Population Ecology Ecology: study of the interactions of organisms with each other & with the physical environment Population: all organisms of same species that live in a particular area Community: all of the different populations in a given area Ecosystem: all of the different populations in a given area including living (biotic) & nonliving (abiotic) parts Biosphere: portion of Earth’s surface where life exists

Patterns of Population Growth Each population has particular patterns of growth Population size can stay the same, increase or decrease according to per capita rate of increase (growth rate) Biotic potential: Highest possible per capita rate of increase for a population

Patterns of Population Growth Factors affecting biotic potential: Average number of offspring per reproduction Chances of survival until age of reproduction Age at first reproduction How often each individual reproduces Population growth patterns can be exponential or logistic

Patterns of Population Growth Exponential patterns of population growth result in a J-shaped curve because growth rate is increasing Logistic growth patterns result in an S-shaped curve because environmental resistance

Patterns of Population Growth Environmental resistance: all those environmental conditions that prevent populations from achieving their biotic potential Limited food supply Accumulation of waste products Increased competition Predation Carrying capacity: number of individuals of a species that a particular environment can support

Survivorship Curves Type I curve: individuals survive past midpoint & death comes near end of maximum life span Type II curve: survivorship decreases at a constant rate throughout life span Type III curve: most individuals die young

Human Population Growth Growth in less developed countries is in exponential growth phase Ex. Latin America, Africa, Asia Population growth is expanding rapidly Majority of people live in poverty Growth in more developed countries has leveled off Ex. North America, Europe Population growth is low Good standard of living

Human Population Growth Suggestions to reduce population growth explosion in LDC (less developed countries): Establish or strengthen family planning practices (birth control) Reduce desire for large families Provide education Raise status of women Reduce child mortality Improve economic stability Delay onset of childbearing

Age Distributions Age-structure diagrams divide the population into three groups: Preproductive Reproductive Postreproductive LDC population continues to grow as long as there are more young women enter reproductive years than older women leaving them (unstable age structure).

Regulation of Population Growth Factors that regulate population growth consist of two types of life history patterns: Opportunistic patterns Small individuals Many offspring Mature early Short life span Little or no care of offspring Ex. Insects, weeds Equilibrium patterns Large individuals Large populations Slow to mature A lot of care of offspring Long lifespan Ex. Birds, mammals

Regulation of Population Growth Cont. Density-independent factors Abiotic factors (weather, natural disasters) Effects population all the same Opportunistic life history pattern Density dependent factors Biotic factors (competition, predation, parasitism) Effects depend on size of population The more dense a population, the faster a disease might spread Equilibrium life history pattern

Competition Occurs when members of a different species try to utilize a resource that is in limited supply Light, space, nutrients Ecological niche: role organism plays in the community that includes its habitat & interactions with others Habitat: where an organism lives Competition exclusion principle: no two organisms can occupy the same niche at the same time when resources are limited Resource partitioning reduces competition by dividing the feeding niches.

Predation Predation occurs when one organism feeds on another (prey) Predator-prey cycling can occur if: The predator population overkills the prey & forces a decline in predators. The prey population has huge booms of population growth beyond their carrying capacity which results in a crash. Predator population declines due to lack of food.

Antipredator Defenses Prey have evolved strategies to escape predation Coevolution: two species adapting in response to selective pressure imposed by each other Sharp spines of cacti Pointed leaves of holly Leathery leaves of oak tree All discourage predation by insects Prey escape predation by utilizing camouflage, poisonous secretions, fright, flocking together, warning coloration, and mimicry.

Mimicry Occurs when one species resembles another species or an object in environment to escape predation There are 2 types of mimicry: Batesian mimicry: prey that is not harmful mimics another species that is harmful. Ex. Flower fly & beetle will look like stinging wasp 2. Mullerian mimicry: both species that look alike have good defenses Ex. Bumble bee & wasp

Symbiosis Refers to close interactions between members of two different species Three types of symbiotic relationships are: Parasitism: (+) (-) the parasite gets nourishment from another organism called the host. Ex. Leeches, ticks, tapeworms Commensalism: (+) (0) one species benefits, the other species is neither harmed nor helped. Ex. Barnacles on whales, clownfish/anenomes 3. Mutualism: (+) (+) both species in the association benefit. Ex. Ants & bullhorn acacia tree, plants & animal pollinators