Chapter 8 Chapter 8 Environmental Environmental

Science Science

UnderstandiUnderstanding ng

PopulationsPopulations

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ObjectivesObjectives DescribeDescribe the three main properties of a the three main properties of a

population.population. DescribeDescribe exponential population exponential population

growth.growth. DescribeDescribe how the reproductive how the reproductive

behavior of individuals can affect the behavior of individuals can affect the growth rate of their population.growth rate of their population.

ExplainExplain how population sizes in nature how population sizes in nature are regulated.are regulated.

How Populations Change in How Populations Change in SizeSize

Charles Darwin calculated that a Charles Darwin calculated that a single pair of elephants could single pair of elephants could theoretically produce 19 million theoretically produce 19 million descendants within 750 years, descendants within 750 years, making the point that the actual making the point that the actual number of elephants is limited by number of elephants is limited by their environment.their environment.

A. What is a Population?A. What is a Population?

PopulationPopulation – all the members of a – all the members of a species living in the same place at species living in the same place at the same timethe same time

-a population is a reproductive group -a population is a reproductive group because organisms usually breed because organisms usually breed with members of their own with members of their own populationpopulation

-population also refers to the size – -population also refers to the size – or number of individuals it containsor number of individuals it contains

B. Properties of B. Properties of PopulationsPopulations

Populations can be described in Populations can be described in terms of size, density, or dispersionterms of size, density, or dispersion

DensityDensity – the number of individuals – the number of individuals per unit area or volumeper unit area or volume

DispersionDispersion – relative distribution or – relative distribution or arrangement of its individuals within arrangement of its individuals within a given amount of spacea given amount of space

-dispersion may be -dispersion may be even, even, clumped,clumped, or or randomrandom

C. How Does a Population C. How Does a Population Grow?Grow?

A population grows with births and A population grows with births and shrinks with deaths.shrinks with deaths.

Population change over time is Population change over time is represented by:represented by:

Growth rateGrowth rate

Growth rateGrowth rate – change in a – change in a population’s size over timepopulation’s size over time

Over time, the growth rates change Over time, the growth rates change in a population because birth and in a population because birth and death rates increase or decreasedeath rates increase or decrease

Growth rates can be positive, Growth rates can be positive, negative, or zeronegative, or zero

for a zero population growth the average for a zero population growth the average number of births must equal the average number of births must equal the average number of deathsnumber of deaths

-a population would remain the same -a population would remain the same size if each pair of adults produced exactly size if each pair of adults produced exactly two offspring and each of those offspring two offspring and each of those offspring survived to reproducesurvived to reproduce

-if the adults in a population are not -if the adults in a population are not replaced by new births, the growth rate replaced by new births, the growth rate will be negative and the population will will be negative and the population will shrinkshrink

D. How Fast Can a D. How Fast Can a Population Grow?Population Grow?

Populations usually stay about the Populations usually stay about the same size from year to year because same size from year to year because various factors kill many individuals various factors kill many individuals before they can reproduce before they can reproduce

Biotic potentialBiotic potential

Biotic potentialBiotic potential – the fastest rate at – the fastest rate at which its populations can growwhich its populations can grow

-this number is limited by the -this number is limited by the maximum number of offspring that maximum number of offspring that each member of the population can each member of the population can produce – produce – reproductive potentialreproductive potential

Reproductive PotentialReproductive Potential some species have much higher reproductive some species have much higher reproductive

potentials than otherspotentials than others

-750 years for a pair of elephants to -750 years for a pair of elephants to produce produce 19 million descendants 19 million descendants

It takes a few days or weeks for a single It takes a few days or weeks for a single bacterium to produce 19 million descendantsbacterium to produce 19 million descendants

Reproductive potential increases whenReproductive potential increases when

-individuals produce more offspring at a -individuals produce more offspring at a timetime

-reproduce more often-reproduce more often

-reproduce earlier in life – this has the -reproduce earlier in life – this has the greatest effect on reproductive potential greatest effect on reproductive potential

Early reproduction shortens the Early reproduction shortens the generation timegeneration time – the average time it – the average time it takes for member of the population to takes for member of the population to reach the age when it reproducesreach the age when it reproduces

Small organisms like bacteria and insects Small organisms like bacteria and insects have short generation timeshave short generation times

-they can reproduce when they are a -they can reproduce when they are a few few hours or days oldhours or days old

-their populations can grow quickly-their populations can grow quickly Large organisms like elephants and Large organisms like elephants and

humans become sexually mature after a humans become sexually mature after a number of yearsnumber of years

Human generation time is about 20 years Human generation time is about 20 years so humans have a much lower so humans have a much lower reproductive potentialreproductive potential

Exponential GrowthExponential Growth In exponential In exponential

growth, a large growth, a large number of number of individuals is individuals is added to the added to the population in population in each succeeding each succeeding time period.time period.

