Ecology and evolution: Populations, communities, and biodiversity

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• Ecology and evolution Populations, communities,
  and biodiversity

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This lecture will help you understand

• How evolution generates biodiversity
• Speciation, extinction, and the biodiversity
  crisis
• Population ecology
• Community ecology
• Species interactions
• Conservation challenges
• Evolution by natural selection

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Key Words
adaptation adaptive trait age distribution age
structure age structure diagrams allopatric
speciation anthropogenic artificial
selection biodiversity biological
diversity biosphere biotic potential carnivores ca
rrying capacity climax community clumped
distribution community competition decomposers
host immigration interspecific competition intrasp
ecific competition invasive species keystone
species K-strategist limiting factors logistic
growth mass extinction mutations mutualism natural
selection niche omnivores parasite parasitism
density dependent detritivores ectoparasites Emigr
ation endemic endoparasites environmental
resistance evolution exponential
growth extinction food chain food
web fossil fossil record growth rate habitat
selection habitats herbivores heritable
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Key Words
sex ratio speciation species succession symbioses
tertiary consumers trophic levels uniform
distribution
phylogenetic trees pioneer species pollination pop
ulation density population dispersion population
distribution population growth curves population
size predation predator prey primary
consumers primary succession random
distribution resource partitioning r-strategists s
econdary consumers secondary succession
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Central Case Striking Gold in a Costa Rican
Cloud Forest

• The golden toad of Monteverde, discovered in
  1964, had disappeared 25 years later.
• Researchers determined that warming and drying of
  the forest was most likely responsible for its
  extinction.
• As the global climate changes, more such events
  can be expected.

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Biodiversity

• Biodiversity, or biological diversity, is the sum
  of an areas organisms, considering the diversity
  of species, their genes, their populations, and
  their communities.
• A species is a particular type of organism a
  population or group of populations whose members
  share certain characteristics and can freely
  breed with one another and produce fertile
  offspring.

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Biodiversity

• Costa Ricas Monteverde cloud forest is home to
  many species and possesses great biodiversity.

Figure 5.1
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Natural selection

• Natural selection rests on three indisputable
  facts
• Organisms produce more offspring than can
  survive.
• Individuals vary in their characteristics.
• Many characteristics are inherited by
  offspring from parents.

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Natural selection

• THEREFORE, logically
• Some individuals will be better suited to
  their environment they will survive and
  reproduce more successfully.
• These individuals will transmit more genes to
  future generations.
• Future generations will thus contain more
  genes from better-suited individuals.
• Thus, characteristics will evolve over time to
  resemble those of the better-suited ancestors.

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Natural selection

• Fitness the likelihood that an individual will
  reproduce
• and/or
• the number of offspring an individual
  produces over its lifetime
• Adaptive trait,
• or adaptation a trait that increases an
  individuals fitness

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Natural selection

• Evidence of natural selection is all around us
• In nature
• Diverse bills have evolved among species of
  Hawaiian honeycreepers.

Figure 4.23a
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Beak Types Resulting From Natural Selection
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Natural selection

• Evidence of natural selection is all around us
• and in our domesticated organisms.

Dog breeds, types of cattle, improved crop
plantsall result from artificial selection
(natural selection conducted by human breeders).
Figure 4.23b
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Speciation

• The process by which new species come into being
• Speciation is an evolutionary process that has
  given Earth its current species richnessmore
  than 1.5 million described species and likely
  many million more not yet described by science.
• Allopatric speciation is considered the dominant
  mode of speciation, and sympatric speciation also
  occurs.

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Allopatric speciation

• 1. Single interbreeding population
• 2. Population divided by a barrier
  subpopulations isolated

Figure 5.2
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Allopatric speciation

• 3. The two populations evolve independently,
  diverge in their traits.
• 4. Populations reunited when barrier removed, but
  are now different enough that they dont
  interbreed.

Figure 5.2
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Allopatric speciation

• Many geological and climatic events can serve as
  barriers separating populations and causing
  speciation.
• on.

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Stanley Miller's experiment animation.
Click to view animation.
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Stabilizing Selection
Click to view animation.
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Disruptive Selection
Click to view animation.
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Niches and Natural Selection
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Various Niches and Their Adaptations
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Geographic Separation
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Mimicry
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Phylogenetic trees

• Lifes diversification results from countless
  speciation events over vast spans of time.
• Evolutionary history of divergence is shown with
  diagrams called phylogenetic trees.
• Similar to family genealogies, these show
  relationships among organisms.

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Phylogenetic trees

• These trees are constructed by analyzing patterns
  of similarity among present-day organisms.
• This tree shows all of lifes major groups.

