Chapter 8 Understanding Populations Section 1: How Populations Change in Size

What is a Population? Members of the same species living in the same place at the same time. A reproductive group. Examples: bass in an Iowa lake palm trees on an island

Properties of Populations Size Density= number of individuals per unit area or volume example: 14 birds = 7 birds per acre 2 acres 3. Dispersion- the relative distribution or arrangement of individuals within a given amount of space. —3 types….

Clumped Dispersion Individuals live close together in groups for mating purposes, protection, or food resources Clumped dispersion

Uniform Dispersion Individuals live at specific distances from one another Uniform dispersion 

Random Dispersion Individuals are spread randomly within an area

Factors determine the size of a population Immigration: movement of individuals into a population Emigration: movement of individuals out of a population Births: increase the size of a population Deaths: decrease the size of a population

positive growth rates: more births, less deaths zero growth rates: births = deaths negative growth rates- more deaths, less births

Reproductive Potential: biotic potential: the fastest rate at which a population can grow---this is limited by reproductive potential. Reproductive potential: maximum number of offspring that a given organism can produce. Some species have higher reproductive potential than others.-- Ex. Bacteria and insects have a high reproductive potential , while elephants have a low one

Reproductive potential increases when individuals produce more offspring at a time, reproduce more often, and reproduce earlier in life. Reproducing earlier in life has the greatest effect on reproductive potential. Reproducing early shortens the generation time, or the average time it takes a member of the population to reach the age when it reproduces.

Reproductive Potential con’t. Small organisms, such as bacteria and insects, have short generation times and can reproduce when they are only a few hours or a few days old. As a result, their populations can grow quickly. In contrast, large organisms, such as elephants and humans, become sexually mature after a number of years and therefore have a much lower reproductive potential than insects. Most organisms have a reproductive potential that far exceeds the number of their offspring that will survive. Ex. sea turtles, frogs

Population growth is based on available resources 2 types of population growth - exponential growth - logistic growth

Exponential Growth Population grows rapidly due to abundant resources bacteria or molds grow on a new source of food. J-shaped curve

Logistic Growth Population begins with slow growth followed by exponential growth then levels off due to limited resources S-shaped curve

What Limits Population Growth? a. resources being used up b. environment changes c. deaths increase or births decrease d. Natural selection

Carrying Capacity: maximum amount of individuals that an environment can support A population may increase beyond this number but it cannot stay at this increased size. Reached when a particular natural resource is consumed at the same rate at which the ecosystem produces the resource = limiting resource

Carrying Capacity Example of carrying capacity: rabbits in Australia page 214

Ecological factors regulate population growth Limiting factor: something that keeps the size of a population down 2 types of limiting factors 1. density-dependent 2. density-independent

Density-dependent limiting factors affect a population that has become overcrowded Competition Predation Parasitism & disease The greater the population, the greater effect these factors have. Ex. Black plague in the Middle Ages – more deaths in cities Page 216- beetles spreading disease to pine trees

Density-independent limiting factors limit a population’s growth regardless of the density. Unusual weather Natural disasters Human activities -Most are abiotic factors -Page 216- winter storm freezing crops and fruiting trees (regardless of density)

Section 2: How Species Interact with Each Other

A habitat differs from a niche. Habitat: where an organism lives includes - biotic factors & - abiotic factors

- food (type, how it gets it, where is it in the food web) Niche: includes all of the factors that a species needs to survive, stay healthy, and reproduce - food (type, how it gets it, where is it in the food web) - abiotic conditions (temp., amount of water it needs) - behavior (when is it active, when does it reproduce) **A habitat is where a species lives and a niche is how it lives within its habitat.

A lion must hunt and kill its prey in order to survive on the African savannah. Its role as a top predator is part of the lion’s niche. The lion may use the tall grass as camouflage, and hunt primarily at dawn or dusk. It also spends afternoons in the shade. All of this helps define its “ecological niche”.

Competition occurs when organisms fight for the same limited resources Two types of competition: - Interspecific: 2 different species compete for a limited resource - Intraspecific: individuals from the same species compete for a limited resource

Ways some species adapt to competition: Competitive Exclusion Principal- states that when two species are competing for the same resources, one species will be better suited to the niche, and the other species will be pushed into another niche or become extinct. (Also known as niche restriction)

potential niche- total niche a species can occupy realized niche- where species is actually found

Another example: North American gray squirrel European red squirrel

Predation occurs when one organism captures and eats another

When predators eat only specific types of prey, the sizes of each population tend to increase and decrease in linked patterns, as shown below. Ex. Canadian Lynx and snowshoe hare

Symbiosis means “living (biosis) together (sym)” = It is a close ecological association between two or more organisms of different species. 3 Types of symbiosis: - mutualism - commensalism - parasitism

Mutualism: both organisms benefit - Bat eats cactus and spreads seeds to new locations

bees get nectar from the plant and the plant is pollinated

Acacia tree and red ants: ants provide protection from other organisms trying to feed on the tree and the ants receive a home and nectar.

Tickbird feeds off insects on rhinos Back; rhino gets irritating bugs picked off hide = both benefit

Commensalism: one organism benefits, the other is unaffected 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

Sea anemone and clown fish- Fish feeds on scraps of food that come out the anemones mouth. The sea anemone receives nothing in return

Orchids growing in tops of trees- The orchids grow around the tree trunks and do not harm the tree. The orchid is exposed to sunlight and rain.

Parasitism: one organism benefits (parasite), the other is harmed (host) + _ Organism is harmed 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

Other examples of parasites: ticks, fleas, tapeworms, leeches, mistletoe.