Populations and Community EcologyChapter 19 and Chapter 20

Population- group of organisms that belong to the same species and live in a particular place at the same time

Population Density- measures how crowded a population is; the number of individuals per unit of area or volumeWhen counting the plants in a forest, measure and rope out a

small section to count all the species in that section, then take that information to estimate the total population for the entire forest.

Dispersionfrom Latin word dis- meaning “out” and spargere meaning “to scatter”

- the pattern of spacing among individuals within geographic population

• clumped

• uniform

• random

- clustered individuals

- separated by a fairly consistence distance

- location is independent of locations of other individuals

Population Dynamics- change in size and composition over time

BIRTH RATE

DEATH RATE

LIFE EXPECTANCY

- # of births occurring in a period of time

- mortality rate; # of deaths occurring in a period of time

- how long an average of individual is expected to live

Age Structure- distribution of individuals among different ages in a population; young population means potential for rapid growth

Growth Rate- amount by which a populations’ size changes in a given time

4growth, shrinking, or remaining the same depends on: 1. births

2. deaths3. emigration4. immigration

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GROWTH RATE = BIRTH RATE – DEATH RATEif growth rate is positiveif growth rate is negative

- population growing- population shrinking

Exponential Growth – a pattern of increase in a # due to a steady growth rate

Growth Rate ExampleIn a certain population there is 52 births and 14 deaths per 1000 individuals in one year.

Birth rate = 52/1000Death rate = 14/1000

growth rate = 0.052 – 0.014= 0.038 (growth per capita)

Exponential Model• J-shaped curve• population size grow slowly when small but speeds up as individuals join• predicts pop. size will increase indefinitely• does not apply to most populations• in natural environments:

pops. cannot grow indef.

limiting factor – anything that restrains growth

Logistic Model• S-shaped curve• builds on exponential model• takes the influencing limiting factors into account

Carrying Capacity- (K); the # of individuals the environment can support over a long period of time

• at carrying capacity birth & death rates are equal, growth rate stops • assumption: capacity is constant & does not fluctuate with environmental changes

Population Fluctuations

Density-independent factors – reduces the population by same proportions, regardless of size

Density-dependent factors – resources are limited; depends on the # of individuals in same area

Ex. weather, floods, fire

Ex. shortages of food or nesting sites

BottleneckModel

• small populations less genetic variation

Relationships between OrganismsPREDATION

- an individual in one species (predator) eats all or part of an individual of another species (prey)- relationship influences size of each population and affects where and how each species live

• all heterotrophs are either predators or parasites or both

• natural selection favors the evolution of adaptations for finding, capturing, and consuming prey• example:

Rattlesnake – acute sense of smell and heat sensitive pits below each nostril

- can detect warm bodied prey in dark

• predators survival depends on its ability to capture food, but prey’s survival depends on its ability to avoid being captured

Adaptationsin Animal Prey

- flee- hiding or resembling an

inedible object - deceptive markings,

chemical defenses (produce toxins, bright colors)

MIMICRY – one species closely resembles another species

Adaptationsin Plant Prey

- cannot run away- physical defenses = sharp thorns, spines, sticky

hairs, touch leaves- chemical defenses =poisonous, irritating or bad

tasting

Competition• interspecific competition

- 2 or more species use the same limited resource• competitive exclusion

- one species is eliminated from a community because of competition for the same limited resource

Relationships between OrganismsSYMBIOSIS

- close, long-term relationship between 2 organism

1. parasitism

2. mutualism

3. commensalism

- one individual is harmed while the other benefits- both organisms derive some benefit

- one organism benefits, the other is neither helped nor harmed

Parasitism• host is harmed• parasite benefits does not result in immediate death of host

ECTOPARASITES

ENDOPARASITES

- outside of the host

- inside of the host

parasite – Latin word parasites meaning “one who eats t the table of another”

Ex. heartworms, disease-causing protists, tapeworms

Ex. lice, leeches, fleas, ticks, mosquitoes

Mutualism- some relationships are so close that neither species can survive without the other

• pollination – one of the most important type of mutualism• bees, butterflies, beetles, bats, & birds carry

pollen between flowering plants (pollinators)• flower is a lure; color pattern, shape, scent• plant provides food (nectar or pollen)

Example: acacia tree and ants

Commensalism- one benefits the other neither harmed nor helped- scavengers are often considered to have this kind of symbiosis

Example:cattle egrets and water buffalo

Ecological Successionsuccession – from Latin succeder meaning “to go beneath” or “to follow after”- gradual, sequential re-growth of a community of species in an area

• primary succession – development of a community in an area that has not supported life previously• ex. bare rock, sand dune, island, etc

• secondary succession – sequential replacement of species that follows a disruption (events that change communities, remove or destroy organisms from communities, or alters resource availability) of an existing community

PIONEER SPECIES – species of organisms that predominate early in succession; tend to be small and grow quickly

CLIMAX COMMUNITY – community that reaches a stable end point