community ecology community structure depends on 4 factors : –physical appearance –species...
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COMMUNITY ECOLOGY
Community Structure
• Depends on 4 factors:
–Physical appearance
–Species diversity
–Species abundance
–Niche structure
Factor 1: Physical Appearance
• A) biomes–Aquatic ecosystemsB) Differences within communities ex. (edge effect)
Edge Effects
• Transitions between ecosystems (ecotones) such as forest and field: differences in sunlight, temp., wind, etc.
• Some animals like “edges” (deer, quail)
Edge Effects• Due to habitat fragmentation,
“edges” are on the rise
• Negative impacts:–Increasing predation, fires, disease,
parasitism, road mortality
–Creates barriers preventing species from finding food, mates
Edge Effects
• Road Mortality
Edge Effects• Preventing mortality by creating “
habitat corridors”
Factor 2: Species Diversity• Number of different species• 3 factors determine diversity:
–Latitude: diversity decreases as you increase latitude (move away from the equator)
–Depth: increasing diversity as increasing depth to approx. 2,000 meters, then decreases with depth, until you get to the bottom
Factor 2: Species Diversity (con.)
3 factors affecting diversity (con.):
pollution: increasing pollution causes a decrease in diversity
Factor 2: Species Diversity
• Other factors: (in general these cause an increase in species diversity)–Increased sunlight–Increased precipitation–Pronounced seasons
Factor 2: Species Diversity• Theory of Island Biogeography
(MacArthur & Wilson)• Species number on an island is
determined by a balance between 2 factors:–Rate of immigration (new species
arriving)–Rate of extinction
• Island Biogeography
Factor 2: Species Diversity (island)
• Rate of immigration and extinction depends on 2 factors:
–Size of the island
–Proximity to the mainland
Factor 2: Species Diversity (island)
• The bigger the island, the more diversity–Small islands are a smaller target for
immigrators & fewer resources
• The closer it is to the mainland, the more diversity–Close island has a higher
immigration rate
Factor 3: Species Abundance
The number of individuals in each species:
although tropical rainforests and coral reefs have high diversity, these areas tend to have low species abundance
Factor 4: Niche Structure• Number of niches (roles) in
ecosystem, similarities and differences between these niches, and species interaction determines niche structure
Factor 4: Niche Structure• Different niches in an ecosystem
(a niche is defined as the role and organism plays in the ecosystem):–Native–Nonnative (exotic, alien, invasive)–Indicator–keystone
Niches• Native: species that normally live
and thrive in a particular ecosystem
Niches• Nonnative: species that migrate or
are accidentally or deliberately introduced into an ecosystem by humans
• Can out-compete native species and crowd them out (invasive species)–Exs.: zebra mussels, kudzu
Niches -- Invasives
• Zebra mussel
Niches -- Invasives
• kudzu
Niches – Indicator Species
• Indicators: species that serve as early warnings to damage to an ecosystem
• Exs. Migratory
• songbirds, frogs
Niches – Indicator Species
• Migratory songbirds respond quickly to environmental change–Habitat fragmentation in both
winter and summer habitat (can’t find suitable nesting sites, increased predation)
–Forest interior loving species
Niches – Indicator Species• Frogs (25% of all known
amphibian sp. are extinct, endangered, or vulnerable)
• Eggs have no protective shells to block out UV rays
• Adults take in water and air through skin, also absorbing pollutants
Niches – Indicator Species
• frogs
Niches: Keystone Species
• Role in ecosystem is more important than abundance or biomass would suggest
• Strong interactions with other species
• Loss could lead to population crashes or extinctions of other sp.
Niches: Keystone Species• Critical Roles:
– Pollination– Seed dispersal– Habitat modification– Predation by top predators– Improve ability for nutrient uptake by
plants– Efficiently recycle animal wastes
Niches: Keystone Species• Habitat modification
Niches: Keystone Species• Predation by top predators
Niches: Keystone Species• Recycling of animal wastes
Niche Structure: Species Interactions
• Species Interactions:– Intraspecific competition– Interspecific competition – Predation– Symbiotic relationships
• Parasitism • Mutualism• commensalism
Niche Structure: Species Interactions
• INTRAspecific competition: competition for resources between members of the same species
Niche Structure: Species Interactions (intraspecific)
• Allelopathy: one species releases a chemical substance to inhibit growth near it. Ex. Black walnut
Niche Structure: Species Interactions (intraspecific)
• Black walnut
Niche Structure: Species Interactions (intraspecific)
• Territoriality:organisms mark and defend an area around home, nest site
Niche Structure: Species Interactions (intraspecific)
• territoriality
Niche Structure: Interspecific
• INTERspecific competition: competition between two or more different species for food, space, or any other limited resource–Fundamental niche: the niche a
species would occupy if there was no competition
Niche Structure: Species Interactions (interspecific)
• The more two species’ niches overlap, the more competition–Competitive exclusion principle:
one species eliminates another in a particular area because they out-compete for limited resources
Niche Structure: Species Interactions (interspecific)
• Competitive
exclusion principle:
Niche Structure: Species Interactions (interspecific)
• How do species reduce competition?– Over time, species that compete for the
same resources evolve adaptations that reduce competition or overlaps of their fundamental niches
– Resource partitioning
Niche Structure: Species Interactions (interspecific)
• Resource partitioning: dividing up of scarce resources so that species can use them at different times, different ways, or different places–Exs. Hawks hunt by day, owls by
night lions take larger prey, while cheetah take smaller
