Chapter 5Population Ecology

Populations Growth

Population Growth Three factors can affect population size:

number of birthsthe number of deathsthe number of individuals that enter

or leave the population. * Simply put, a population will increase or

decrease in size depending on how many individuals are added to it or removed from it

Immigration & EmmigrationImmigration

the movement of individuals into an area, is another factor that can cause a population to grow.

Emigration the movement of individuals out of an area, can cause a population to decrease in size.

In 1911, 25 reindeer were introduced on Saint Paul Island in the Pribolofs off Alaska. The population grew rapidly and nearly exponentially until about 1938, when there were over 2000 animals on the 41-square-mile island. The reindeer badly overgrazed their food supply (primarily lichens) and the population “crashed.” Only eight animals could be found in 1950. A similar sequence of events occurred on Saint Matthew Island from 1944 through 1966. [After Krebs (1972) after V. B. Scheffer (1951). The Rise and Fall of a Reindeer Herd. Science 73: 356–362.]

Exponential GrowthPopulations growing without restriction!

If a population has abundant space and food, and is protected from predators and disease, then organisms in that population will multiply and the population size will increase.

Exponential Growth

Exponential growth occurs when the individuals in a population reproduce at a constant rate. Under ideal conditions with unlimited resources, a population will grow exponentially.

Exponential population growth is described by the simple differential equation dN/dt = rNwhere,change in number of individuals (dN) per Change in time (dt) = growth rate (rN) 

Logistic GrowthLogistic growth occurs when a

population's growth slows or stops following a period of exponential growth.

  As resources become less

available, the growth of a population slows or stops. The general, S-shaped curve of this growth pattern, called logistic growth

Carrying Capacity The number or the largest number of individuals that a given environment can support.

Variations of the Logistic ModelIf food becomes scarce, the population

will experience an overshoot by becoming larger than the spring carrying capacity and will result in a die-off, or population crash.

environmental resistance. : the sum of the environmental factors (such as drought, mineral deficiencies, and competition) that tend to restrict the biotic potential of an organism

Population-same species, same place, same time

Characteristics of PopulationsThree important characteristics of a population

•geographic distribution•Density•growth rate

Geographic distribution, or range, is a term that

describes the area inhabited by a

population.

Clumped- Most commonsocial, protection, resources

Uniform- predator-territorialityAllelopathy

Random- less commonResources evenly distributed

Population Density Population density is the number of individuals per unit area

. The population

of saguaro cactus in the desert plant community has a low density, whereas other plants in that community have a relatively high density.

Factors that Restrict the Size of a Population

Limiting Factors of Environmental Resistance

Density-Dependent Limiting Factors

1. The degree of influence depends on the size of the population.

2. Examples: competition, predation, parasitism, stress caused by crowding, disease

3. Seldom totally eliminate a population

4. Some populations are self-controlling in that they have mechanisms to reduce competition – delayed maturation caused by malnutrition, migration, cannibalism.

Density-Independent Limiting Factors

1. The degree of influence is not related to population size.

2. Examples: pollution, habitat destruction, natural disasters, weather

3. Usually just reduce the population below the cc. but they have the ability to totally eliminate a population

Density Independent Factors Influencing Populations

Density Dependent Factors Influencing Populations

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Types of SpeciesGeneralist

large nichestolerate wide range of environmental variationsdo better during changing environmental

conditions

Specialistnarrow niches more likely to become endangered do better under consistent environmental

conditions

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Depending upon the characteristics of the organism, organisms will follow a biotic potential or carrying capacity type reproductive strategy

The r-strategists (Type III)1. High biotic potential – reproduce very fast2. Are adapted to live in a variable climate3. Produce many small, quickly maturing offspring = early

reproductive maturity4. “Opportunistic” organismsThe K-strategists (Type I)1. Adaptations allow them to maintain population values

around the carrying capacity2. They live long lives3. Reproduce late4. Produce few, large, offspring

r and k strategists

Survivorship Curves

Survivorship curves show the distribution of individuals in a population according to age

Humans and most mammals have a Type I survivorship curve because death primarily occurs in the older years.

