Chapter 30 Population Ecology

Population ecology

the study of how and why populations change over time

What population characteristics are measured

population density and size, geographic range which is determined by the boundaries of distribution, habitat (specific environment) population dispersion is the distribution of individuals in space, age structure (relevant number of individuals of dif ages), generation time is the average time between birth and birth of its offspring, sex ratio, reproducing individuals in a population.

3 kinds of mark and recapture

hair-snares (put cat nip on a round brush, animals rub on it, their hair is snared), remote cameras, scat surveys

3 patterns of spatial dispersion

Clumped, random (pretty rare), uniform

Demography

statistical study of processes that change a population size and density through time

population growth factors

Birth and imigration

population decline factors

death and emigration

Life tables

Summarize the demographic of a population. Age-specific mortality, Age-specific survivorship, Age-specific fecundity

cohort

group of individuals of similar age

What do organisms use their energy budget for?

Growth, Maintenance, and reproduction. one function is invested in there is less energy for other functions. adjusted to maximize living offspring

Type 1 curve

high survivorship until late in life

Trade-off between fecundity versus parental care How often to breed: once or repeatedly? Age at first reproduction: when to start reproducing

type 2 curve

constant mortality rate at all ages

type 3 curve

high juvenile mortality rate followed by low mortality after critical age

Exponential model

unlimited growth

Logistic models

limited recourse and carrying capacity. Includes effects of resource limitations (intraspecific competition). Carrying capacity (K): Maximum population size that environment can sustain. Per capita population growth rate (r) decreases as N approaches K

what is this -> dN/dt = rmaxN(K − N)/K

Logistics model equation

Population regulation

Density dependent and independent factors. sometimes population density effects mortality

Density independent factors

reduce population growth regardless of populations size (abiotic environmental factors)

Density dependent factors

Crowding decreases individual growth rates, adult size, and survivorship. Also decreases fecundinty (fertility).

Other density population factors (5)

Competition within populations or between species, Sometimes increases in migratory responses, Predator-prey interactions, Parasites, Infectious diseases can cause density-dependent population regulation

Cyclic fluctuations

periodic changes in the frequency of diseases and health conditions over time. some animal populations experience cyclic fluctuations in population size.

Intrinsic Control

Hormonal and behavioral changes

Extrinsic Control

Relationship between a cycling species and other factors (food or predators)

potential drivers of the hare cycle

Weathe/Climate, Forest Succession, Food Availability and Quality (abundance, plant secondary compounds), Predation (direct and hormones)

Human population growth

Past 200 years: Humans overcame usual density-dependent population regulation; populations now grow exponentially, Expanded into most terrestrial habitats, Increased carrying capacity, Reduced death rates with improved medical care and sanitation

how long did it take the human population to reach 1 billion? 2 billion? 5 billion?

Took 2.5 million years for human population to reach 1 billion 80 years to reach second billion 12 years to jump from 5 billion to 6 billion