Population Ecology

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They are affected by many factors, such as competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors.

In crowded populations, increasing population density intensifies competition for resources and results in a lower birth rate.

Slide 30

Decreased reproduction at high population densities

Population size

100

80

60

40

20

0

200

400

500

600

300

Percentage of juveniles producing lambs

Slide 31

Territoriality

In many vertebrates and some invertebrates, competition for territory may limit density.

Cheetahs are highly territorial, using chemical communication to warn other cheetahs of their boundaries.

Slide 32

Territoriality

(a) Cheetah marking its territory

(b) Gannets

Slide 33

Disease, Predation, & Toxic Wastes

Population density can influence the health and survival of organisms. In dense populations, pathogens can spread more rapidly.

As a prey population builds up, predators may feed preferentially on that species.

Accumulation of toxic wastes can contribute to density-dependent regulation of population size.

For some populations, intrinsic (physiological) factors appear to regulate population size.

Slide 34

Population Dynamics

The study of population dynamics focuses on the complex interactions between biotic and abiotic factors that cause variation in population size.

Long-term population studies have challenged the hypothesis that populations of large mammals are relatively stable over time.

Weather can affect population size over time.

Slide 35

Changes in predation pressure can drive population fluctuations

Wolves

Moose

2,500

2,000

1,500

1,000

500

Number of moose

0

Number of wolves

50

40

30

20

10

0

1955

1965

1975

1985

1995

2005

Year

Slide 36

Population Cycles: Scientific Inquiry

Some populations undergo regular boom-and-bust cycles.

Lynx populations follow the 10 year boom-and-bust cycle of hare populations.

Three hypotheses have been proposed to explain the hare’s 10-year interval.

Slide 37

Snowshoe hare

Lynx

Number of lynx