Birds have a Type II survivorship curve, as death at any age is equally probable.

Trees have a Type III survivorship curve because very few survive the younger years, but after a certain age, individuals are much more likely to survive.

/

r-strategist

k-strategist

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Community Relationships

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Types of Species

Native speciesNative species normally live and thrive in a particular ecosystem

Nonnative speciesNonnative species are introduced - can be called exotic or alien

Indicator speciesIndicator species serve as early warnings of danger to ecosystem- birds & amphibians

Keystone speciesKeystone species are considered of most importance in maintaining their ecosystem

Identify some of the factors that could cause a change in the number of red crabs onChristmas Island. Predict what would happen to the red crab population as the result of a (1) drought, a (2) hurricane, or the introduction of a (3)predator to the ecosystem.

Christmas Island red crab Gecarcoidea natalis

The land crab that is endemic to Christmas Island in the Indian Ocean. An estimated that 43.7 million adult red crabs lived on Christmas Island alone. The accidental introduction of the yellow crazy ant is believed to have killed about 10–15 million of these in recent years.

Christmas Island red crabs are well known for their annual mass migration to the sea to lay their eggs in the ocean.

Christmas Island Land CrabKeystone Species

Christmas Island's biodiversity - land crabs are a keystone species in the forest ecology: they dig burrows, turn over the soil, and fertilise it with their droppings.

Seedlings that were previously eaten by crabs started to grow and, as a result, changed the structure of the forest.

Weeds also spread into the rainforest because there are no crabs to control them.

Factors that Influence Population Size

Density-dependent factors- the size of the population will influence an individual’s probability of survival.

Density-independent factors- the size of the population has no effect on the individual’s probability of survival.

Exponential Growth Model

Intrinsic growth rate- under ideal conditions, with unlimited resources, the maximum potential for growth.

Resource Patitioning

Predation

Predation- the use of one species as a resource by another species.

True predators- kill their prey.Herbivores- consume plants as prey.Parasites- live on or in the organism they

consume.Parasitoids- lay eggs inside other

organisms.

Mutualism

Mutualism- A type of interspecific interaction where both species benefit.

CommensalismCommensalism- a type of relationship

in which one species benefits but the other is neither harmed nor helped.

Community Ecology

Each species has a particular ecological niche or role that it plays in an ecosystem.

Competitive Exclusion Principle

Two species that have exactly the same requirements cannot coexist in exactly the same habitat.

r-Selected Species

Cockroach Dandelion

Many small offspring

Little or no parental care and protection of offspring

Early reproductive age

Most offspring die before reaching reproductive age

Small adults

Adapted to unstable climate and environmental conditions

High population growth rate (r)

Population size fluctuates wildly above and below carrying capacity (K)

Generalist niche

Low ability to compete

Early successional species

Fewer, larger offspring

High parental care and protection of offspring

Later reproductive age

Most offspring survive to reproductive age

Larger adults

Adapted to stable climate and environmental conditions

Lower population growth rate (r)

Population size fairly stable and usually close tocarrying capacity (K)

Specialist niche

High ability to compete

Late successional species

ElephantSaguaro

K-Selected Species

The Giant Panda: Specialized and Endangered

Classic k-strategist = specialist

Feeds exclusively on bamboo (1/3 of body weight)

Habitat fragmentation has created “habitat islands” of bamboo in southwestern China due to human encroachment.

12 protected reserves in China.

Why Are Panda Faced With Extinction?

Illegal poaching (pelt brings in $40,000-60,000).Only one cub per female survives each year.Gestation period = 22 monthsPicky about mates. Find each other through

scent, become isolated due to habitat fragmentation.

Habitat islands interrupt natural migration to adjacent areas when bamboo population crashes in local areas.

Approximately 700 panda left between zoos and the wild.

