Populations and Community Ecology
· Population- is a group of organisms that belong to the same species and live in a particular place.
· Population density- measures how crowded a population is.
· Dispersion- the spatial distribution of individuals within the population.
o Clumped distribution- individuals are clustered together
§ Occur when food and resources are clumped
§ Also occurs if animals live together in herds or flocks
o Uniform distribution- individuals are separated by a fairly consistent distance
§ Social behavior causes them to live apart
o Random distribution- each individuals location is independent of the location of the other individuals in the population
· Population Dynamics- Populations change in size and composition over time. There are a number of factors scientists use to determine populations in an ecosystem
o Birth Rate- The number of births occurring in a period of time.
o Death Rate- or mortality rate is the number of deaths in a period of time.
o Life Expectancy- how long on average an individual is expected to live.
· Population Growth Rate is the amount by which a population’s size changes over time.
o Whether a population grows, shrinks, or remains the same depends on four processes:
§ Birth rate
§ Death rate
§ Immigration – the movement of individuals into a population
§ Emigration –the movement of individuals out of a population
o Population size can be summed up by the equation
§ Birth rate – death rate = growth rate
· Population Regulations- There are two kinds of limiting factors which control population size;
o Density independent factors-
§ Examples: weather, floods, and fires
o Density Dependent factors- include resource limitations such as;
§ Shortages of food or shortages of nesting sites
o Perils of small populations-
§ A rise in human population has caused many species populations to decrease
§ Environmental disturbances can kill off the entire population or leave too few individuals to maintain the population. Such factors include; storms, fires, floods, or disease outbreaks
§ As populations decrease in size it increases the risk of inbreeding, or mating with rleatives
· Community Ecology
o Predation- an individual of one species, called the predator, eats all or part of another species, called the prey. It helps control population size in an ecosystem.
§ Predator Adaptations
· Good eye sight, hearing, sense of smell
· Sharp claws and teeth
· Fast
· Camouflage
§ Animal Prey Adaptations
· Good eye sight, hearing, sense of smell
· Camouflage
· Mimicry
· Nocturnal
· Bad odor
§ Plant Prey Adaptations
· Sharp thorns, spines, sticky hairs, tough leaves
· Poisonous, irritating, or bad taste(poison ivy)
· Symbiosis is a close, long term relationship between two organisms.
o Three examples of symbiotic relationships
§ Parasitism-One individual is harmed while the other individual benefits.
· The host is harmed while the parasite benefits.
· Ectoparasites are parasites that live on their host(outside)
o Examples of Ectoparasites are lice, leeches, fleas, ticks, and mosquitoes.
· Endoparasites live in their host.
o Examples are heartworm and tapeworm
§ Mutualism- Two species derive benefit from each other.
· Some relationships are so close that neither can live without the other.
· Pollination is a good example. Bees benefit from taking pollen and the flower gets pollinated from the bee.
§ Commensalism-One species benefits while the other neither benefits nor is harmed.
· Egrets benefit from the movement of buffaloes across a field. The buffalo stir up insects that the egrets eat.
· Successional Changes in Communities
o Ecological succession- The gradual, sequential re-growth of a community of species. There are two types:
§ Primary succession- is the development of a community in an area that has not previously supported life such as a barren rock, sand dune, or island formed by volcanic activity
· Example: Repeated freezing and thawing of rocks produces enough soil for lichens to grow. A lichen is a mutualistic relationship between fungi and algae
§ Secondary succession- the sequential replacement of species that follows the disruption of an existing community. It occurs where soil already exists
§ Pioneer species- the species of organisms that pre-dominate early succession. They tend to be small , grow quickly, and reproduce quickly. They are well suited for the disturbed area.
§ Climax community- is a stable end point to succession. It will remain constant for a long period of time.