Figure 5.4
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Phylogenetic trees

• Within the group Animals in the previous slide,
  one can infer a tree of the major animal groups.

Figure 5.4
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Phylogenetic trees

• And within the group Vertebrates in the previous
  slide, one can infer relationships of the major
  vertebrate groups, and so on

Figure 5.4
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Extinction

• Extinction is the disappearance of an entire
  species from the face of the Earth.
• Average time for a species on Earth is 110
  million years.Species currently on Earth the
  number formed by speciation minus the number
  removed by extinction.

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Extinction

• Some species are more vulnerable to extinction
  than others
• Species in small populations
• Species adapted to a narrowly specialized
  resource or way of life
• Monteverdes golden toad was apparently such a
  specialist, and lived in small numbers in a small
  area.

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Extinction

• Some species are more vulnerable to extinction
  than others
• Species in small populations
• Species adapted to a narrowly specialized
  resource or way of life
• Monteverdes golden toad was apparently such a
  specialist, and lived in small numbers in a small
  area.

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Lifes hierarchy of levels

• Life occurs in levels
• from the atom up to
• the molecule to
• the cell to
• the tissues to
• the organs to
• the organism

Figure 5.7
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Lifes hierarchy of levels

• and from the organism to the population to
• the community to
• the ecosystem to
• the biosphere.
• Ecology deals with these levels, from the
  organism up to the biosphere.

Figure 5.7
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Ecology

• The study of
• the distribution and abundance of organisms,
• the interactions among them,
• and the interactions between organisms and
  their abiotic environments
• Ecology is NOT environmental advocacy!
• ( a common MISUSE of the term)

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Habitat and niche

• Habitat the specific environment where an
  organism lives (including living and nonliving
  elements rocks, soil, plants, etc.)
• Habitat selection the process by which
  organisms choose habitats among the options
  encountered
• Niche an organisms functional role in a
  community (feeding, flow of energy and matter,
  interactions with other organisms, etc.)

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Population ecology

• Population a group of individuals of a species
  that live in a particular area
• Several attributes help predict population
  dynamics (changes in population)
• Population size
• Population density
• Population distribution
• Age structure
• Sex ratio

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Population size

• Number of individuals present at a given
  timePopulation size for the golden toad was
  1,500 in 1987, and zero a few years later.

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Population density

• Number of individuals per unit area or,
• Number of individuals per unit volume
• Population density for the harlequin frog
  increased locally as streams dried and frogs
  clustered in splash zones.

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Population distribution

• Spatial arrangement of individuals

Clumped
Random
Uniform
Figure 5.8
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Age structure

• Or age distribution relative numbers of
  individuals of each age or age class in a
  population
• Age structure diagrams, or age pyramids, show
  this information.

Figure 5.9
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Age structure
Pyramid weighted toward young population growing
Pyramid weighted toward old population declining
Figure 5.9
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Sex ratio

• Ratio of males to females in a population
• Even ratios (near 50/50) are most common.
• Fewer females causes slower population growth.
• Note human sex ratio biased toward females at
  oldest ages.

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Population growth

• Populations grow, shrink, or remain stable,
  depending on rates of birth, death,
  immigration, and emigration.
• (birth rate immigration rate)
• (death rate emigration rate)
• population growth rate

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Exponential growth

• Unregulated populations increase by exponential
  growth
• Growth by a fixed percentage, rather than a
  fixed amount.
• Similar to growth of money in a savings account

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Exponential growth in a growth curve

• Population growth curves show change in
  population size over time.
• Scots pine shows exponential growth

Figure 5.10
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Limits on growth

• Limiting factors restrain exponential population
  growth, slowing the growth rate down.
• Population growth levels off at a carrying
  capacitythe maximum population size of a given
  species an environment can sustain.
• Initial exponential growth, slowing, and
  stabilizing at carrying capacity is shown by a
  logistic growth curve.

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Logistic growth curve
Figure 5.11
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Population growth Logistic growth

• Logistic growth (shown here in yeast from the
  lab) is only one type of growth curve, however.

Figure 5.12a
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Population growth Oscillations

• Some populations fluctuate continually above and
  below carrying capacity, as with this mite.

Figure 5.12b
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Population growth Dampening oscillations

• In some populations, oscillations dampen, as
  population size settles toward carrying capacity,
  as with this beetle.

Figure 5.12c
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Population growth Crashes

• Some populations that rise too fast and deplete
  resources may then crash, as with reindeer on St.
  Paul Island.

Figure 5.12d
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Density dependence

• Often, survival or reproduction lessens as
  populations become more dense.
• Density-dependent factors (disease, predation,
  etc.) account for the logistic growth curve.

