Lecture 10: Population Dynamics Flashcards
What does population dynamics refer to?
the spatial and temporal changes in the characteristics of populations
What 2 main factors cause fluctuations in population size and density?
- extrinsic/environmental changes
2. internal stability
What is internal stability?
A measure of how quickly populations can respond to environmental change
What types of species would you expect to have higher internal stability? why?
LARGE, LONGER lived organisms respond more slowly to environmental change
- lower surface area to volume ratio and are more likely to be endothermic (better able to maintain homeostasis and survive enviro fluctuations)
- longer generation times have less fluctuation in birth rate - less able to recover after large decline in population
ex. wolverines in Canada
What types of species would you expect to have lower internal stability? why? Give an example of a species
SMALL organisms with SHORT generation times respond rapidly to environmental change
- higher surface area-volume ratio so they are more vulnerable to changes in temperature
- short generation times mean they reproduce quickly and can quickly adapt to change
ex. phytoplankton in Lake Eerie
T or F: most populations in nature smoothly reach their carrying capacity. Why/why not?
FALSE.
Most overshoot K and experience die-off because their internal stability is high and therefore their response to their own density is delayed
Describe population cycle
A regular pattern of oscillation in population size
How is harvesting data used to monitor population dynamics? How can this be misleading?
The number of individuals harvested in a given time period can give a good estimate of the population size
This can be misleading because the popularity of hunting a particular species may change over time, and if there are less hunters, less individuals are being hunted and counted so the population size will appear small but this may not reflect the reality
ex. Gyrfalcons: when harvesting intensity was high, there was a clear population cycle but when it was low it looks like the population cycle doesn’t exist, even though it still would
T or F: population cycles can be synchronized across species
TRUE
ex. the 3 species of Grouse in Finland with 6-7 year pop cycles
If environmental variation is typically not regular or predictable, why do populations respond cyclically?
some experience predictable delays in response to their own density
there may be some intrinsic quality of the species that prevents birth rates from falling and death rates from rising as the pop growth approaches K
What are the 3 responses to approaching and reaching carrying capacity?
- Logistic growth (theoretical)
- Natural response
- Delayed response
Describe the expected response of a population as it approaches K if it were following the logistic growth model?
Pop growth would start small, increase rapidly, and then plateau and level off before reaching K
Describe the natural response for populations as size approaches K?
Slow start Rapid growth Slight overshoot of K Slight die off increase and smaller overshoot of K Slight die off
Fluctuation around K that gradually levels out just below K
Describe the delayed response for populations as size approaches K?
slow start rapid growth massive overshoot of K massive die off rapid increase and overshoot of K
repeatedly massively overshoots K and experiences large die offs
What 3 kinds of populations may experience delayed responses to environmental change?
- those with discrete breeding intervals
- ex. large mammals (moose, deer) - those that can store energy resources
- ex. daphnia water fleas - those that experience time delays between developmental stages with different resource requirements
- ex. blowflies