What Are Indicator Species?

Indicator species serve as early warnings of damage to a community.

Birds and butterflies are migratory and are excellent indicators of the environment. They do not return to areas along their migratory routes where deforestation has occurred or where broad spectrum pesticides have been applied.

Amphibians are also a universal indicator of environmental degradation as they respire through their skin.

Indicator Species

As indicator species, amphibians may be sending us an important message about the health of the global environment.

They don’t need us, but we and other species need them.

Golden toads – once prevalent in Costa Rica’s cloud forest have disappeared.

Indicator Species in New England

Why are species in trouble

HIPPCO

What Are Keystone Species?

A keystone species holds a community together, when it disappears, so does the biological community. Elimination of a keystone species dramatically alters the structure and function of a community.

American Alligator – a Keystone Species Largest North

American reptile; only humans are their predator.

Hunted nearly to extinction for exotic meat, and leather to make shoes and pocketbooks, and for sport.

Ecological Niche of American Alligator

Dig gator holes that collect freshwater during the dry season which serve as refuges for aquatic life, and supply freshwater and food for many animals.

Ecological Niche of American AlligatorAlligator nesting mounds serve as nesting

and feeding sites for herons and egrets

Ecological Niche of American AlligatorAlligator eat large numbers of predatory

gar fish and help maintain healthy numbers of game fish such as bass and bream.

Ecological Niche of American AlligatorAs alligators

move from gator holes to nesting sites, they keep areas of open water free of invading vegetation. This helps to maintain healthy ecosystems with flowing water.

American Alligator Protection

In 1967, the US Government placed the American alligator on the Endangered Species List, which protected it from hunting.

By 1975, the American alligator populations rebounded successfully.

Keystone Species Youtube series

E.O. Wilson

“The loss of a keystone species is like a drill accidentally striking a power line. It causes lights to go out all over”

Interaction between SpeciesChapter 5Competition

The outcome is negative for both groups

SymbiosisBenefits both participants

Predation and parasitismThe outcome benefits one and is detrimental to

the other.

Symbiosis

Describes a relationship between two organisms beneficial to both enhances each organism’s

chance of persistingEach partner called a

symbiontE.g. reindeer and bacteria

in the gut The result is food for

reindeer, home for bacteria

Recall- endosymbiont theory

Amazing Adaptations

Parasitism

Mutualism and Commensalism

Predation and ParasitismRelationship is beneficial for predator or parasite and

negative for prey or host.Predation- One organism (predator) feeds on other live

organisms (prey).

Parasitism- One organism (the parasite) lives on, in, or within another (the host).

North Woods Ecosystem Population Fluctuations

exponential

r-species

K-species

--------------------------------------------------Carrying Capacity

The Food Web of the Harp Seal

Food webs are complex because most species feed on several trophic levels.

Harp seal (shown at 5th level)Feeds on flatfish (4th level)But also feed on foods from 2nd – 4th A species that feeds on several levels placed in

a category one above the highest level it feeds on.

Community Level InteractionsSea Otter Manages Kelp ForestIndirect and more complicated community wide

affects species have on one another.Sea otter of the Pacific Ocean

Came close to extinction because of over hunting for fur

Feed on shellfish (abalone, sea urchins)Where sea otters abundant kelp beds abundant and

few sea urchins Otters affects the abundance of kelp

Sea otters have community level effectWhere more kelp is present more habitat for

many speciesKeystone species

A species that has a large effect on its community or ecosystem

Holistic viewEcological community is more than the sum

of its parts

Community Level Interactions

Lead into Chapter 12 Food

ROOST

Crash landing

Hindfeet

The Evolution of Life on Earth

MammalsMore capable brain

and faster metabolismPlacental uterus one

key to mammalian success

Interaction between SpeciesChapter 5Competition

The outcome is negative for both groups

SymbiosisBenefits both participants

Predation and parasitismThe outcome benefits one and is detrimental to

the other.