Exponential growthExponential growth

Exponential growthExponential growth – when a – when a population grows faster and fasterpopulation grows faster and faster

-graph represents a J-curve-graph represents a J-curve -occurs in nature only when -occurs in nature only when

populations have plenty of food and populations have plenty of food and space and have no competition or space and have no competition or predatorspredators

E. What Limits Population E. What Limits Population Growth?Growth?

Because natural conditions are neither Because natural conditions are neither ideal nor constant, populations cannot ideal nor constant, populations cannot grow forever and rarely grow at their grow forever and rarely grow at their reproductive potentialreproductive potential

-eventually resources are used up or the -eventually resources are used up or the environment changes, and deaths environment changes, and deaths increase or births decreaseincrease or births decrease

-under the forces of nature only some -under the forces of nature only some members of a given population will survive members of a given population will survive and reproduce, thus the properties of a and reproduce, thus the properties of a population may change over timepopulation may change over time

Carrying capacityCarrying capacity Carrying capacityCarrying capacity – the maximum – the maximum

population that the ecosystem can support population that the ecosystem can support indefinitelyindefinitely

-a population may increase beyond this -a population may increase beyond this number, but it cannot stay that way for longnumber, but it cannot stay that way for long

-because ecosystems change it is difficult to -because ecosystems change it is difficult to predict or calculate exactlypredict or calculate exactly

-can be estimated by looking at average -can be estimated by looking at average population sizes or by observing a population population sizes or by observing a population crash after a certain size has been exceededcrash after a certain size has been exceeded

example: example: Rabbits in AustraliaRabbits in Australia are the most are the most serious serious mammalian pests, an , an invasive species whose destruction of habitats are responsible for whose destruction of habitats are responsible for the extinction or major decline of many native the extinction or major decline of many native animals animals

Resource limitsResource limits

a species reaches its carrying capacity a species reaches its carrying capacity when it consumes a particular natural when it consumes a particular natural resource at the same rate at which the resource at the same rate at which the ecosystem produces the resource called ecosystem produces the resource called the the limiting resourcelimiting resource

plant growth is limited by supplies of plant growth is limited by supplies of water, sunlight, and mineral nutrientswater, sunlight, and mineral nutrients

-supply of the most severely limited -supply of the most severely limited resources determines the carrying resources determines the carrying capacity of an environment for a particular capacity of an environment for a particular species at a particular timespecies at a particular time

Carrying CapacityCarrying Capacity

CompetitionCompetition -members of a population use the same -members of a population use the same

resources in the same ways so they will resources in the same ways so they will eventually compete with one another as the eventually compete with one another as the population approaches its carrying capacitypopulation approaches its carrying capacity

-instead of competing for a resource such -instead of competing for a resource such as food, individuals can compete for as food, individuals can compete for territoryterritory

--territoryterritory – an area defended by one or – an area defended by one or more individuals against other individualsmore individuals against other individuals

area valuable for the shelter, food, or area valuable for the shelter, food, or breeding sites it containsbreeding sites it containscompetition is part of the pressure of competition is part of the pressure of

natural natural selection selection

F. Two Types of Population F. Two Types of Population RegulationRegulation

Population size can be limited in Population size can be limited in ways that may or may not depend on ways that may or may not depend on the density of the populationthe density of the population

causes of death in a population can causes of death in a population can be be density-dependent density-dependent or or density-density-independentindependent

Density-dependentDensity-dependent

Density-dependentDensity-dependent – when deaths – when deaths occur more quickly in a crowded occur more quickly in a crowded population than in a sparse populationpopulation than in a sparse population

-happens when individuals in a population -happens when individuals in a population are densely packed together such as are densely packed together such as when a population is growing rapidlywhen a population is growing rapidly

-competition for resources, mates, -competition for resources, mates, diseasedisease

Density-independentDensity-independent

Density-independentDensity-independent – when a – when a certain proportion of a population dies certain proportion of a population dies regardless of the population’s sizeregardless of the population’s size

-this type of regulation affects all -this type of regulation affects all populations in a general or uniform waypopulations in a general or uniform way

-severe weather, natural disasters, etc.-severe weather, natural disasters, etc.

Quick LABQuick LAB

Math PracticeMath Practice

BellringerBellringer

ObjectivesObjectives ExplainExplain the difference between niche the difference between niche

and habitat.and habitat. GiveGive examples of parts of a niche. examples of parts of a niche. DescribeDescribe the five major types of the five major types of

interactions between species.interactions between species. ExplainExplain the difference between the difference between

parasitism and predation.parasitism and predation. ExplainExplain how symbiotic relationships how symbiotic relationships

may evolve.may evolve.

