Species Interactions in an Ecosystem Populations and Species Interactions in an Ecosystem

A habitat differs from a niche. A habitat is all aspects of the area in which an organism lives. (location) An ecological niche includes all of the factors that a species needs to survive, stay healthy, and reproduce. (Role in ecosystem) food Behavior 2

Competition occurs when two species use resources in the same way. Competitive exclusion keeps two species from occupying the same niche. Competitive exclusion has different outcomes. Resource availability gives structure to a community. 1) One species is better suited to the niche and the other will either be pushed out or become extinct. 2) The niche will be divided. The two species will further diverge. 3

Intraspecific competition (between SAME Species; Mates) Competition and predation are two important ways in which organisms interact. Competition occurs when two organisms fight for the same limited resource. Intraspecific competition (between SAME Species; Mates) Interspecific competition (between 2 Different Species; Food) 4

Predation occurs when one organism captures and eats another. 5

There are three major types of symbiotic relationships. 1) Mutualism: both organisms benefit (+/+) 6

2) 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 7

3) Parasitism: one organism benefits, the other is harmed _ 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 + 8

Parasitism meet their needs as ectoparasites (such as leeches) and endopaasites (such as hookworms)

Scientists can calculate population density. Population density is the number of individuals that live in a defined area. Scientists can calculate population density. 10

Population dispersion refers to how the individuals in a population are spread in an area. Clumped dispersion Uniform Random 11

Survivorship curves help to describe the reproductive strategy of a species & is a diagram showing the number of surviving members over time from a measured set of births. 12

Survivorship curves can be type I, II or III. Type I —low level of infant mortality and an older population; large mammals and humans Type II—survivorship rate is equal at all stages of life; birds and reptiles Type III—very high birth rate, very high infant mortality; insects, fish and plants 13

Changes in a population’s size are determined by four factors: immigration, births, emigration, and deaths. The size of a population is always changing. Population growth is based on available resources. 14

Exponential growth is a rapid population increase due to an abundance of resources. (J- shaped curve) 15

Logistic growth is due to a population facing limited resources Logistic growth is due to a population facing limited resources. (S shaped curve) Carrying capacity is the maximum number of individuals in a population that the environment can support; Limits pop. growth 16

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. 17

Competition (food/shelter) parasitism Density-dependent limiting factors are affected by the number of individuals in a given area. Predation Disease Competition (food/shelter) parasitism 18

Animation of limiting factors Density-independent limiting factors limit a population’s growth regardless of the density. unusual weather natural disasters human activities Animation of limiting factors 19

Succession occurs following a disturbance in an ecosystem. a sequence of biotic changes damaged communities are regenerated new communities arise in previously uninhabited areas

There are two types of ecological succession. primary succession — started by pioneer species (lichens); bare rock- nothing living there before:

There are two types of succession. secondary succession — started by remaining species; once living things; soil still intact