Populations and Community Ecology
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Transcript of Populations and Community Ecology
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