Evolution, Biodiversity, and Community Processes

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Evolution, Biodiversity, and Community Processes

• La Cañada High School
• Dr. E

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Biodiversity
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How do we get Biodiversity?
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Biodiversity

• 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

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Interpretations of Speciation

• Two theories
• 1. Gradualist Model (Neo-Darwinian)
• Slow changes in species overtime
• 2. Punctuated Equilibrium
• Evolution occurs in spurts of relatively rapid
  change

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Adaptive Radiation

• Emergence of numerous species from a common
  ancestor introduced to new and diverse
  environments
• Example
• Hawaiian Honeycreepers

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Convergent Evolution

• Species from different evolutionary branches may
  come to resemble one another if they live in very
  similar environments
• Example
• 1. Ostrich (Africa) and Emu (Australia).
• 2. Sidewinder (Mojave Desert) and
• Horned Viper (Middle East Desert)

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Coevolution

• Evolutionary change
• One species acts as a selective force on a second
  species
• Inducing adaptations
• that act as selective force on the first species
• Example
• Wolf and Moose
• Acacia ants and Acacia trees
• Yucca Plants and Yucca moths
• Lichen

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Extinction

• 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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Extinction

• Background extinction - species disappear at a
  low rate as local conditions change
• Mass extinction - catastrophic, wide-spread
  events --gt abrupt increase in extinction rate
• Five mass extinctions in past 500 million years
• Adaptive radiation - new species evolve during
  recovery period following mass extinction

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Mass Extinctions
http//www.geog.ouc.bc.ca/physgeog/contents/9h.htm
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Date 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
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Equilibrium Theory of Biodiversity

• Diversity is a balance of factors that increase
  diversity and factors that decrease diversity
• Production of new species (speciation), and
  influx can increase diversity
• Competitive exclusion, efficient predators,
  catastrophic events (extinction) can decrease
  diversity
• Physical conditions
• variety of resources
• Predators
• environmental variability

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Comparison of Two Communities

• Richness (number of species)
• Relative abundance
• How do we describe these differences?

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Biogeographical Changes

• Richness declines from equator to pole
• Due to
• Evolutionary history
• Climate

Fig 53.23 Bird species numbers
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Geographic (Sample) Size

• Species-area curve
• The larger the geographic area, the greaterthe
  numberof species

Fig. 23.25 North American Birds
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Species Richness on Islands

• Depends on
• Rate of immigration to island
• Rate of extinction on island
• These in turn depend on
• Island size
• Distance from mainland

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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?

• Niche opening
• No competition
• Endemics not utilizing resources
• Accessibility to colonists

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Theory 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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Theory of Island Biogeography

1. Smaller islands have lower total populations
2. Probability of extinction increases with lower
   population
3. Smaller islands have lower species diversity

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Theory of Island Biogeography

1. Islands further from mainland have lower
   immigration rates
2. More distant islands have lower species diversity

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Community Relationships
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• Niche is
• the 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
• Range of tolerance for various physical and
  chemical conditions
• Types of resources used
• Interactions with living and nonliving components
  of ecosystems
• Role played in flow of energy and matter cycling

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Niche
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Types 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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r and k strategists

• Depending upon the characteristics of the
  organism, organisms will follow a biotic
  potential or carrying capacity type reproductive
  strategy
• The r-strategists
• High biotic potential reproduce very fast
• Are adapted to live in a variable climate
• Produce many small, quickly maturing offspring
  early reproductive maturity
• Opportunistic organisms
• The K-strategists
• Adaptations allow them to maintain population
  values around the carrying capacity
• They live long lives
• Reproduce late
• Produce few, large, offspring

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Types of Species

• Native species normally live and thrive in a
  particular ecosystem
• Nonnative species are introduced - can be called
  exotic or alien
• Indicator species serve as early warnings of
  danger to ecosystem- birds amphibians
• Keystone species are considered of most
  importance in maintaining their ecosystem

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Nonnative Species

• Nonnative plant species are invading the nation's
  parks at an alarming rate, displacing native
  vegetation and threatening the wildlife that
  depend on them
• At some, such as Sleeping Bear Dunes National
  Lakeshore in Michigan, as much as 23 percent of
  the ground is covered with alien species, and the
  rate of 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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Competition

• Any interaction between two or more species for a
  resource that causes a decrease in the population
  growth or distribution of one of the species
• Resource competition

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Competition
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Resource Competition
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Competition

• Any interaction between two or more species for a
  resource that causes a decrease in the population
  growth or distribution of one of the species
• Resource competition
• Preemptive competition

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Competition

• Any interaction between two or more species for a
  resource that causes a decrease in the population
  growth or distribution of one of the species
• Resource competition
• Preemptive competition
• Competitive exclusion

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Competitive Exclusion
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Competition

• Any interaction between two or more species for a
  resource that causes a decrease in the population
  growth or distribution of one of the species
• Resource competition
• Preemptive competition
• Competition exploitation
• Interference competition

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Competition
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PREDATION
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Predator Adaptations

• Prey detection and recognition
• sensory adaptations
• distinguish prey from non-prey

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Predator Adaptations

• Prey detection and recognition
• sensory adaptations
• distinguish prey from non-prey
• Prey capture
• passive vs. active
• individuals vs. cooperative

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Predator 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 Adaptations

• Avoid detection
• camouflage, mimics,
• diurnal/nocturnal

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Prey Adaptations

• Avoid detection
• camouflage, mimics,
• diurnal/nocturnal
• Avoid capture
• flee
• resist
• escape

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Prey Adaptations

• Avoid detection
• camouflage, mimics,
• diurnal/nocturnal
• Avoid capture
• flee
• resist
• escape
• Disrupt handling (prevent being eaten)
• struggle?
• protection, toxins

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Herbivory

• Herbivore needs to find most nutritious
• circumvent plant defenses

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Herbivory

• Herbivore 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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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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Mutualism

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

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Mutualism

• Increase birth rates
• Decrease death rates
• Increase equilibrium population densities,
• Raise the carrying capacity

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Pollination

• 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 and Yucca Moth

• Yuccas only pollinator is the yucca moth. Hence
  entirely dependent on it for dispersal.
• Yucca moth caterpillars only food is yucca
  seeds.
• Yucca moth lives in yucca and receives shelter
  from plant.

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Lichen (Fungi-Algae)

• Symbiotic relationship of algae and
  fungaeresults in very different growth formas
  with and without symbiont.
• What are the benefits to the fungus?

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Nitrogen Fixation

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

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Obligatory 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 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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Commensalists

• 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 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 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 Succession

• Primary 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 Succession
Gradual changing environment in favor of new /
different species / communities
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Primary 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 SuccessionGlacier Retreat
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Secondary 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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Disturbance

• Event that disrupts an ecosystem or community
• Natural disturbance
• tree falls, fires, hurricanes, tornadoes,
  droughts, floods
• Humancaused disturbance
• deforestation, erosion, overgrazing, plowing,
  pollution,mining
• Disturbance can initiate primary and/or secondary
  succession

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Ecological Stability

• Carrying Capacity maximum number of individuals
  the environment can support

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Ecological Stability - Stress

1. Drop in Primary Productivity
2. Increased Nutrient Losses
3. Decline or extinction of indicator species
4. Increased populations of insect pests or disease
   organisms
5. Decline in Species diversity
6. Presence of Contaminants

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