Symbiosis

Describes a relationship between two organisms beneficial to both enhances each organism’s

chance of persistingEach partner called a

symbiontE.g. reindeer and bacteria

in the gut The result is food for

reindeer, home for bacteria

Recall- endosymbiont theory

Amazing Adaptations

Parasitism

Mutualism

Commensalism

Amazonian Rain Forest Brazil The First Agriculture 60mya –Symbiosis

Extincitions

Polar Bear and Global Warming

Amazing Diversity of Organisms & Sea Dragons

Competitive Exclusion Principle

Two species that have exactly the same requirements cannot coexist in exactly the same habitat.

Predation and ParasitismRelationship is beneficial for predator or parasite and

negative for prey or host.Predation- One organism (predator) feeds on other live

organisms (prey).

Parasitism- One organism (the parasite) lives on, in, or within another (the host).

North Woods Ecosystem Population Fluctuations

exponential

r-species

K-species

--------------------------------------------------Carrying Capacity

The Food Web of the Harp Seal

Food webs are complex because most species feed on several trophic levels.

Harp seal (shown at 5th level)Feeds on flatfish (4th level)But also feed on foods from 2nd – 4th A species that feeds on several levels placed in

a category one above the highest level it feeds on.

Community Level InteractionsSea Otter Manages Kelp ForestIndirect and more complicated community wide

affects species have on one another.Sea otter of the Pacific Ocean

Came close to extinction because of over hunting for fur

Feed on shellfish (abalone, sea urchins)Where sea otters abundant kelp beds abundant and

few sea urchins Otters affects the abundance of kelp

Sea otters have community level effectWhere more kelp is present more habitat for

many speciesKeystone species

A species that has a large effect on its community or ecosystem

Holistic viewEcological community is more than the sum

of its parts

Community Level Interactions

Lead into Chapter 12 Food

ROOST

Crash landing

Hindfeet

Fossil Record

Most of what we know of the history of life on earth comes from fossils (SJ Gould)

Give us physical evidence of organismsShow us internal structure

Uneven and incomplete record of speciesWe have fossils for 1% of species believed to have lived

on earthSome organisms left no fossils, others decomposed,

others have yet to be found. Other info from ancient rocks, ice core, DNA The whale as an example Other evidence here

Speciation

Adapted to heatthrough lightweightfur and long ears, legs, and nose, whichgive off more heat.

Adapted to coldthrough heavierfur, short ears,short legs, shortnose. White furmatches snowfor camouflage.

Gray Fox

Arctic Fox

Different environmentalconditions lead to differentselective pressures and evolutioninto two different species.

Spreadsnorthwardandsouthwardandseparates

Southernpopulation

Northernpopulation

Early foxpopulation

Speciation

Two species arise from one Requires Reproductive isolation

Geographic: Physically separatedTemporal: Mate at different timesBehavioral: Bird calls / mating ritualsAnatomical: Picture a mouse and an elephant hooking upGenetic Inviability: Mules

Allopatric Speciation that occurs when 2 or more populations of a species are

geographically isolated from one another The allele frequencies in these populations change Members become so different that that can no no longer interbreed See animation

Sympatric Populations evolve with overlapping ranges Behavioral barrier or hybridization or polyploidy

TAKE HOME #2

Macroevolution is the cumulative result of a series of microevolutionary eventsTypically seen in fossil recordNobody around to see the small, gene pool

changes over time.

COEVOLUTION: Interaction Biodiversity

Species so tightly connected, that the evolutionary history of one affects the other and vice versa.Ant Farmers of the Amazon

Coevolution

Interactions between species can cause microevolutionChanges in the gene pool of one species can cause changes

in the gene pool of the otherAdaptation follows adaptation in something of a long

term “arms race” between interacting populations of different populationsThe Red Queen Effect

Can also be symbiotic coevolutionAngiosperms and insects (pollinators)Corals and zooxanthellae Rhizobium bacteria and legume root nodules

And NUH is the letter I use to spell Nutches,Who live in small caves, known as Niches, for hutches.These Nutches have troubles, the biggest of which isThe fact there are many more Nutches than Niches.Each Nutch in a Nich knows that some other NutchWould like to move into his Nich very much.So each Nutch in a Nich has to watch that small NichOr Nutches who haven't got Niches will snitch.