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Biotic potential and reproductive strategies

• Species differ in strategies for producing
  young.
• Species producing lots of young (insects, fish,
  frogs, plants) have high biotic potential.
• Others, such as mammals and birds, produce few
  young.
• However, those with few young give them more
  care, resulting in better survival.

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Biotic Potential
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Survivorship
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K-strategists
Terms come from K symbol for carrying
capacity. (Populations tend to stabilize near K.)
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r-Selected

• r intrinsic rate of population increase.
  (Populations can potentially grow fast, have high
  r.)

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Community ecology

• Ecologists interested in how populations or
  species interact with one another study community
  ecology.
• Community a group of populations of different
  species that live in the same place at the same
  time
• e.g., Monteverde cloud forest
  communitygolden toads, quetzals, trees,
  ferns, soil microbes, etc.

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Roles in communities Producers

• By eating different foods, organisms are at
  different trophic levels, and play different
  roles, in the community
• Plants and other photosynthetic organisms are
  producers.

Figure 5.14b
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Primary consumers

• Animals that eat plants are primary consumers, or
  herbivores, and are at the second trophic level.

Figure 5.14b
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Secondary consumers

• Animals that eat herbivores are secondary
  consumers, at the third trophic level.

Figure 5.14b
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Detritivores and decomposers

• Detritivores and decomposers eat nonliving
  organic matter they recycle nutrients.

Figure 5.14b
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Trophic levels

• Together these comprise trophic levels.

Figure 5.14b
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Food chains and webs

• We can represent feeding interactions (and thus
  energy transfer) in a community
• Food chain Simplified linear diagram of who eats
  whom
• Food web Complex network of who eats whom

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Food web for an eastern deciduous forest
Figure 5.14a
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Keystone species

• Species that have especially great impacts on
  other community members and on the communitys
  identity
• If keystone species are removed, communities
  change greatly.

A keystone holds an arch together.
Figure 5.15a
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Keystone species

• When the keystone sea otter is removed, sea
  urchins overgraze kelp and destroy the kelp
  forest community.

Figure 5.15b
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Balance of Life
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Predation

• One species, the predator, hunts, kills, and
  consumes the other, its prey.

Figure 5.16
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Predation drives adaptations in prey
Cryptic coloration Camouflage to hide from
predators
Warning coloration Bright colors warn that prey
is toxic
Mimicry Fool predators (here, caterpillar mimics
snake)
Figure 5.18
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Competition

• When multiple species seek the same limited
  resource
• Interspecific competition is between two or
  more species.
• Intraspecific competition is within a
  species.
• Usually does not involve active fighting, but
  subtle contests to procure resources.

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Interspecific competition

• Different outcomes
• Competitive exclusion one species excludes the
  other from a resource.
• Species coexistence both species coexist at a
  ratio of population sizes, or stable equilibrium.

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Competitive Exclusion Principle
Click to view animation.
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Interspecific competition

• Adjusting resource use, habitat use, or way of
  life over evolutionary time leads to
• Resource partitioning species specialize in
  different ways of exploiting a resource.
• Character displacement physical characters
  evolve to become different to better
  differentiate resource use.

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Resource partitioning

• Tree-climbing bird species exploit insect
  resources in different ways.

Figure 5.20
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Parasitism

• One species, the parasite, exploits the other
  species, the host, gaining benefits and doing
  harm.

Figure 5.21
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Mutualism

• Both species benefit one another.
• Hummingbird pollinates flower while gaining
  nectar for itself.

Figure 5.22
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Mutualism
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Succession

• A series of regular, predictable, quantifiable
  changes through which communities go
• Primary succession Pioneer species colonize a
  newly exposed area (lava flows, glacial retreat,
  dried lake bed).
• Secondary succession The community changes
  following a disturbance (fire, hurricane,
  logging).

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Primary aquatic succession

• 1. Open pond
• 2. Plants begin to cover surface sediment
  deposited
• 3. Pond filled by sediment vegetation grows over
  site

Figure 5.24
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Secondary terrestrial succession
Figure 5.23
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Succession
Click to view animation.
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Ecosystem Characteristics at Immature and Mature
Stages of Ecological Succession
Characteristic Ecosystem Structure Plant
size Species diversity Trophic
structure Ecological niches Community
organization (number of interconnecting
links) Ecosystem Function Biomass Net primary
productivity Food chains and webs Efficiency of
nutrient recycling Efficiency of energy use
Immature Ecosystem (Early Successional
Stage) Small Low Mostly producers, few
decomposers Few, mostly generalized Low Lo
w High Simple, mostly plant
herbivore with few decomposers Low Low
Immature Ecosystem (Late Successional
Stage) Large High Mixture of producers,
consumers, and decomposers Many, mostly
specialized High High Low Complex,
dominated by decomposers High High
Table 8-1Page 158
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Invasive species

• A species that spreads widely and rapidly becomes
  dominant in a community, changing the communitys
  normal functioning
• Many invasive species are non-native, introduced
  from other areas.
• Purple loosestrife invades a wetland.

