Ch. 3 - Evolution, Biodiversity, and Central Case Study ... · PDF...

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© 2012 Pearson Education, Inc.

Ch. 3 - Evolution, Biodiversity, andPopulation Ecology:• Natural selection• How evolution

influencesbiodiversity

• Reasons for speciesextinction

• Ecologicalorganization

• Populationcharacteristics

• Population ecology© 2012 Pearson Education, Inc.

Central Case Study: Striking Gold in a CostaRican Cloud Forest

• Golden toads were discovered in Monteverde,Costa Rica in 1964– 200 males in a 16-ft. area

• The mountainous cloud forestwas ideal for amphibians

• The toads vanished from Earthwithin 25 years– Climate change caused the

forest to dry out– A fungus also killed them


Evolution is the wellspring of biodiversity

• Species: a population or group of populations …– Whose members share characteristics and ….– Can breed with each other to produce fertile offspring

• Population: a group of individuals of a species that livein the same area

• Evolution: means change over time– Biological evolution: genetic change in populations over

time


Natural selection

• Evolution may be random– Or directed by natural selection

• Natural selection: The process whereby inheritedcharacteristics that enhance survival and reproduction …

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Species adapt to the environment

• A parent that produces more offspring passes on moregenes to future generations

• Over time, characteristics (traits) that lead to betterreproductive success become more prevalent

• Adaptive trait (adaptation): a trait that promotesreproductive success

• Sexual reproduction also leads to genetic variation– Producing new combinations of genes

• Environmental conditions determine the pressures ofnatural selection


Natural selection leads to biodiversity

• It also helps elaborate anddiversify traits– Which leads to the

formation of new species

• Natural selection weeds outunfit individuals


Evidence of natural selection is everywhere

• It is evident in every adaptation of every organism• Artificial selection: the process of selection conducted

under human direction– Producing the great diversity of dog breeds and crops


Evolution generates biological diversity

• Biological diversity (biodiversity): the variety of lifeacross all levels of biological organization– Species– Genes– Populations– Communities

• Scientists have described 1.8 million species– Up to 100 million species may exist– Tropical rainforests are rich in biodiversity

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Speciation produces new types of organisms

• The process of generating newspecies from a single species

• Allopatric speciation: speciesform as a result of physicalseparation of populations– The main mode of speciation– Populations can be separated by

glaciers, rivers, mountains– Each population, with its own

set of mutations, diverges


Speciation results in diverse life forms

• How do major groups diverge over time?• Phylogenetic trees: branching diagrams show

relationships among species, groups, genes, etc.– Represent life’s history


Fossils also show life’s history

• Fossil: an imprint in stone of a dead organism• Fossil record: the cumulative body of fossils worldwide• Phylogenetic trees and the fossil record show:

– Life has existed on Earth for 3.5 billion years– Life evolved complex structures from simple ones– Life evolved large sizes from small ones– But natural selection can also favor simplicity and small

size


Extinction

• Most species that once lived arenow gone

• Extinction: the disappearance ofa species from Earth– Species last 1–10 million years

• Biological diversity is now beinglost at an astounding rate– This loss of species is irreversible

Number of species = speciation – extinction

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Some species are vulnerable to extinction

• Extinction occurs when the environment changes rapidly– Natural selection can’t keep up, so species can’t adapt

• Many factors cause extinction:– Climate change, changing sea levels, severe weather– Arrival of new species, small populations– Specialized species

• Endemic species: exists only in a certain, specializedarea– Very susceptible to extinction– These species usually have small populations


Earth has had several mass extinctions

• Background extinction rate: extinction usually occursslowly, one species at a time

• Mass extinction events: killed off massive numbers ofspecies at once– Occurred five times in Earth’s history– 50–95% of all species went extinct at one time

• Cretaceous-Tertiary (K-T) event: 65 million years ago– A gigantic asteroid caused dinosaur extinction

• End-Permian event: 250 million years ago– 75–95% of species went extinct from unknown causes


We study ecology at several levels

• Ecology: studies interactionsamong organisms– And their environment

• Biosphere: the total livingthings on Earth– And the areas they inhabit


Levels of ecological studies

• Population ecology: investigates population changes– The distribution and abundance of individuals– Why some populations increase and others decrease

• Community ecology: focuses on patterns of speciesdiversity and interactions

• Ecosystem ecology studies living and nonlivingcomponents of systems to reveal patterns– Nutrient and energy flows

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Each organism has habitat needs

• Habitat: the environment where an organism lives– It includes living and nonliving elements

• Habitat use: nonrandom patterns where organisms live• Habitat selection: the process by which organisms

actively select habitats in which to live• Species use different criteria to select habitat

– Soil, topography, vegetation, other species• Species have different habitat needs

– Depending on body size, season, etc.• Species survival depends on having suitable habitats