-On Beyond Zebra (1955)

Dr. Seuss

Niches

A species functional role in an ecosystem Involves everything that affects its survival and reproduction

Includes range of tolerance of all abiotic factors Trophic characteristics How it interacts with biotic and abiotic factors Role it plays in energy flow and matter cycling

Fundamental Niche Full potential range of physical chemical and biological conditions

and resources it could theoretically use if there was no direct competition from other species

Realized Niche Part of its niche actually occupied

Generalist vs. Specialist Lives many different places, eat many foods, tolerate a wide range

of conditions vs few, few, intolerant… Which strategy is better in a stable environment vs unstable?

POLLENPEEPERS

POLLENPEEPER EVOLUTION

Niche Overlap

Region of niche overlap

Generalist specieswith a broad nicheGeneralist species

with a narrow nicheNiche

breadth

Nicheseparation

Num

ber

of in

divi

dual

s

Resource use

Competition Shrinks Niches

Competition and Community Diversity

•Species evolve to minimize competition and niche overlap

•Results in a diverse matrix of differing species within a community

What’s This Niche Stuff Got to do with Evolution and Biodiversity?

Hmmmmm….Let’s think about three key points….

The more niches you have in an ecosystem…The more of a generalist species you are…The more of a specialist species you are…

Ordovician: 50% of animal families,

Devonian: 30% of animal families,

Permian: 90% of animal families, including over 95% of marine species; many trees, amphibians, most bryozoans and brachiopods, all trilobites.

Triassic: 35% of animal families, including many reptiles and marine mollusks.

Cretaceous: up to 80% of ruling reptiles (dinosaurs); many marine species including manyforaminiferans and mollusks.

Current extinction crisis causedby human activities.

Species and families experiencing mass extinction

Bar width represents relative number of living species

Extinction

Millions ofyears ago

PeriodEra

Pal

eozo

icM

eso

zoic

Cen

ozo

ic Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

Today

65

180

250

345

500Extinction

Extinction

Extinction

Extinction

Extinction

Extinction

Local, ecological and true extinction The ultimate fate of all species just as death is for all individual

organisms 99.9% of all the species that have ever existed are now extinct

To a very close approximation, all species are extinct Background vs. Mass Extinction

Low rate vs. 25-90% of total Five great mass extinctions in which numerous new species

(including mammals) evolved to fill new or vacated niches in changed environments

10 million years or more for adaptive radiations to rebuild biological diversity following a mass extinction

Extinctions open up new opportunities for speciation and adaptive radiation..BUT you can have too much of a good thing!

Factors Affecting Extinction Rates

Natural Extinctions Climate change Cataclysmic event (volcano, earthquake)

Human Activities Habitat Loss/Fragmentation Introduction of exotic/invasive species Pollution Commercial harvesting Accidental killing (tuna nets) Harassing Pet Trade Urbanization Damming/Flooding Agricultural conversion

Extinction in the Context of Evolution

If the environment changes rapidly andThe species living in these environments do not

already possess genes which enable survival in the face of such change and

Random mutations do not accumulate quickly enough then,

All members of the unlucky species may die

BiodiversitySpeciation – Extinction=BiodiversityHumans major force in the premature extinction of species.

Extinction rate increased by 100-1000 times the natural background rate.

As we grow in population over next 50 years, we are expected to take over more of the earth’s surface and productivity. This may cause the premature extinction of up to a QUARTER of the earth’s current species and constitute a SIXTH mass extinction Genetic engineering won’t solve this problem Only takes existing genes and moves them around

Know why this is so important and what we are losing as it disappears….

