evolution, biodiversity, and community processes

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Evolution, Evolution, Biodiversity, and Biodiversity, and

Community Community Processes Processes

Chapter 8Chapter 8

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BiodiversityBiodiversity

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How do we get How do we get Biodiversity?Biodiversity?

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BiodiversityBiodiversity• Biodiversity

– increases with speciation– decreases with extinction

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

• Extinction creates evolutionary opportunities for adaptive radiation of surviving species

Interpretations of SpeciationInterpretations of Speciation

Two theories:Two theories:1.1. Gradualist Model (Neo-Gradualist Model (Neo-

Darwinian):Darwinian):

Slow changes in species Slow changes in species overtimeovertime

2.2. Punctuated Equilibrium:Punctuated Equilibrium:

Evolution occurs in spurts of Evolution occurs in spurts of relatively rapid changerelatively rapid change

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Adaptive Adaptive RadiationRadiation

Emergence of Emergence of numerous species numerous species from a common from a common ancestor introduced ancestor introduced to new and diverse to new and diverse environmentsenvironmentsExample::Hawaiian Hawaiian Honeycreepers Honeycreepers

Convergent EvolutionConvergent Evolution

Species from different evolutionary Species from different evolutionary branches may come to resemble one branches may come to resemble one another if they live in very similar another if they live in very similar

environmentsenvironments

Example:Example:

1. Ostrich (Africa) and Emu (Australia).1. Ostrich (Africa) and Emu (Australia).

2. Sidewinder (Mojave Desert) and2. Sidewinder (Mojave Desert) and

Horned Viper (Middle East Desert)Horned Viper (Middle East Desert)

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CoevolutionCoevolution• Evolutionary changeEvolutionary change

– One species acts as a selective force on a One species acts as a selective force on a second speciessecond 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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ExtinctionExtinction• Extinction of a species occurs when it

ceases to exist; may follow environmental change - if the species does not evolve

• Evolution and extinction are affected by:– large scale movements of continents– gradual climate changes due to continental

drift or orbit changes– rapid climate changes due to catastrophic

events

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ExtinctionExtinction• 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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Mass ExtinctionsMass ExtinctionsDate of the Extinction

Event

Percent

Species Lost

Species Affected

65 mya

(million

years ago)

85 Dinosaurs, plants (except ferns and seed bearing plants), marine

vertebrates and invertebrates. Most mammals, birds, turtles, crocodiles,

lizards, snakes, and amphibians were unaffected.

213 mya 44 Marine vertebrates and invertebrates

248 mya 75-95 Marine vertebrates and invertebrates

380 mya 70 Marine invertebrates

450 mya 50 Marine invertebrates

http://www.geog.ouc.bc.ca/physgeog/contents/9h.html

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1. Diversity is a balance of factors that increase diversity and factors that decrease diversity

2. Production of new species (speciation), and influx can increase diversity

3. Competitive exclusion, efficient predators, catastrophic events (extinction) can decrease diversity

4. Physical conditions a. variety of resourcesb. Predatorsc. environmental variability

Equilibrium Theory of BiodiversityEquilibrium Theory of Biodiversity

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• Richness (number of species)

• Relative abundance

• How do we describe these differences?

Comparison of Two Comparison of Two CommunitiesCommunities

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Biogeographical ChangesBiogeographical Changes

• Richness declines from equator to pole

• Due to:

–Evolutionary history

–ClimateFig 53.23 Bird species numbers

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• Species-area curve

• The larger the geographic area, the greaterthe numberof species

Geographic (Sample) SizeGeographic (Sample) Size

Fig. 23.25 North American Birds

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Species Richness on IslandsSpecies Richness on Islands• Depends on:Depends on:

–Rate of immigration to islandRate of immigration to island–Rate of extinction on islandRate of extinction on island

• These in turn depend on:These in turn depend on:–Island sizeIsland size–Distance from mainlandDistance from mainland

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

– affected by climactic changes (glaciation)– ocean levels– short-term weather patterns

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What allowed colonization?What allowed colonization?

