External Influences on Populations

1
External Influences on Populations

• Class 9
• Presentation 2

2
Changes in populations

• Populations undergo change due to natural causes
  and human induced change
• We try and limit the effects of human induced
  chance
• Have some good examples in the local area forest
  practices and fresh water fish management on L
  Nipissing

3
Review

• In previous weeks we learned that populations are
  affected by internal factors
• Demographic events (collective mortality and
  fecundity, sex ratio, age classes, etc)
• Genetic factors such as genetic drift, out
  breeding depression, etc)

4
External factors

• Populations are also affected by external
  factors
• Habitat change
• Direct human activity
• Indirect human activity (pollution concentration
  through the food chain)
• Other organisms
• Environmental factors

5
Endangered Species Game

• The game will allow you to see how these external
  factors combine to affect populations of
  endangered species

6
Habitat Change

• Can occur through natural events, e.g. succession
  (change in vegetation through time)
• Primary succession
• Witness change in plant communities in Ontario
  over the past 18,000 yrs
• As glaciers melted, tundra vegetation became
  common, followed by open tree forests and finally
  closed forests.

7
What we know

• Glaciers covered all of Ontario
• Started to recede 18,000 years ago
• Pollen records reconstruct extent and abundance
  of tree species

McGhee, 1989
8
History of white pine

• 10,000 - 4,000 years ago
• expanded range westward and northward as glaciers
  melted

From Jacobson, G.L. 1992
9
History of white pine

• 10,000 - 4,000 years ago
• maximum abundance reached 4,000 years ago

From Jacobson, G.L. 1992
10
History of white pine

• 4,000 - 500 years ago
• cooling climate, decline in distribution of white
  pine

From Jacobson, G.L. 1992
11
Habitat Change

• Has also occurred due to direct and indirect
  influence of people
• Habitat destruction eradication of habitat, e.g.
  land clearing for agriculture
• Some estimate habitat destruction responsible
  for loss of 100 spp/day
• Habitat change less catastrophic

12
Other organisms

• Natural predators, diseases and pests
• Introduced organisms
• E.g. black rat followed people to islands and
  have caused extinction of many bird spp.
• Bio control introductions that went wrong e.g.
  when giant African snail introduced to French
  Polynesia as food source, became serious pest.
  Predatory snail, Eulandina rosea introduced. E.
  rosea became a predator to 7 endemic snail spp
  driving them to extinction in wild.

13
Direct human influences

• Commercial use whales, fish spp and populations
• In the past Hunting, trapping, poisoning
• Today recreational activity (disrupt breeding),
  Illegal hunting etc.
• Non commercial spp e.g. dolphins, sea birds as
  accidental catch

14
Indirect human influences

• Contaminants and bio-magnification through the
  food chain e.g. persistent pesticides and raptor
  populations world wide.

15
Environmental stocasticity

• Natural chance influences through weather events
• Human influenced through climate change
• Ectothermic organisms (plants, invertebrates,
  cold-blooded vertebrates have limited ability
  to respond to extreme temps.
• Endothermic influenced through food supply

16
Endangered Species Game

• Uses different external factors to illustrate how
  they may influence a given endangered species
  population.
• You will have to hand in an assignment after the
  game.