USING EVOLUTION AND GENETICS TO INFORM CONSERVATIONEcoRegions Approach

Identifying biodiversity “hotspots” and focusing conservation efforts on maintaining those ecosystems

Ex. Tropics, Appalachian Mountains, etc.“Umbrella Species” Conservation

Conserve one “sexy”, species and you conserve several others because if the interactions they have with one another

Keystone species conceptSpecies Survival Plan (SSP)

Zoo captive breeding programs Population genetics in wild populations

Ex. Cheetahs, Primates, Bears, etc.

Federal and International Legislation

Endangered Species Act (1973)Protection for endangered and threatened plant and

animal species & their habitatsEffectiveness??? Exemptions are often granted if

• No alternatives to the project

• National or regional significance of project

• Benefits outweigh those of any alternatives

CITES (late 1970s)-prohibits trade and commerce of threatened and endangered speciesBy 1998: signed by 144 countries

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Niche isthe species’ occupation

and its

Habitat location of species

(its address)

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Niche

A species’ functional role in its ecosystem; includes anything affecting species survival and reproduction

1.Range of tolerance for various physical and chemical conditions

2.Types of resources used

3.Interactions with living and nonliving components of ecosystems

4.Role played in flow of energy and matter cycling

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Niche

Realized niche:Realized niche: more more restricted set of conditions restricted set of conditions under which the species under which the species actually exists due to actually exists due to interactions with other interactions with other speciesspecies

Fundamental niche:Fundamental niche: set of set of conditions under which a conditions under which a species might exist in the species might exist in the absence of interactions with absence of interactions with other speciesother species

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Biodiversity

Biodiversity increases with speciationdecreases with extinction

Give-and-take between speciation and extinction changes in biodiversity

Extinction creates evolutionary opportunities for adaptive radiation of surviving species

Coevolution

Evolutionary changeEvolutionary changeOne species acts as a selective force on One species acts as a selective force on

a second speciesa second species Inducing adaptations Inducing adaptations that act as selective force on the first that act as selective force on the first

speciesspecies Example:Example:1.1. Wolf and MooseWolf and Moose2.2. Acacia ants and Acacia treesAcacia ants and Acacia trees2.2. Yucca Plants and Yucca mothsYucca Plants and Yucca moths3.3. LichenLichen

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Extinction

Background extinctionBackground extinction - species disappear - species disappear at a low rate as local conditions changeat a low rate as local conditions change

Mass extinctionMass extinction - catastrophic, wide-spread - catastrophic, wide-spread events --> abrupt increase in extinction rateevents --> abrupt increase in extinction rate

Five mass extinctions in past 500 million Five mass extinctions in past 500 million yearsyears

Adaptive radiationAdaptive radiation - new species evolve - new species evolve during recovery period following mass during recovery period following mass extinction extinction

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How do species move?Humans (accidental and intended)Animals (sticky seeds and scat)Wind and ocean currents (+ or -)Land bridgesStepping stone islands

affected by climactic changes (glaciation)ocean levelsshort-term weather patterns

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Nonnative Nonnative SpeciesSpecies

Nonnative plant species are invading the Nonnative plant species are invading the nation's parks at an alarming rate, nation's parks at an alarming rate, displacing native vegetation and displacing native vegetation and threatening the wildlife that depend on threatening the wildlife that depend on themthem

At some, such as Sleeping Bear Dunes At some, such as Sleeping Bear Dunes National Lakeshore in Michigan, as much National Lakeshore in Michigan, as much as 23 percent of the ground is covered as 23 percent of the ground is covered with alien species, and the rate of with alien species, and the rate of expansion is increasing dramatically.expansion is increasing dramatically.

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Indicator Species

a species whose status provides information on the overall condition of the ecosystem and of other species in that ecosystem

reflect the quality and changes in environmental conditions as well as aspects of community composition

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Keystone Species

A keystone is the stone at the top of an arch that supports the other stones and keeps the whole arch from falling a species on which the persistence of a large number of other

species in the ecosystem depends.

