Bio 171 Lecture 4: Population Ecology II

Carrying capacity (K):

Max # of individuals a habitat can sustain indefinitely w/o environmental deterioration. Pop grows beyond K when d+e>b+i. [(K-N)/K]

Density-independent factor:

Describes factors severe natural disasters that influence N w/o regard for population density (food availability. etc).

Density-dependent factor:

Describes processes affecting pops. influenced by the # individual organisms, (resources usage, predation susceptibility, parasitism).

Equilibrium

NEED

Limiting factors:

Any biotic/abiotic factor that restricts existence, #, reproduction, or distribution of organisms. (biotic factors can regulate, abiotic can’t).

Logistic growth:

Pop. limited to carrying capacity of habitat, exponential growth is stopped. DN/dt=rmax*Nt* [(K-N)/K]

overshoot

When pop. grows exponentially so fast that it exceeds K before stabilizing.

Population density:

N/geographic range. Provides info on how crowded/dispersed pop. is. Can be misleading when pop. is distributed randomly and location of one individual has no influence on next individual’s location. Uniform (evenly distributed) pops. depend on same set of limited resources.

Apply the logistic growth equations to predict population growth rate and population size in the future. (Note: we will give you equations on the exam, but you will have to recognize which is which and know how to apply them.)

Has K.

Explain why population growth rate is constant under exponential growth, but that population growth rate slows as population size increases under logistic growth.

Exponential: no resource limitation hindering pop.growth. Logistic: Due to crowding/competition for resources.

Explain why populations do not grow exponentially forever.

Large pop. w/ intraspecific competition/density-dependent biotic factors creates a scarcity of resources regulating pop to K.

Identify exponential vs. logistic growth curves.

Exponential: Upward curve. Logistic: S-curve.

Explain the factors that influence the per capita growth rate (r) of populations undergoing logistic growth.

Biotic factors that have negative feedback are the only factors that can regulate r. Logistic must be density dependent and the r must change.

Predict the expected graphical patterns if A) a density-dependent factor is influencing the population growth or B) no density-dependent factor is influencing the population growth.

A. Logistical graph (s curve). B. exponential graph (upward curve).

Define population regulation and summarize the factors that regulate population growth.

Regulation to oscilate pop. around an equalibrium value. biotic with negative feedback can regulate population growth

As population size increases in an already large population, what changes do you expect to see in birth rate and death rate?

Decrease in b (less resources), increase in d (more predation) leading r to decrease.

What sets carrying capacity?

Resources such as intrasepcific competition.

How does intraspecific competition relate to carrying capacity?

Only intraspecific competition can regulate K.

How does r change over time in a population as it grows from a very small population relative to carrying capacity to a large population near (and eventually at) carrying capacity?

Small: competition for resources doesn’t limit r so it increases. Large: individuals more vulnerable to density-dependent factors so r gets smaller and flattens out on a curve.

When a population is growing logistically, what does the pattern look like if time is on the x-axis and density is on the y-axis? What does the pattern look like if density is on the x-axis and r is on the y-axis? What specific factor causes the pattern shown in both of these

graphs?

1. S-shape. 2. Linear diagonal line; as n increases in density, r decreases due to resource limitation.

What equation can be used to describe logistic growth?

dN/dt=(rmax)*Nt*[(K-N)/K].

How does the equation to describe logistic growth differ from the one for exponential growth?

Considers K while exponential doesn’t.

What happens to the term in parentheses in the logistic growth equation as a population moves from a very low density to a density very close to carrying capacity?

Term moves further from exponential growth and gets closer to dN/dt=0 (stable pop.).

In a population experiencing logistic growth, how does dN/dt change over time as you move from a very low density to a density very close to carrying capacity?

Term moves further from exponential growth and gets closer to 0 (stable pop.).

At which point (relative to density) are exponential and logistic growth most similar?

Low density b/c density dependent limiting factors aren’t truly impacting anything yet.

Does rmax change over time in logistic growth? If so, how? Does 'real' r change over time in logistic growth? If so, how?

NEED.

What happens if the population size exceeds carrying capacity? What happens to dN/dt when N > K? What happens to population size when N > K?

DN/dt: <0 (pop. shrinks).

What factors can regulate population size?

DN/dt: <0 (pop. shrinks).

What factors can influence (but not regulate) population size?

Abiotic factors (temp., pollution, salinity, pH).

In ecology terminology, is there a difference between “influence” and “regulate”?

Influence: Change that doesn’t attract pop. to equilibrium. Regulate: pop. oscillates around a stable equilibrium.

How is population regulation like a thermostat?

It adjusts and requires negative feedback.

How can you tell if a figure/graph shows density dependence or density independence?

Diagonal line (density v r): Density dependence showing logistic growth. Horizontal line: Density independence showing exponential growth.