国外动物学38-.ppt

国外动物学38-
Ecology
Ecology investigates the interactions among organisms and between organisms and their environment.
ucture.
More individuals in the younger cohorts indicates a growing population.
Life History Diversity
Species that exhibit semelparity, or “big-bang” reproduction reproduce a single time and die.
Salmon
Agave
Favored in unpredictable climates.
Life History Diversity
Species that exhibit iteroparity, or repeated reproduction, produce offspring repeatedly over time.
Lizards often start reproducing during their second year and will produce eggs every year of their lives.
Favored in more predictable environments.
Population Growth
It is useful to study population growth in an idealized situation in order to understand the capacity of species for increase and the conditions that may facilitate this type of growth.
Population Growth
If immigration and emigration are ignored, a population’s growth rate equals birth rate minus death rate.
Population Growth
Zero population growth occurs when the birth rate equals the death rate.
The population growth equation can be expressed as:
dN
dt

rN
Exponential Growth
Exponential population growth is population increase under idealized conditions.
Unlimited resources.
Under these conditions, the rate of reproduction is at its maximum, called the intrinsic rate of increase (rmax).
Exponential Growth
The equation of exponential population growth is:
dN
dt

rmaxN
Exponential Growth
Exponential population growth results in a J-shaped curve.
Exponential Growth
The J-shaped curve of exponential growth is characteristic of some populations that are rebounding.
Exponential Growth
The global human population has been in exponential growth for a long time.
At what point will we surpass the carrying capacity for our planet?
Logistic Growth
Exponential growth cannot be sustained for long in any population.
Depends on unlimited resources.
In reality, the