If a keystone species is removed from a system the species it supported will also disappear other dependent species will also disappear

Examples top carnivores that keep prey in check large herbivores that shape the habitat in which other species live important plants that support particular insect species that are prey

for birds bats that disperse the seeds of plants

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Species Interaction

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CompetitionAny interaction between two or more species for a resource that causes a decrease in the population growth or

distribution of one of the species1. Resource competition

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Competition

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Resource Competition

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CompetitionAny interaction between two or more species for a resource that causes a decrease in the population growth or

distribution of one of the species1. Resource competition

2. Preemptive competition

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CompetitionAny interaction between two or more species for a resource that causes a decrease in the population growth or

distribution of one of the species1. Resource competition

2. Preemptive competition

3. Competitive exclusion

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Competitive ExclusionCompetitive Exclusion

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CompetitionAny interaction between two or more species for a resource that causes a decrease in the population growth or

distribution of one of the species1. Resource competition2. Preemptive competition3. Competition exploitation 4. Interference competition

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Competition

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PREDATION

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Predator AdaptationsPrey detection and recognition

sensory adaptationsdistinguish prey from non-prey

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Predator AdaptationsPrey detection and recognition

sensory adaptationsdistinguish prey from non-prey

Prey capturepassive vs. activeindividuals vs. cooperative

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Predator AdaptationsPrey detection and recognition

sensory adaptationsdistinguish prey from non-prey

Prey capturepassive vs. activeindividuals vs. cooperative

Eating preyteeth, claws etc.

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145

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Prey AdaptationsAvoid detection

camouflage, mimics, diurnal/nocturnal

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Prey AdaptationsAvoid detection

camouflage, mimics, diurnal/nocturnal

Avoid capturefleeresistescape

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Prey AdaptationsAvoid detection

camouflage, mimics, diurnal/nocturnal

Avoid capturefleeresistescape

Disrupt handling (prevent being eaten)struggle?protection, toxins

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HerbivoryHerbivore needs to find most nutritious

circumvent plant defenses

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HerbivoryHerbivore needs to find most nutritious

circumvent plant defenses

Herbivory strong selective pressure on plantsstructural adaptations for defensechemical adaptations for defense

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Herbivory

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Herbivory

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Herbivory

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Symbiosis: Mutualists,

Commensalists and

Parasites

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Symbiosis and symbiotic relationship are two commonly misused terms

Translation of symbiosis from the Greek literally means “living together”

Both positive and negative interactions

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MutualismDEFINITION:

An interaction between two individuals of different species that benefits both partners in this interaction

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Yucca’s only pollinator is the yucca moth. Hence entirely dependent on it for dispersal.

Yucca moth caterpillar’s only food is yucca seeds.

Yucca moth lives in yucca and receives shelter from plant.

Yucca and Yucca Moth

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Lichen (Fungi-Algae)Symbiotic relationship of algae

and fungae…results in very different growth formas with and without symbiont.

What are the benefits to the fungus?

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CommensalistsBenefit from the

host at almost no cost to the host

Eyelash mite and humans

Us and starlings or house sparrows

Sharks and remora

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Parasites and ParasitoidsParasites: draw resources from host

without killing the host (at least in the short term).

Parasitoids: draw resources from the host and kill them swiftly (though not necessarily consuming them).

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Parasitic wasps

Important parasites of larvae.

In terms of biological control, how would this differ from predation?

ovipositor

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Ecological Processes

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Ecological SuccessionEcological Succession

Primary and Secondary SuccessionPrimary and Secondary Succession

gradual & fairly predictable change in species composition with time

•some species colonize & become more abundant;

•other species decline or even disappear.

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Ecological SuccessionEcological SuccessionGradual changing environment in

favor of new / different species / communities

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Primary Primary SuccessionSuccession

Glacier Glacier RetreatRetreat

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