Ecology
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Transcript of Ecology
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
Radio tracking
Traps
What changes a Population’s Size?
• Changes to population size– adding &
removing individuals from a population
• birth• death• immigration• emigration
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?