Niche Structure: Species Interactions (interspecific)
• Resource partitioning and niche specialization
Interference Competition
• A species may limit another’s access to some resource
• Ex. Hummingbird’s defending patches of wildflowers by chasing away other humming bird species
Exploitation Competition
• Competing species have equal access to a specific resource, but differ in how fast or efficiently they exploit it
• Ex. humans
Niche Structure: Species Interactions (Predator-Prey)
• Predator-Prey Relationship: as prey pops. Increase, after an initial delay, the predator pops. Increase, eventually causing a decrease in prey, thereby after an initial delay, causing a decrease in predator pops… and so on (cycle)
Niche Structure: Species Interactions (Predator-Prey)
• Predator-prey relationship
Niche Structure: Species Interactions (Predator-Prey)
Predator-prey – didinium & paramecia
Niche Structure: Species Interactions (Predator-Prey)
• Seems to harm prey population, but in reality it often reduce sick, aged, weak members
• Increase food supply for prey and genetic stock (increasing reproductive success and long-term survival
Niche Structure: Species Interactions (Predator-Prey)
• How do predators increase their chance for success of prey acquisition?–Speed, stealth, keen senses,
cooperation, camouflage
Niche Structure: Species Interactions (Predator-Prey)
• Camouflage – preying mantis (in memory of Darwin)
Niche Structure: Species Interactions (Predator-Prey)
• How do prey protect themselves? Prey Avoidance
• Protective shell
Niche Structure: Species Interactions (Prey Adaptations)
• Spines or thorns
Niche Structure: Species Interactions (Prey Adaptations)
• mimicry
Niche Structure: Species Interactions (Prey Adaptations)
mimicry• mimicry
Niche Structure: Species Interactions (Prey Adaptations)
• Poison and warning colors
Niche Structure: Species Interactions (Prey Adaptations)
• camouflage
Niche Structure: Species Interactions (Prey Adaptations)
• Changing color camouflage
Niche Structure: Species Interactions (Prey Adaptations)
• Behavioral strategies
Niche Structure: Species Interactions (Prey Adaptations)
• Schooling, flocking (safety in numbers)
Niche Structure: Species Interactions (parasitism)
• Parasitism: one species feeds on part of another; parasite benefits, host is harmed (rarely killed)
Niche Structure: Species Interactions (ectoparasite)
Niche Structure: Species Interactions (endoparasite)
Niche Structure: Species Interactions (mutualism)
• Mutualism: the two species involved benefit from the relationship (nutritional, protection, reproductive)–Ex. Lichen:fungi collect and hold
moisture, photosynthetic algae provide food
–Birds remove parasites from rhinos–Clownfish gain protection from
anemones and vice versa
Niche Structure: Species Interactions (mutualism)
Niche Structure: Species Interactions (mutualism)
Niche Structure: Species Interactions (commensalism)
• Commensalism: one species benefits and the other one is neither harmed nor benefited
Niche Structure: Species Interactions (commensalism)
Epiphytes: use other plants
for support, to reach
elevations for increased
sunlight
Ecosystems Respond to Change
• Ecological succession: gradual change in species composition of a given area–Primary succession
–Secondary succession
Primary Succession
Ecological succession
• Primary succession–Soil formation begins when
pioneer species attach themselves to bare rock, over time adding organic material and breaking the rock down further
Ecological succession• Pioneer species example:
Ecological succession• After patches of soil are built up,
small grasses and herbs can grow
• Characteristics:– Large pops. Under harsh conditions
– Short lives
Ecological succession
• Next, more grasses, herbs and shrubs, and small trees begin to grow
• Characteristics–Need lots of sunlight (shade
intolerant)
Ecological succession
• Finally a mature forest is in place (oak, hickory) – climax community
• Characteristics–Shade tolerant
Ecological succession
Fig. 8.17, p. 190
Early SuccessionalSpecies
RabbitQuailRingneck pheasantDoveBobolinkPocket gopher
MidsuccessionalSpecies
ElkMooseDeerRuffled grouseSnowshoe hareBluebird
Late SuccessionalSpecies
TurkeyMartinHammond’sFlycatcherGray squirrel
WildernessSpecies
Grizzly bearWolfCaribouBighorn sheepCalifornia condorGreat horned owl
Ecological succession
Ecological succession
• Secondary succession: begins when a natural area has been disturbed or removed
• Examples: abandoned farmland, burned or cut forests, land that has been dammed or flooded, heavily polluted streams
Ecological succession• 3 factors that affect rate of
succession–Facilitation
–Inhibition
–tolerance
Ecological succession• Facilitation: one set of species
makes an area suitable for species with different niche requirements
• Ex. Legumes add nitrogen to soil
Ecological succession
• Inhibition: early species prevent the growth of other species (allelopathy)
Ecological succession
• Tolerance: late successional species are unaffected by earlier species
Ecological Stability
• Stability is maintained only by constant dynamic change in response to changing environmental conditions
• 3 factors affect stability: inertia, constancy, resilience
Ecological Stability• Inertia or persistence: the ability
of a living system to resist disturbance
Ecological Stability
• Constancy: ability of a living system to keep its numbers within limits imposed by available resources
Ecological Stability
• Resilience: ability of a living system to bounce back after an external disturbance
Ecological Stability
• Intermediate Disturbance Hypothesis: moderate disturbance in communities promote greatest species diversity
Ecological Stability
• Intermediate Disturbance Hypothesis
Precautionary Principle
• When evidence indicates that an activity can harm human health, we should take measures to prevent harm even if cause-and-effect relationships have not been fully established scientifically
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