back to Wildlife Ecology and Management

elective course

3. Populations

Introduction of new species:
No time to change: extinction
Examples:
American grey squirrel introduced into Britain: Sciurus carolinensis has replaced the native red squirrel Sciurus vulgaris
European starling brought to New York City (starling pic), (more)
(In 1890 approximately 100 birds were released in New York City. In 1994, there was an estimated population of 140 million birds.)

Exponential growth

no limit to growth:

R-selected species

periodic limitations: Boom and crash cycles
Water flee (Daphnia magna) is adapted to exploit new environment:
high growth rate, resistent eggs produced before crash.

K-selected species

Reindeer introduced to Pribilov island. Initial exponential growth, crash, complete extinction.

It is not clear, what factors stabilize population size. Seems, that predation is more important, than previously thought. (Top-down control)

Example: predators were removed from Kaibab plateau. Mule deer population size increased from 4,000 to hundred thousand, then dropped and stabilzed at 10,000.

more on Kaibab population

The familiar 10-11 year hare-lynx cycle might not be true.

Biased data.

more

Factors affecting population size. Dependent or independent of density?:

birth and death
Disease, parasites?
Food, condition?
Nestsites, cover, fertility?
Fload?
Immigration, emigratrion

Control of population

A) raise density (protected species, overexploited game) - conservation
B) maintain density (optimal density, maximal harvest) - sustained yield
C) reduce density (harm to other species, wildlife damage) - control

Game and protected species:
different methods but same principle

Steps

Estimate present density
Evaluate limitating factors Food? Water? Disturbance? Predators?
Remove limitatons
Monitor population
Estimate carrying capacity (optimal density)

Sustained yield (game populations)

Fertility is highest, natural mortality is lowest at 1/2 of K.

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In the news: Elephant hair reveals competition BBC
"When the rainy season comes you get this big sprouting of grasses, but they can't access it until it is 30 to 50 centimetres high," Professor Cerling said. "It's got to grow tall enough before they can actually yank it off with their trunks.

"We have this one incident where they apparently missed an entire good season of grass resource; the GPS data shows that they were outside [Samburu National Reserve] in a community area where it appears that they had to compete with cattle.