Population Ecology

Question 1

How are populations described?

Answer 1

Number, spatial distribution, age/size distribution, dynamics-birth, death, immigration and emigration.

Question 2

What is density?

Answer 2

Number of individuals per unit area or volume-sampling.

Question 3

Dispersion

Answer 3

How individuals are spread through space.

Question 4

Clumped groups

Answer 4

Individuals grouped with space between groups-generally response to patchy distribution of resources or grouping behaviour.

Question 5

Uniform Groups

Answer 5

Individual’s spaced evenly throughout habitat. Response to even distribution of resources, spacing behaviour.

Question 6

Random Groups

Answer 6

No pattern of spacing through habitat.

Question 7

What is a cohort?

Answer 7

Group of individuals of the same age in a population.

Question 8

What does a life table track?

Answer 8

Tracks changes in a cohort through its collective lifespan. Tabulates numbers dying through each age interval, tabulates age specific chance of dying in each interval. Enables us to plot survivorship curves.

Question 9

Survivorship Curves

Answer 9

Plots survivorship as function of percentage of lifespan for a cohort.

Question 10

Type 1 Survivorship Curve

Answer 10

Most individuals survive for most of the maximum lifespan, with heavy mortality towards the end. Small amount of offspring, lots of care for each.

Question 11

Type 2 Survivorship Curve

Answer 11

Individuals face constant probability of dying through lifespan. “Field of bullets,” model.

Question 12

Type 3 Survivorship Curve

Answer 12

Young individuals face heavy mortality, after reaching a certain point in lifespan, mortality becomes much lower. Large number of young, small investment in each.

Question 13

What is the assumption in a model of population growth

Answer 13

Emigration and Immigration are equal.

Question 14

Parameters of Models of Population Growth

Answer 14

N=Number of individuals in a population. G=Number of new individuals added by reproduction. r=per capita increase (average contribution of new individuals per pre existing individuals-constant). K= max number of individuals that habitat can support (carrying capacity).

Question 15

Exponential Growth Model

Answer 15

Ideal conditions, no limiting factors, no death. G=rN. Population size is purely a function of number of individuals in a population and per capita increase. Unrealistic, but models what is seen in populations in a new environment or in recovery from rapid decrease.

Question 16

Logistic Growth Model

Answer 16

Incorporates limiting factors. G=rN((K-N)/K). K will vary according to space, time, circumstances and species. Populations will grow their fastest when population size is intermediate relative to K. As populations increase in size, factors limiting growth will have increasing effects bringing population to a halt.

Question 17

Density Dependent Factors

Answer 17

Birth rates decreasing/death rates increasing with increasing population size. Causes-intraspecific competition for limiting resource, degradation of environment quality, predation increase.

Question 18

Density Independent Factors

Answer 18

Mortality produced by factors having nothing to do with population size ex: catastrophic weather.

Question 19

Life Histories

Answer 19

Combination of reproductive characteristics and life expectancy, characterizing a species or population-produced and maintained by natural selection.

Question 20

Reproductive Characteristics

Answer 20

Number of offspring per reproductive event, age at first reproduction, length of reproductive lifespan, investment in offspring.

Question 21

Trade-offs required to fulfill reproductive characteristics

Answer 21

Time, energy and nutrients.

Question 22

r vs K selected organisms

Answer 22

r= organisms that breed in large numbers. K=organisms that breed in small numbers.

Question 23

r selected environments

Answer 23

Transient, rich resources, but unpredictable density independent controls. Strongly seasonal. Form basis of trophic pyramids in many ecosystems.

Question 24

K selected environments

Answer 24

Climax with population of organism generally near carrying capacity-hard time dealing with extreme environment changes.

Question 25

Life History Evolution

Answer 25

Conspecific guppy populations in Trinidad coexist with either Kilifish or Pike-Cichlids. Growth strategy shifts for guppies depending on which fish they live with. (Kilifish eat small immature guppies-guppies grow quick and mature at larger size vs Pike-Cichlids eat larger, mature guppies, so guppies mature at a smaller size).

Question 26

Management of wild stocks

Answer 26

Estimate maximum sustained yield, which is the maximum harvest which can be taken periodically from a wild population without causing it to decline.