometimes, they ___.

Protect from predators. But sometimes they draw a little too much attention. 

Compare allee effects on populations of flowers and pollinators.

When the population density of flowers is low or isolated, pollinators may struggle to find sufficient mates and food sources, leading to decreased reproduction rates. Conversely, higher densities of flowers can attract more pollinators, enhancing reproduction and survival of both species.

Crypsis

Form of camouflage that allows an organism to avoid detection by predators or prey. This can involve coloration, patterning, or behavioral adaptations that blend with the environment.

Object mimicry 

Organism looks like an inanimate object.

Ex) Stick, leaf, or stone. 

Countershading X

Dark on top and light on bottom. Helps reduce shadows and make the body shape less visible.

Ex) Sharks, penguins

Disruptive coloration X

Patterns (spots, stripes) break up the outline of body, making it harder to identify or focus on. 

Ex) Zebra stripes

Masquerade X

Organism is recognized as something else that’s not edible or of interest.

Ex) Caterpillars that look like bird poop or twigs. 

Müllerian mimicry

Two or more harmful species evolve similar warning colors, reinforcing predator avoidance.

Batesian mimicry

A harmless species mimics the a harmful or toxic one to avoid predators. 

Primary defense 

Mechanisms that organisms use to avoid detection, predation, or harm. Including physical, chemical, or behavioral adaptations. This prevents an attack BEFORE it happens. 

Secondary defense 

Mechanisms that organisms use to evade or minimize harm AFTER detection, such as fleeing, hiding, or displaying defensive behaviors.

Tertiary defense

Mechanisms that organisms use to recover or heal from injury or harm AFTER AN ATTACK, often involving physiological responses or repair processes.

Arm Race

Political term for weapons having to be able to beat another military.

Evolutionary Arms Race. When it’s used.

As quickly as prey develop a protection to save themselves, exploiters have found a way to defeat that protection. Used when tertiary defense doesn’t work. 

Red Queen Hypothesis

A theory suggesting that species must continuously adapt and evolve in order to not go extinct. 

Ecological anachronisms

Species or traits that are out of sync with their current ecosystem due to changes over time, often resulting from the extinction of their natural partners or predators.