Figure 5.25
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Climate change and Monteverde

• Monteverdes cloud forest become drier in the
  1970s1990s.

Stream flow fell
Number of dry days rose
From The Science behind the Stories
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Climate change and Monteverde

• Cool ocean low clouds mountains receive
  moisture
• Warm ocean high clouds mountains get less
  moisture

From The Science behind the Stories
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Viewpoints Conservation of Monteverde?
Robert Lawton
Nathaniel Wheelwright
A few committed people can have an impact.
Conservation efforts must take into account local
social aspirations. Conservation can lead to
economic success. But local conservation is not
enough.
Whatever negative local impact the steady
onslaught of ecotourists may have on resplendent
quetzals and howler monkeys, it is more than
compensated for by inspiring people to appreciate
tropical forests and their own natural heritage.
From Viewpoints
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Conclusions Challenges

• Earths biodiversity faces a mass extinction
  event caused by human actions.
• Climate change may alter communities and cause
  species extinctions.
• Invasive species pose a new threat to community
  stability.
• Conservation efforts need to consider local
  economies and social conditions in order to
  succeed.
• Evolution and natural selection provide a strong
  explanation for how Earths life diversified.

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Conclusions Solutions

• There is still time to avoid most species
  extinctions threatened by human actions.
• Studies like those at Monteverde are clarifying
  the effects of climate change.
• Ecological restoration efforts can remove
  invasive species and restore original
  communities.
• Many conservation efforts today are locally run
  or promote local economies.

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QUESTION Review

• Allopatric speciation requires?
• a. Natural selection
• b. More than two populations
• c. Some kind of barrier separating populations
• d. Sex ratio bias in one population

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QUESTION Review

• Which is a K-strategist?
• a. A dragonfly that lays 300 eggs and flies away
• b. An oak tree that drops its acorns each year
• c. A bamboo plant that flowers only once every 20
  years
• d. A human who raises three children
• e. A fish on the second trophic level

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QUESTION Review

• Which of the following lists of trophic levels is
  in the correct order?
• a. Producer, secondary consumer, herbivore
• b. Producer, herbivore, secondary consumer
• c. Secondary consumer, producer, detritivore
• d. Herbivore, carnivore, producer

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QUESTION Review

• Primary succession would take place on all of the
  following EXCEPT?
• a. The slopes of a Hawaiian volcanos new lava
  flow
• b. A South Carolina coastal forest after a
  hurricane
• c. Alaskan land just uncovered as a glacier melts
• d. A new island formed by falling levels of a
  reservoir in Ohio

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QUESTION Weighing the Issues

• Can we continue raising the Earths carrying
  capacity for humans by developing technology and
  using resources more efficiently?
• a. Yes, our growth can continue indefinitely.
• b. Our growth can continue some more, but will
  eventually be halted by limiting factors.
• c. No, we cannot raise Earths carrying capacity
  for ourselves any longer.

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QUESTION Weighing the Issues

• Are national parks and preserves the best way to
  conserve biodiversity?
• a. Yes, because species depend on their habitats
  and intact communities being protected.
• b. No, because climate change can ruin
  conservation efforts if it changes conditions
  inside preserves.
• c. Ecotourism and encouraging local interest in
  conservation is more important than establishing
  parks.

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QUESTION Interpreting Graphs and Data

• You would expect this population to be?
• a. Growing rapidly
• b. Shrinking rapidly
• c. Stable in size
• d. Oscillating in size

Figure 5.9
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QUESTION Interpreting Graphs and Data

• How can you tell that this population growth
  curve shows exponential growth?
• a. Population is increasing.
• b. Data points match curve closely.
• c. Population is rising by the same number
  during each interval.
• d. Population is rising by the same percentage
  during each interval.

Figure 5.10
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QUESTION Interpreting Graphs and Data

• This shows growth ending at a(n)
  .
• a. exponential carrying capacity
• b. intrinsic equilibrium
• c. logistic carrying capacity
• d. runaway equilibrium
• e. logistic extinction

Figure 5.12a
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QUESTION Viewpoints

• What is the most important lesson we can learn
  from the Monteverde preserve?
• a. Preserves do little good if species can become
  extinct inside them.
• b. Climate change means that we will need more
  than preserves to save all species.
• c. Ecotourism and local participation can make
  for successful conservation.