II. How Species Interact II. How Species Interact with Each Otherwith Each Other

A. An Organism’s NicheA. An Organism’s Niche

NicheNiche – the unique role of a species – the unique role of a species within an ecosystemwithin an ecosystem

-includes the species’ physical home, -includes the species’ physical home, environmental factors necessary for environmental factors necessary for the species’ survival, all of the the species’ survival, all of the

other species’ interactions with other other species’ interactions with other organismsorganisms

NicheNiche

-a niche is different from a habitat – -a niche is different from a habitat – habitat is location, but niche is an habitat is location, but niche is an organism’s pattern of use of its organism’s pattern of use of its habitathabitat

-the functional role, or job of a -the functional role, or job of a particular species in an ecosystemparticular species in an ecosystem

B. Ways in Which Species B. Ways in Which Species InteractInteract

The five major types of species The five major types of species interactioninteraction– competition, predation, parasitism, competition, predation, parasitism,

mutualism, and commensalismmutualism, and commensalism Based on whether each species causes Based on whether each species causes

benefit or harm to the other speciesbenefit or harm to the other species

Many interactions cannot be Many interactions cannot be categorized or well studiedcategorized or well studied

Species InteractionsSpecies Interactions

C. CompetitionC. Competition CompetitionCompetition – a relationship in which – a relationship in which

different individuals or populations different individuals or populations attempt to use the same limited attempt to use the same limited resourceresource

-each individual has less access to the -each individual has less access to the resource and so is harmed by the resource and so is harmed by the competitioncompetition

-competition can occur both within -competition can occur both within and between speciesand between species

2 Types of Competition2 Types of Competition --intraspecific competitionintraspecific competition – occurs – occurs

among individuals of the same speciesamong individuals of the same speciesEx: Deer against DeerEx: Deer against Deer

--interspecific competitioninterspecific competition – occurs – occurs between different speciesbetween different species

Ex: Deer against RabbitEx: Deer against Rabbit

-members of the same species must -members of the same species must compete with each other because they compete with each other because they require the same resources because they require the same resources because they occupy the same nicheoccupy the same niche

OverlapOverlap --overlapoverlap – when – when

members of members of different species different species compete for the compete for the same resources same resources their niches their niches overlapoverlap

-each species -each species uses some of uses some of the same the same resources in a resources in a habitathabitat

Resource use

Species 1 Species 2

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Indirect competitionIndirect competition

-species can compete even if they never -species can compete even if they never come into direct contact with each othercome into direct contact with each other

-if one insect species feeds on a certain -if one insect species feeds on a certain plant during the day and another species plant during the day and another species on the same plant at nighton the same plant at night

-two plants that flower at the same time -two plants that flower at the same time compete for pollinatorscompete for pollinators

-humans and the insects that eat our -humans and the insects that eat our crops – both compete for the same cropscrops – both compete for the same crops

Adaptations to competitionAdaptations to competition -when two species with similar niches are -when two species with similar niches are

placed together in the same ecosystem placed together in the same ecosystem

-one species will probably be more -one species will probably be more successful than anothersuccessful than another

-the better adapted would be able to use -the better adapted would be able to use more of the nichemore of the niche

-during the course of evolution -during the course of evolution adaptations that decrease competition adaptations that decrease competition would be advantageous for those species would be advantageous for those species whose niche’s overlapwhose niche’s overlap

Adaptations to CompetitionAdaptations to Competition

Law of competitive Law of competitive exclusionexclusion

Law of competitive exclusionLaw of competitive exclusion – no two – no two species can occupy the same ecological species can occupy the same ecological niche for very longniche for very long

Competition can be reduced between species Competition can be reduced between species is by dividing up the niche in time or spaceis by dividing up the niche in time or space

--niche restrictionniche restriction – when each species uses – when each species uses less of the niche than they are capable of less of the niche than they are capable of usingusing

Sharing observed in closely related Sharing observed in closely related species that use the same resources species that use the same resources within a habitat-within a habitat-resource resource partitioningpartitioning

Cape May Warbler

Black-throated Green Warbler

Yellow-rumped Warbler

Bay-breasted Warbler

D. PredationD. Predation PredationPredation – an organism that feeds on – an organism that feeds on

another organism another organism

predatorpredator – the organism that eats, – the organism that eats, preyprey – – the organism that gets eatenthe organism that gets eaten

Food webs can make predation a Food webs can make predation a complicated interaction, the prey of one complicated interaction, the prey of one species can be the predator of anotherspecies can be the predator of another

Most organisms have evolved some Most organisms have evolved some mechanisms to avoid or defend against mechanisms to avoid or defend against predatorspredators

CASE STUDYCASE STUDY camouflagecamouflage, toxic chemicals, , toxic chemicals,

warning colorationwarning coloration, , mimicrymimicry – 2 – 2 types, types, protective coveringprotective covering

Predator/prey populations tend to Predator/prey populations tend to fluctuate togetherfluctuate together

PredatorsPredators Some predators Some predators

eat only specific eat only specific types of prey. In types of prey. In this kind of close this kind of close relationship, the relationship, the sizes of each sizes of each population tend population tend to increase and to increase and decrease in decrease in linked patterns, linked patterns, as shown below.as shown below.

