POPULATION ECOLOGYChapter 19

ECOLOGY

Study of interactions of organisms with each other and the physical environment

Can be divided into increasingly comprehensive levels: Organismal ecology Population ecology Community ecology Ecosystem ecology

ORGANISMAL ECOLOGY

Concerned with evolutionary adaptations

Enable individual organisms to meet the challenges posed by their abiotic environments

POPULATION ECOLOGY

Concentrates mainly on factors that affect population density and growth

COMMUNITY ECOLOGY

Focuses on how interactions between species affect community structure and organization

ECOSYSTEM ECOLOGY

All abiotic factors in addition to the community of species in a certain area

Focuses on energy flow and the cycling of chemicals among the various

abiotic and biotic factors

WHAT IS POPULATION ECOLOGY?

Study of how members of a population interact with their environment

Focuses on factors that influence a population’s: Size Growth rate Density Structure

POPULATIONS

Distribution Pattern of dispersal of individuals across an

area Affected by availability of resources

nonliving (abiotic) and living (biotic) components of an environment that support living organisms

Limiting factors Environmental aspects that particularly determine

where an organism lives

Range Portion of the globe where the species can be found

POPULATIONS

Density Number of individuals per

unit area How do we measure population

density? impossible to count all individuals

in a population estimated by indirect indicators

number of bird nests

INFLUENCES ON POPULATION

Carrying capacity Number of individuals of

a species that a particular environment can support

PATTERNS OF DISPERSION….

way individuals are spaced within the population’s geographic range

Three main models of dispersion: Clumped Uniform Random

PATTERNS OF DISPERSION

Clumped pattern of dispersion Individuals aggregate

in patches

PATTERNS OF DISPERSION

Uniform pattern of dispersion Results from

interactions among the individuals of a population

PATTERNS OF DISPERSION

Random pattern of dispersion Individuals are

spaced in a patternless, unpredictable way

COMPARISON OF SPECIES

Survivorship Life history traits

1. SURVIVORSHIP

Chance an individual in a population survives to various ages

Represented graphically in a survivorship curve Plot of individuals surviving at each age in

maximum life span Uses a percentage scale Can compare species with various life spans on

same graph

SURVIVORSHIP

Type I survivorship curve Most individuals survive

until old age

Type II survivorship curve Decreases consistently

over time

Type III survivorship curve Most individuals die

early

2. LIFE HISTORY

Set of traits that affect the organisms: Reproduction Survival

Key feature of a populations pattern of survivorship

Key life history traits are: Age at first reproduction Frequency of reproduction Number of offspring Amount of parental care provided

TYPES OF LIFE HISTORIES

Organisms with an opportunistic life history: Take immediate advantage of

favorable conditions Typically exhibit a Type III

survivorship curve Organisms with an equilibrial

life history: Reach sexual maturity slowly Produce few, well cared for

offspring typically large-bodied and

longer lived Typically exhibit a Type I

survivorship curve occur in environments where

population size is at or near carrying capacity

POPULATION GROWTH MODELS

Populations fluctuate Mathematical models to

illustrate changes: Exponential population

growth Logistic population

growth

POPULATION GROWTH MODELS

1. J-shaped Curve – Exponential Growth Lag phase: Growth is small

because the population is small Exponential growth phase:

Growth is accelerating, and the population is exhibiting its biotic potential

2. S-shaped Curve – Logistic Growth Lag phase: Growth is small because

the population is small

Exponential growth phase: Growth is accelerating, and the population is exhibiting its biotic potential

Deceleration phase: The rate of population growth slows down

Stable equilibrium phase: Little if any growth takes place because births and deaths are about equal.

POPULATION GROWTH MODELS

REGULATION OF POPULATION GROWTH

1. density-dependent factor Intraspecific competition population-limiting factor effects intensify as the

population increases in density Percentage of population

affected does increase as density of population increases

Includes: Accumulation of toxic

wastes Limited food supply Limited territory

Competition and predation

REGULATION OF POPULATION GROWTH 2. Density-independent

factors population-limiting factors intensity is unrelated to

population density Population of individuals killed

remains same regardless of population size

Includes abiotic factors such as: Fires Floods Storms

HUMAN POPULATION GROWTH

Growing almost exponentially for centuries

Based on the same parameters that affect other populations Birth rates Death rates

HUMAN POPULATION GROWTH

Approximately 225,000 people are added to the world’s population every day

Approximately 82 million people are added to the world’s population every year

Current doubling time is 56 years(length of time it takes for population size

to double) More Developed Countries (MDC’s)

versus Less Developed Countries (LDC’s)

ESTIMATES OF POPULATION

Age structure of a population Proportion of

individuals in different age groups

Can help predict the future growth of populations in different countries

EFFECTS ON POPULATIONS - INVASIVE SPECIES

Non-native species that has spread far beyond the original point of introduction

Causes environmental or economic damage by colonizing and dominating suitable habitats

In United States, invasive species cost about $137 billion a year

Invasive species typically exhibit an opportunistic life history pattern

INVASIVE SPECIES

Kudzu 1876 invasive Asian vine Covers about 12,000

square miles of the southeastern United States

Has a range limited by cold winters

Grows 60 feet per season!

INVASIVE SPECIES

Biological control intentional release

of a natural enemy to attack a pest population

used to manage an invasive species

Does NOT always work!!!