Ecology

Population Dynamics

Why do we want to measure population sizes?

• To better manage populations– To better use resources

• increase population size– endangered species (So they don’t go extinct)

• decrease population size– pests

• maintain population size– fisheries management

» maintain & maximize sustained yield

How do we measure plant and animal populations?

• Tagging (mark-recapture)– Netting– Electroshocking– Radio collars– Traps

• Animal counts (ex: deer yards)

• Counting plants – estimate over large areas

Fyke netting in spring

Tagging

Electroshocking

Electroshocking

Electroshocking

• Stream electroshocking

Radio tracking

Netting animals

Traps

What changes a Population’s Size?

• Changes to population size– adding &

removing individuals from a population

• birth• death• immigration• emigration

Natural populations of organisms

• Natural populations do NOT show linear growth!

Natural populations demonstrate exponential growth

African elephantprotected from hunting

Whooping cranecoming back from near extinction

Exponential growth rate• Characteristic of populations without

limiting factors – introduced to a new environment or rebounding from a

catastrophe

Limits to population growth

• Limiting factors – – any environmental factor that limits an

organism’s ability to survive in its environment – Examples????

• Predators

Regulation of population size

swarming locusts

marking territory= competition

competition for nesting sites

• Limiting factors– density dependent

• Biotic factors– competition: food, mates, nesting

sites– predators, parasites, pathogens

– density independent• abiotic factors

– sunlight (energy)– temperature– rainfall

Carrying capacity

• The number of organisms of one species that an environment can support over an extended period of time.

500

400

300

200

100

0200 10 30 5040 60

Time (days)

Nu

mb

er o

f cl

ado

cera

ns

(per

20

0 m

l)

• Maximum population size that environment can support with no degradation of habitat– varies with

changes in resources

Time (years)1915 1925 1935 1945

10

8

6

4

2

0

Nu

mb

er o

f b

ree

din

g m

ale

fu

r se

als

(th

ou

san

ds)

Carrying capacity

What’s going on with the plankton?

Changes in Carrying Capacity• Population cycles

– predator – prey interactions

At what population level is the

carrying capacity?

KK

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