PACKET #80CHAPTER #52

Population Ecology

Introduction & Review

Population Group consisting of

members of the same species that live together in a prescribed area at the same time.

Population Ecology The study of numbers of

individuals of a particular species, at a given time and location, and the interactions of that population with other populations and the environment

Population dynamics Study of changes in

populations

IMPORTANT FEATURES OF POPULATIONS

Population Ecology

Population Density

Population Density This is how population size is expressed The number of individuals of a species per unit space

Dispersion

Dispersion Describes the spacing

of individuals and there are three types.

Types of Dispersion

Uniform Dispersion Individuals are evenly distributed

Clumped (Aggregated) Dispersion Most common type Individuals are concentrated in specific parts of the habitat

Patchiness Occurs as a result of distribution of resources or by

asexual reproductionRandom dispersion

Occurs when individuals of a population are spaced throughout an area in a manner that is unrelated to the presence of others

Least common; hardest to observe Results from a lack of interaction between individuals or a

homogenous environment

MATHEMATICAL MODELS

Population Ecology

Equation

∆N/∆t = b – d ∆N is the change in numbers in the population ∆t is the change in time b is the natality (birth) rate d is the mortality rate

r = b – d r is the growth rate of the population

If r is 0, the population is stable If r > 1, the population is increasing in size If r < 1, the population is declining

These equations can be expressed as dN/dt = rN N is the population size Represents arithmetic growth

Population increases by the same amount over each interval of time

TYPES OF GROWTH RATES

Population Ecology

Exponential Growth

Exponential Growth Population growth is at a

rapid pace Reflects the maximum

intrinsic rate of growth Maximum rate of growth

under ideal conditions for that population

dN/dt = rmaxN rmax represents the

maximum growth rate This type of growth may

exist for a period of time until limiting factors become important Humans have exhibited

this growth pattern for centuries—but can it last?

Exponential Growth & The Human Population I

Thomas Malthus recognized that the human population cannot continue in exponential growth There has been a large

decrease in death rate and the population continues to increase to unknown proportions No one knows the

carrying capacity of humans.

Exponential Growth & The Human Population II

Not all countries have the same growth rate Higher in developing

countries India South Asia Africa

Age structure of a country can be used to predict future population growth Shows the percentages of

population at different ages

A broader base to the age structure indicates a growing population while a narrower base indicates a stable or shrinking population.

Logistic Growth

Logistic Growth Exponential growth with

environmental resistance (carry capacity of the environment = K) incorporated into the equation

dN/dt = rmaxN((K – N) /K) N = population size K = carrying capacity

Maximum number of organisms that the environment can sustain indefinitely.

Exhibited by most natural populations.

Potential Examination QuestionLogistic Growth

Populations do not always approach and stabilize at K, but may overshoot K, followed by a population crash. Why does this occur? Provide an example. What reproductive strategies would be advantageous

at high population densities (At or close to K)? What reproductive strategies would be advantageous

at low population densities?

FACTORS INFLUENCING POPULATION SIZE

Population Ecology

Dispersal

Dispersal Movement of individuals among populations Immigration

Migration of individuals into the population Emigration

Migration of individuals out of the population If incorporated into the growth rate mathematical

equation r = (b – d) + (i – e)

Density Dependent Factors

Regulate population size and is difficult to access in nature and are limiting factors that increase in intensity as population size increases

Density Dependent Factors II

PredationDisease

Increases when contact with toxic waste, produced by population itself, increases with population size.

Competition Intraspecific

Competition between members of the same species Interspecific

Competition between members of different species

Density Independent Factors

Limit population size and are factors that do not increase in intensity as the population size increases.

Most density-independent factors have some relationship to population density.

Many climatic factors are density-independent.

Density Independent Factors

Climatic factors Sunlight Rainfall Temperature

All have impacts no matter what the population size Climatic and seasonal factors, monsoon season for

example, can severely decrease populations

LIFE “HISTORY” TRAITS OF POPULATIONS

Population Ecology

Introduction

Life history traits, products of natural selection, are traits that affect an organism’s schedule of reproduction and survival. Birth Reproduction Death

Semelparous vs. Iteroparous Species

Semelparous Species Expend their energy in

a single, immense reproductive effort Pacific salmon Agave

Iteroparous Species Exhibit repeated

reproductive cycles Most vertebrates Most shrubs Most trees

r Strategists

r strategists Have traits that

contribute to a high population growth rate. High r Small size Large numbers of

offspring May live in

unpredictable habitats Weeds Pests

• Roaches

K Strategists

K strategists Maximize the chance of

surviving in an environment where the number of individuals (N) is near the carrying capacity (K) of the environment. Population size near K Larger body size Long life span Late reproduction and

slow development Have fewer offspring May care for their young

African elephants Humans

Survivorship

Survivorship is related to r and k selection Type I Survivorship

Typical of K-selected organisms High mortality rate later in life

Type II Survivorship Characterized by constant mortality rate over time

Birds and lizards Type III Survivorship

r selected organisms. Characterized by high mortality rate early in life

Survivorship Curves

Review

Review

Students are encouraged to place their own questions and charts on following slides.