Population Ecology & the Distribution of Organisms

Chapter 40

scientific study of the interactions between

organisms and the environment

ecology

a group of individuals of the same species

living in an area

population

a group of populations of different species

living in an area

community

the community of organisms in an area and

the physical factors with which they interact

ecosystem

a mosaic of connected ecosystems (includes

seascapes)

landscape

the sum of all of Earth’s ecosystems and

landscapes

biosphere

organismal ecology population ecology community ecology ecosystem ecology landscape ecology global ecology

framework of ecology

how the organism meets the challenges

posed by its environment

organismal ecology

factors that affect population size and how

and why it changes through time

population ecology

how interactions between species affects

community structure and organization

community ecology

energy flow and chemical cycling

between organisms and the environment

ecosystem ecology

factors controlling exchanges of energy,

materials, and organisms across multiple ecosystems

landscape ecology

how regional exchange of energy and

materials influences the functioning and distribution of organisms across the biosphere

global ecology

long-term prevailing weather conditions in a

given area components include:

temperature precipitation sunlight wind

climate

nonliving parts of the environment that affect

the distribution and abundance of organisms

abiotic factors

living factors (other organisms) in an

individual’s environment that affect the distribution and abundance of organisms

biotic factors

major life zones

terrestrial biomes characterized by vegetation type

aquatic biomes characterized by physical environment

biomes

area where one biome grades into another may be wide or narrow

ecotone

tropical forest Savanna desert chapparal temperate grassland coniferous forest temperate broadleaf forest tundra

terrestrial biomes:

wetland estuaries lakes streams and rivers intertidal zones coral reefs oceanic pelagic zone marine benthic zone

aquatic biomes

constant rain high temperatures great biodiversity includes:

tropical rain forest (200-400 cm of rain/year) tropical dry forest ( 150-200 cm of rain/year)

tropical forest

seasonal rain (30-50 cm/year) dry season (up to 9 months) high temperatures fires common grasses, nonwoody plants large herbivores and predators

savanna

low precipitation (less than 30 cm/year) temperatures vary seasonally and daily low, scattered vegetation (many C4 and CAM

plants) many nocturnal animals

desert

seasonal precipitation (30-50 cm/year) hot, dry summers; cool, rainy winters shrubs and small trees

chapparal

seasonal precipitation (30-100 cm/year) cold, dry winters; hot, wet summers grasses and nonwoody plants large, grazing mammals; borrowing mammals

temperate grassland

30-70 cm of precipitation/year cone-bearing trees (conifers) migratory birds, brown bears, moose, Siberian

tigers, etc.

coniferous forest (taiga)

70-200 cm of precipitation/ year deciduous trees (drop leaves before winter) migratory birds, hibernating mammals

temperate broadleaf forest

20-60 cm of precipitation/ year cold winters, cool summers mosses, grasses, nonwoody plants and lichens permafrost (permanently frozen soil layer) migratory birds, musk ox, caribou, reindeer,

bears, wolves, etc.

tundra

saturated by water at least sometimes high nutrient levels cattails, sedges frogs, alligators, herons, crustaceans, etc.

wetlands

transition zone between a river and the sea high nutrient levels saltmarsh grasses oysters, crabs, fish, etc.

estuaries

light decreases with depth includes:

oligotrophic lakes nutrient-poor, oxygen-rich

eutrophic lakes nutrient-rich, oxygen-poor due to high

decomposition

lakes

headwater streams

often cold, clear and swift narrow with rocky bottom

downstream rivers generally wide and meandering; silty bottoms

streams and rivers

periodically submerged and exposed by the

tides great variations in temperature and salinity high oxygen and nutrients levels many animals attach to rocks or bury

themselves when tides go out

intertidal zones

formed from skeletons of corals much biodiversity

coral reefs

open, blue waters (70% of Earth’s surface) low nutrient levels clear water; photic zone extends deeper high oxygen content due to surface winds phytoplankton (photosynthetic bacteria) zooplankton (invertebrate larvae, krill,