E. ParasitismE. Parasitism ParasiteParasite – an organism that lives in – an organism that lives in

or on another organism and feeds on or on another organism and feeds on it it

HostHost – the organism the parasite – the organism the parasite takes its nourishment fromtakes its nourishment from

ParasitismParasitism – the relationship – the relationship between the parasite and the hostbetween the parasite and the host

Bed Bugs Bed Bugs

ParasitesParasites ticks, fleas, tapeworms, heartworms, ticks, fleas, tapeworms, heartworms,

bloodsucking leeches, and mistletoebloodsucking leeches, and mistletoe Somewhat like predators except Somewhat like predators except

parasites spends some or all of its life in parasites spends some or all of its life in or on its host, and do not usually kill or on its host, and do not usually kill their hosttheir host

A parasite can have an evolutionary A parasite can have an evolutionary advantage if it allows its host to live advantage if it allows its host to live longerlonger

Usually the host is weakened or Usually the host is weakened or exposed to disease by the parasiteexposed to disease by the parasite

MistletoeMistletoe

MistletoeMistletoe Mistletoes have specialized roots with the ability to Mistletoes have specialized roots with the ability to

penetrate a host plant and absorb nutrients. Most penetrate a host plant and absorb nutrients. Most mistletoe species are either full parasites like dwarf mistletoe species are either full parasites like dwarf mistletoes (mistletoes (Arceuthobium Arceuthobium spp.) or partial parasites, spp.) or partial parasites, called hemiparasites, like the mistletoes (called hemiparasites, like the mistletoes (Viscum Viscum and and Phoradendron Phoradendron spp.) used for holiday decoration.spp.) used for holiday decoration.

Hemiparasites get a portion of their nourishment Hemiparasites get a portion of their nourishment from their host, but they also contain chlorophyll, from their host, but they also contain chlorophyll, making them green and giving them the ability to making them green and giving them the ability to conduct photosynthesis and make some sugars for conduct photosynthesis and make some sugars for themselves. The berries of most mistletoe species themselves. The berries of most mistletoe species are white, but they can also be yellowish or even are white, but they can also be yellowish or even pink to red. Most parts of a mistletoe plant are toxic pink to red. Most parts of a mistletoe plant are toxic and should not be eaten. and should not be eaten.

F. MutualismF. Mutualism MutualismMutualism - a close relationship - a close relationship

between two species in which each between two species in which each species provides a benefit to the other species provides a benefit to the other

-certain species of bacteria in the -certain species of bacteria in the intestines of humansintestines of humans

-they help break down food, provide -they help break down food, provide with vitamins and we provide it with a with vitamins and we provide it with a warm, food-rich habitatwarm, food-rich habitat

Ant & acacia trees in Central AmericaAnt & acacia trees in Central America

G. CommensalismG. Commensalism

CommensalismCommensalism –a relationship in –a relationship in which one species benefits and the which one species benefits and the other is neither harmed nor helpedother is neither harmed nor helped– sharks and a fish called remoras – sharks and a fish called remoras –

attach to sharks and feed on scraps of attach to sharks and feed on scraps of food left over from their meals food left over from their meals

– when birds nest in treeswhen birds nest in trees

H. Symbiosis and H. Symbiosis and CoevolutionCoevolution

SymbiosisSymbiosis – a relationship in which – a relationship in which two organisms live in close two organisms live in close association with each otherassociation with each other– parasitism, mutualism, commensalism parasitism, mutualism, commensalism

are examplesare examples

SymbiosisSymbiosis

mostly used to describe situations in mostly used to describe situations in which at least one species benefitswhich at least one species benefits

Over time, species in a close relationship Over time, species in a close relationship may may coevolvecoevolve – meaning they develop – meaning they develop adaptations that reduce the harm or adaptations that reduce the harm or improve the benefit of the relationshipimprove the benefit of the relationship

-coevolution is seen in the -coevolution is seen in the relationships of flowering plants and relationships of flowering plants and their pollinatorstheir pollinators

Graphic OrganizerGraphic Organizer