• Niche opening

• No competition

• Endemics not utilizing resources

• Accessibility to colonists

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Theory of Island BiogeographyTheory of Island Biogeography

1. Immigration rate decreases as island diversity increases

2. Extinction increases as island diversity increases

3. Species equilibrium on islands is a balance of immigration and local extinction

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1.Smaller islands have lower total populations

2.Probability of extinction increases with lower population

3.Smaller islands have lower species diversity

Theory of Island BiogeographyTheory of Island Biogeography

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1.Islands further from mainland have lower immigration rates

2.More distant islands have lower species diversity

Theory of Island BiogeographyTheory of Island Biogeography

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Community Community RelationshipsRelationships

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Niche isthe species’ occupation

and its

Habitat location of species

(its address)

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NicheNicheA 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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NicheNiche

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

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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Types of SpeciesTypes of Species•Generalist

–large niches–tolerate wide range of environmental variations–do better during changing environmental

conditions

•Specialist–narrow 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-strategists1. 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-strategists1. Adaptations allow them to maintain population values around the

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

r and k strategistsr and k strategists

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Types of SpeciesTypes 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

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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 with as 23 percent of the ground is covered with alien species, and the rate of expansion is alien species, and the rate of expansion is increasing dramatically.increasing dramatically.

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Indicator Indicator SpeciesSpecies

• 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 SpeciesKeystone 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 Species InteractionInteraction

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CompetitionCompetitionAny 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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Resource CompetitionResource Competition

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Competitive ExclusionCompetitive Exclusion

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PREDATION

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Predator AdaptationsPredator Adaptations• Prey detection and recognition

–sensory adaptations–distinguish prey from non-prey

• Prey capture–passive vs. active–individuals vs. cooperative

• Eating prey–teeth, claws etc.

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Prey AdaptationsPrey Adaptations• Avoid detection

– camouflage, mimics, – diurnal/nocturnal

• Avoid capture– flee– resist– escape

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

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HerbivoryHerbivoryHerbivore needs to find most

nutritious–circumvent plant defenses

Herbivory strong selective pressure on plants–structural adaptations for defense–chemical adaptations for defense

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Symbiosis: Symbiosis: Mutualists, Mutualists,

Commensalists Commensalists and Parasitesand 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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MutualismMutualismDEFINITION:

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

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MutualismMutualism

• Increase birth rates

• Decrease death rates

• Increase equilibrium population densities,

Raise the carrying capacity

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PollinationPollination

• Animals visit flowers to collect nectar and incidentally carry pollen from one flower to another

• Animals get food and the plant get a pollination service

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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 Yucca and Yucca Moth

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Lichen (Fungi-Algae)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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Nitrogen FixationNitrogen Fixation

Darkest areas are nuclei, the mid-tone areas are millions of bacteria Gram -, ciliate

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Obligatory MutualismObligatory Mutualism• Obligatory: An organism can't live

without the mutualism--either cannot survive or cannot reproduce. – the common pollinator systems like

bees and flowering plants– protozoans in the guts of termites– the alga in the lichen partnership

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Facultative MutualismFacultative Mutualism• Facultative: This is "take it or leave

it" for one or both partners• While the organism benefits when

the mutualism is present, it can still survive and reproduce without it– ant mutualisms, such as ants protecting

plants from predation – ants tending aphids

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CommensalistsCommensalists• Benefit 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 and Parasitoids• Parasites: 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 waspsParasitic wasps

• Important parasites of larvae.

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

ovipositor

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Ecological Ecological ProcessesProcesses

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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 SuccessionPrimary Succession

•Gradual establishment of biotic communities in an area where no life existed before

•No preexisting seed bank•newly formed islands (i.e. volcanic origin)

•retreat of a glacier

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Primary Primary SuccessionSuccession

Glacier Glacier RetreatRetreat

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Secondary SuccessionSecondary Succession• Gradual reestablishment of biotic communities in an area where one was previously present.

• Preexisting seed bank

•treefall gaps

•"old field succession"

•forest fire

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DisturbanceDisturbanceEvent that disrupts an ecosystem or community;

• Natural disturbance

•tree falls, fires, hurricanes, tornadoes, droughts, & floods

• Human–caused disturbance

•deforestation, erosion, overgrazing, plowing, pollution,mining

• Disturbance can initiate primary and/or secondary succession

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Ecological StabilityEcological StabilityCarrying Capacity – maximum number of

individuals the environment can support

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Ecological Stability - StressEcological Stability - Stress1. Drop in Primary Productivity2. Increased Nutrient Losses3. Decline or extinction of indicator

species4. Increased populations of insect

pests or disease organisms5. Decline in Species diversity6. Presence of Contaminants