protists, etc.) fishes, sea turtles, marine mammals

oceanic pelagic zone

seafloor mostly cold and dark with increased pressures deep-sea hydrothermal vents;

chemoautotrophic prokaryotes fishes, arthropods, echinoderms

marine benthic zone

pelagic zone benthic zone

Aquatic Biome Zones

includes:

photic zone upper zone sufficient light for photosynthesis

aphotic zone lower zones little light penetrates

pelagic zone

bottom of the pelagic zones may be deep or shallow

benthic zone

narrow layer of abrupt temperature change separates upper, warm layer from deeper,

cold layer

thermocline

dispersal biotic factors abiotic factors

distribution of organisms is affected

by:

movement or individuals or gametes away

from their area of origin or from areas of high population density

contributes greatly to global distribution of organisms

dispersal

negative interaction with predators or

herbivores presence of pollinators (bees, birds), food

resources, parasite and pathogens, competitors

biotic factors

temperature, water, oxygen, salinity, sunlight,

rocks, soil, etc.

abiotic factors

number of individuals per unit area or volume examples:

number of oak trees per km2 number of bacteria per mL in a culture

population density

pattern of spacing among individuals within

the boundaries of the population

dispersion

immigration

influx of new individuals from other areas emigration

movement of individuals out of a population birth rates death rates

population density is affected by:

clumped uniform random

dispersion patterns

individuals aggregate in certain areas most common pattern certain areas more favorable to survival than

others

clumped

evenly spaced dispersion may be due to territoriality (defense of a

bounded physical space)

uniform

unpredictable spacing individuals have no strong attractions or

repulsions common with wind-seeds (dandelions)

random

study of the vital statistics of populations and

how they change over time involves investigation of birth rates and death

rates

demography

age-specific summary of the survival pattern

of a population best constructed by following the fate of a

cohort* from birth to death life table determines the number of individuals

that die in each age-group and calculate the percentage of the individuals that survives to the next age-group

*cohort a group of individuals of the same age

life table

a plot of the proportion (or numbers) of a

cohort’s surviving individuals at each age

survivorship curve

Type I curve Type II curve Type III curve

types of survivorship curves

flat at the start (low death rates in early and

middle life) followed by a steep drop (as death rate increases in older age groups)

common in large mammals (including humans) that care for young

Type I curve

drops sharply at the start (due to high death

rate of the young) then levels off common in organisms that produce large

numbers of young but provide little or no care

Type III curve

Intermediate curve constant death rate over the organism’s life

span

Type II curve

age-specific summary of the reproductive

rates in a population constructed by measuring the

reproductive output of a cohort from birth until death

for a sexual species, it tallies the number of female offspring produced by each age-group

reproductive tables vary greatly by species

reproductive table

change in population size = birth + immigrants – deaths – emigrants

ΔN = B – DΔt

(ΔN = change in population size, Δt = change in time, B = # of births, D = # of deaths)

If N= population size and t = time, then:

expected # of births per year B = bN

(b = per capita birth rate, N = population size)

expected # of deaths per year D = mN

(m = per capita death rate, N = population size)

Also:

ΔN = bN - mNΔt

So:

difference between the per capita birth rate

and death rate r = b - m

per capita rate of increase (r)

when per capita birth and death rates are

equal (b = m) (r = 0)

ΔN = 0Δt

zero population growth

population increase under ideal conditions

(abundant resources) ΔN = rmaxN

Δt

(rmax = r under ideal conditions)

exponential population growth

maximum population size that a particular

environment can sustain limiting factors may include food, shelter,

water, etc.

carrying capacity (K)

density-dependent selection selection for traits that are sensitive to

population density and are favored at high densities

operates in populations near the carrying capacity (strong competition)

example: mature trees in an old growth forest

K-selection

density-independent selection selection for traits that maximize reproductive

success at low densities (uncrowded) occurs in populations well below the carrying

capacity (less competition) example:

weeds growing in an abandoned agricultural field

r-selection