Interactions in Ecosystems Chapter 14

KEY CONCEPT Every organism has a habitat and a niche.

A habitat differs from a niche. A habitat is all aspects of the area in which an organism lives. – biotic factors – abiotic factors An ecological niche includes all of the factors that a species needs to survive, stay healthy, and reproduce. –food –abiotic conditions –behavior

Resource availability gives structure to a community. Species can share habitats and resources. Competition occurs when two species use resources in the same way—competitive exclusion Competitive exclusion keeps two species from occupying the same niche—one species will be better suited to the niche.

Competitive exclusion has different outcomes. –One species is better suited to the niche and the other will either be pushed out or become extinct. –The niche will be divided. –The two species will further diverge.

Ecological equivalents are species that occupy similar niches but live in different geographical regions. Madagascar South America

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

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

–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 Ø Organism is not affected Commensalism There are three major types of symbiotic relationships.

– Parasitism: one organism benefits, the other is harmed There are three major types of symbiotic relationships. Organism benefits 0 _ 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 + 0

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. Clumped dispersion Uniform dispersion Random dispersion

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

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

Immigration vs Emigration Immigration—movement of individuals into a population from another population Example: two fruit flies entering your backpack to sit on a banana Emigration—movement of individuals out of a population and into another population Examples—two fruit flies exited your backpack to find other fruit

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.

–parasitism and disease –predation –competition

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

KEY CONCEPT Ecological succession is a process of change in the species that make up a community.

Succession occurs following a disturbance in an ecosystem. Succession regenerates or creates a community after a disturbance. – a sequence of biotic changes – damaged communities are regenerated – new communities arise in previously uninhabited areas

There are two types of succession. –primary succession — started by pioneer species

There are two types of succession. –secondary succession — started by remaining species