10 Biology, Ms Mayfield
How do predator and prey influence each other?
The mutual influence in predator-prey- systems often follows a typical form. The statistics on showshoe hare and lynx populations in the Canadian Hudson Bay, gathered over more than 50 years by counting the sold pelts of both species, can point towards the relative population development of the predator and prey population in nature.
These graphs can be interpreted to make a statement about the mutual effect predator and prey populations have on each other.
Growth causes _______________
Prey Predator
Decline _______________
These typical fluctuations on population density appear in many predator-prey-systems and enable us to set up a ruleset (developed by LOTKA and VOLTERRA).
1. Rule: The population densities of predator and prey fluctuate _______________. The ___________ and ______________ of the _____________-density always follow those of the ____________-density (= the phases are ___________________)!
2. Rule: Over the long term the ______________ population density of predator and prey _____________________________________!
Terms: (not all have to be used!) maxima; minima; average; stays the same; linear; exponential; periodically;
predator; prey; cancel each other out; shifted; overlapping; rises; declines
10 Biology, Ms Mayfield
The first and second LOTKA-VOLTERRA-rules do not always completely apply in nature though. Two of the most important limitations are:
a) _____________________________________________________________________
_____________________________________________________________________.
b) _____________________________________________________________________
_____________________________________________________________________.
How do outside factors influence a predator-prey-system?
If humans consider an organism to be vermin we often will drastically influence their population development, for example by using insecticides. Aphids for example damage rose-growers crops, so they use a appropriate poison. The natural enemy of aphids (prey) are ladybugs (predator). The strong decline in the aphid population has a significant effect on the ladybug population with which it interacts:
Use of poison!
Density
ladybugs (predator): aphids (prey): time
Task:
Set up a hypothesis for the development of both populations after a short term use of insecticides.
3. Rule: After a strong decimation of predator and prey population densities (e.g. through ___________________________________
_______________________ etc.), the ___________ population will recuperate significantly quicker and stronger at first (reason:
____________________________________________________________
___________________________________________________________)!
