ECOL 3500 Test 3 Pt1

predation & competition

Competition

-,-

Predation/Parasitism

+,-

Amensalism

0,-

Neutral

0,0

Commensalism

0,+

Mutualism

+,+

Consumptive effects

When predators kill prey, limits the size of prey populations

Non-consumptive effects

When prey population size is limited because of fear of predation, rather than predation itself

How do cyclic dynamics appear between predator and prey relationship?

On the graph showing pop.1 and pop. 2 vs date, we notice that the predator tends to lag behind the prey trend

What are the three treatments used to identify consumptive vs non-consumptive effects of predator exposure?

1) Predator exclusion (electric fence)

2) Predator exclusion and food supplement 

3) Control

Lotka-Volterra model

a mathematical model that describes the dynamics of predator-prey populations over time using a pair of first-order nonlinear differential equations

**Helps ecologists understand how fluctuations in one population affect the other, showing that the prey population grows exponentially but is reduced by predation, while the predator population declines but increases with each prey consumed.

Lotka-Volterra model equation

• dN/dt=rN-cNP

c = rate at which prey are captured (capture efficiency)

N = prey population size

P = number of predators

Predation rate

the frequency with which a predator captures and consumes its prey

How is predation rate determined?

by the probability of a random encounter between predator and prey (NP) and the probability that such an encounter results in prey’s capture (c)

• use predator population L-V model

What’s the equation for the prey population using Lotka-Volterra?

dN/dt = rN-cNP

• r - intrinsic growth rate of prey (b-d)

• N - number of prey

• c - capture efficiency

• P - number of predators

What’s the equation for the predator population using Lotka-Volterra?

dP/dt = acNP - mP

• a - efficiency of converting 1 prey to 1 predator offspring 

• c - capture efficiency

• N - number of prey

• P - number of predators

• m - predator mortality rate, per capita

What are the axis of density charts?

X - prey density

Y - predator density

Density chart - at what number of predators is prey abundance stable?

When rate of change (dN/dt) is zero

Prey population stable when the number of predators equals…

… the ratio of prey’s growth rate and predator’s capture efficiency

When are populations of predators stable?

Predator population is stable when production of new predators is equal to mortality of existing predators

Predator-prey cycles- x-axis?

Number of prey (N)

N = m/ac

Predator-prey cycles- y-axis?

Number of predators (P)

r/c

Prey isocline

represents the number of predators at which N is stable

• On a graph with predator population on the y-axis and prey population on the x-axis, a prey isocline shows when the prey population is stable, meaning its growth rate (\(dN/dt\)) is zero

If P < prey isocline

dN/dt is positive

If P > prey isocline

dN/dt is negative

A decrease in the prey population causes…

a decrease in the predator population

A decrease in the predator population allows…

an increase in the prey population

An increase in the prey population allows…

an increase in the predator population

An increase in the predator population causes…

a decline in the prey population

What are the assumptions of the Lotka-Volterra in nature?

It assumes that predators have a constant capture efficiency across prey population sizes - though we know this isn’t the case

functional response

describes how a consumer's rate of food intake changes with the density of its food source

Type 1 functional response

Rate of prey consumption increases LINEARLY with prey density until the predator is satisfied, at which point it abruptly plateaus

• least realistic as capture efficiency has no “slowing period”

Type 2 functional response

Rate of prey consumption slows as prey population density increases, eventually reaching a plateau

• Consumption rate decreases at high densities because of a time cost associated with handling prey item

Type 3 functional response

Rate of prey consumption initially low, increases rapidly when prey density is moderate, and slows when prey density is high

Low consumption rate at low prey densities because:

• Available prey hiding in refuges

• Predators had less practice catching prey

• Prey switching

Examples of behavioral defenses against predation

alarm calling, vigilance, reduced activity, spatial avoidance

Examples of chemical defenses against predation

compounds that are unpalatable or hard to digest

aposematism

an ecological defense strategy where animals use a conspicuous signal, such as bright colors or distinct patterns, to warn predators of their unpalatability or danger

Mullerian mimicry

multiple unpalatable species evolve similar patterns of warning coloration (honest signal)

Batesian mimicry

harmless species mimic the color patterns of species that are harmful to predators to avoid predation (dishonest signal)

Coevolution

Where two or more species evolve together in response to each other, meaning an evolutionary change in one species can cause a change in the other, and vice versa.

Are specialist herbivores or generalist herbivores more likely to have tolerance to plant defenses?

Specialists

What sets the carrying capacity and causes competition?

Limited reources

Characteristics of resources

• Can be regenerated/renewable or nonrenewable

• Can come from inside or outside the ecosystem where competitors live

What does the graph showing carry capacity look like?

x - time

y - population size

• k is carrying capacity 

• k/2 is shown as well 

Intraspecific competition

competition occurring between individuals of the same species

Interspecific competition

competition occurring between individuals of the different species

Exploitative competition

• occurs when individuals consume a resource, not leaving enough for others

• No direct interactions between individuals

• Intra or inter

Interference competition

• occurs when individuals directly alter the resource-attaining behavior of others

• Intra or inter

• Interference through aggressive interactions

Allelopathy

A type of interference through chemical interactions

Apparent competition

occurs when individuals that do not directly compete for resources affect each other indirectly via a shared predator (or parasite)

• Interspecific only

Liebig’s law of the minimum

A population increases until the supply of the most limiting resource prevents it from increasing further

Competitive asymmetry

effects of competition on two competitors are negative but are usually unequal

Competitive exclusion principle

2 species cannot coexist indefinitely when they use a limiting resource in the same way

Resource (niche) partitioning

species use a limited resource in different ways

Spatial niche partitioning

species that eat the same foods occupy different microhabitats

Dietary niche partitioning

species that occupy the same habitat eat different prey

Logistic growth with intraspecific comp. equation

dN/dt = rn(1-(N/K))

• dN/dt = instantaneous growth rate

• r = intrinsic growth rate, per individual (b-d; closed population)

• N = population size

• K = carrying capacity

Logistic growth for interspecific competition equation

dN1/dt =r1N1(1-((N1+ aN2)/K1)

• a = competition coefficient (coverts species 2 into equivalent number of species 1)

• N2 = population size of species 2

What does alpha stand for in logistic growth?

The competition coefficient

• The effect of an individual of species 2 on the rate of population growth of species 1

Competition coefficient - alpha (a) > 1

Inter > Intra

• competitive effect of species 2 on population growth of species 1 is greater than that of species 1 density dependence

Competition coefficient - alpha (a) < 1

Inter < Intra 

• Competitive effect of species 2 on the population growth of species 1 is less than that of species 1 density dependence

What does it mean if isoclines do not cross?

Either species 1 or 2 always wins, extinction of the other

What does it mean if isoclines cross

Winner depends on initial size populations

Coexistence

When interspecific competition is weaker than intraspecific competition

• populations limit themselves more heavily/before their competitors do 

Functions of mutualisms

Resource acquisition

• Water, food, nutrients, space to live

Pollination and seed dispersal

Defense against enemies

Facultative mutualism

• Species do not require the fitness benefits provided by their interaction to persist

• Species do/does better when in mutualistic partnership

Obligate mutualism

• Species require the fitness benefits provided by their interaction to persist

• Obligate mutualist cannot survive without the partner species