The niche: a multidimensional concept

• Niche: an organism’s use of resources– Along with its functional role in a community– Habitat use, food selection, role in energy and matter

flow, interactions with other individuals• Specialists: have narrow niches and specific needs

– Extremely good at what they do– But vulnerable when conditions change

• Generalists: species with broad niches– They use a wide array of habitats and resources– Survive in many different places


Population size

All populations show characteristicsthat affect their future dynamics

• Population size: the numberof individuals present at agiven time– Can increase, decrease,

cycle, or remain the same

Humans drove passengerpigeons, North America’smost abundant bird, toextinction


Population density

• Population density: the number of individuals in apopulation per unit area

• Large organisms usually have low densities– They need many resources and a large area to survive

• High densities make it easier to find mates– But increase competition and vulnerability to predation– Also increase transmission of diseases

• Low densities make it harder to find mates– But individuals enjoy more space and resources

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Population distribution

• Population distribution(dispersion): spatial arrangementof organisms

• Random: haphazardly locatedindividuals, with no pattern– Resources are widespread

• Uniform: evenly spaced individuals– Territoriality, competition

• Clumped: most common in nature– Arranged according to resources


Four factors of population growth or decline

• Natality: births within the population• Mortality: deaths within the population• Immigration: arrival of individuals from outside the

population– Births and immigration add individuals to a population

• Emigration: departure of individuals from the population– Deaths and emigration remove individuals


Population growth rate

• Growth rate: rate of change in a population’s size perunit time– Equals (birth rate + immigration rate) – (death rate +

emigration rate)– Tells us the net changes in a population’s size per 1000

individuals per year• Growth rate is expressed as a percent:

– Population growth rate * 100%– Populations of different sizes can be compared


Exponential population growth

• Exponential growth: a population increases by afixed percent– Graphed as a J-shaped curve

• It occurs in nature with:– Small populations– Low competition– Ideal conditions

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Limiting factors restrain population growth

• Exponential growth rarely lasts• Limiting factors: physical, chemical, and biological

attributes of the environment limiting population growth• Environmental resistance: all limiting factors together

– Stabilizes the population size at its carrying capacity– Terrestrial animals: space, food, water, mates, shelter,

breeding sites, temperature, disease, predators– Plants: sunlight, moisture, soil chemistry– Aquatic systems: salinity, sunlight, temperature, etc.


Carrying capacity

• Carrying capacity: themaximum populationsize the environmentcan sustain– Determined by

limiting factors• Limiting factors slow

and stop exponentialgrowth– Forms an S-shaped

logistic growth curve


Population density affects limiting factors

• Density-dependent factors: limiting factors whoseinfluence is affected by population density– Increased density increases the risk of predation,

competition for mates, and disease– Results in the logistic growth curve– Environmental resistance has a stronger effect on larger

populations• Density-independent factors: limiting factors whose

influence is not affected by population density– Temperature extremes, floods, fires, and landslides


Perfect logistic curves aren’t often found

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Reproductive strategies vary among species

• Biotic potential: an organism’s capacity to produceoffspring

• K-selected species: species with long gestation periodsand few offspring (i.e., a low biotic potential)– Offspring have a high likelihood of survival– The population stabilizes at or near carrying capacity– Good competitors

• r-selected species: species that reproduce quickly– Have a high biotic potential– Little parental care, populations fluctuate greatly


Population changes affect communities

• Scientists have noticed troubling changes in theenvironment

• As Monteverde dried out, species have disappeared– Golden toads, harlequin frogs, and more had been pushed

from their cloud-forest habitat into extinction– Species from lower, drier habitats moved into the cloud

forest– Population sizes of cloud-forest bird species declined

• Changing climate and disease are causing populationfluctuations and changing the makeup of communities


Conserving biodiversity

• Human development, resource use, and populationpressure are changing populations and communities

• Factors threatening biodiversity have complex social,economic, and political roots– We must understand these factors to solve problems

• Millions of people are working to protect biodiversityand to safeguard ecological and evolutionary processes


Costa Rica’s protection is paying off

• Costa Rica was losing forests at the world’s fastest rate– Now, 25% of its area is under protection

• Ecotourism: tourists visit protected areas

Ecotourism providesthousands of jobs andbillions of dollars toCosta Rica’s economy

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Conclusion

• The fundamentals of evolution and population ecologyare integral to environmental science

• Natural selection, speciation, and extinction helpdetermine Earth’s biodiversity

• Understanding how ecological processes function at thepopulation level is crucial to protecting biodiversity


Ch. 3 Written Assignment• You are a population ecologist studying animals in a national park,

and policymakers are asking for advice on how to apportion thegovernment’s limited conservation funds. How would you rate thefollowing three species, from most vulnerable (and thus most inneed of conservation attention) to least vulnerable? Give reasonsfor your choices.– A bird with an even (1:1) sex ratio that is a habitat generalist– A salamander endemic to the park that lives in high elevation

forest– A fish that specializes on a few types of invertebrate prey and

has a large population size

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