KEY CONCEPT Organisms interact as individuals and as populations.

Competition and predation are two important ways in which organisms interact. Competition occurs when two organisms fight for the same limited resource. Intraspecific competition Interspecific competition

Predation occurs when one organism captures and eats another.

There are three major types of symbiotic relationships. Mutualism: both organisms benefit

There are three major types of symbiotic relationships. Commensalism: one organism benefits, the other is unharmed Human Our eyelashes are home to tiny mites that feast on oil secretions and dead skin. Without harming us, up to 20 mites may be living in one eyelash follicle. Demodicids Eyelash mites find all they need to survive in the tiny follicles of eyelashes. Magnified here 225 times, these creatures measure 0.4 mm in length and can be seen only with a microscope. + Organism benefits Ø Organism is not affected Commensalism

There are three major types of symbiotic relationships. Parasitism: one organism benefits, the other is harmed Organism benefits _ Organism is not affected Hornworm caterpillar The host hornworm will eventually die as its organs are consumed by wasp larvae. Braconid wasp Braconid larvae feed on their host and release themselves shortly before reaching the pupae stage of development. Parasitism +

There are three major types of symbiotic relationships. Parasitism meet their needs as ectoparasites (such as leeches) and endopaasites (such as hookworms)

KEY CONCEPT Each population has a density, a dispersion, and a reproductive strategy.

Population density is the number of individuals that live in a defined area. Population density is a measurement of the number of individuals living in a defined space. Scientists can calculate population density.

Population dispersion refers to how a population is spread in an area. Geographic dispersion of a population shows how individuals in a population are spaced. Population dispersion refers to how a population is spread in an area. Clumped dispersion Uniform Random

There are three types of dispersion. clumped

There are three types of dispersion. uniform

There are three types of dispersion. random

Survivorship curves help to describe the reproductive strategy of a species. A survivorship curve is a diagram showing the number of surviving members over time from a measured set of births.

Survivorship curves can be type I, II or III. Type I—low level of infant mortality and an older population common to large mammals and humans Type II—survivorship rate is equal at all stages of life common to birds and reptiles Type III—very high birth rate, very high infant mortality common to invertebrates and plants

KEY CONCEPT Populations grow in predictable patterns.

Changes in a population’s size are determined by immigration, births, emigration, and deaths. The size of a population is always changing. Four factors affect the size of a population. immigration births emigration deaths

Population growth is based on available resources. Exponential growth is a rapid population increase due to an abundance of resources.

Logistic growth is due to a population facing limited resources.

Carrying capacity is the maximum number of individuals in a population that the environment can support. A population crash is a dramatic decline in the size of a population over a short period of time.

Ecological factors limit population growth. A limiting factor is something that keeps the size of a population down. Density-dependent limiting factors are affected by the number of individuals in a given area.

Density-dependent limiting factors are affected by the number of individuals in a given area. predation competition parasitism and disease

Density-independent limiting factors limit a population’s growth regardless of the density. unusual weather natural disasters human activities