community ecology community structure depends on 4 factors : –physical appearance –species...

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 – Habitat Fragmentation

http://www.youtube.com/watch?v=WGWFh6vCd7I

Edge Effects• Nest parasitism

http://www.youtube.com/watch?v=4Mb0GOITRUU

Edge Effects

• Road Mortality

Edge Effects• Preventing mortality by creating “

habitat corridors”

http://www.youtube.com/watch?v=XYmZpjYDZyE

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

http://www.youtube.com/watch?v=nmU7etSYYqI

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


• 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


• 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• Pollination and seed dispersal

http://www.youtube.com/watch?v=-7ijI-g4jHg

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


• Black walnut


• Territoriality:organisms mark and defend an area around home, nest site


• 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


• Competitive

exclusion principle:


• 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


• 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


• 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)


• Predator-prey relationship


Predator-prey – didinium & paramecia


• 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


• How do predators increase their chance for success of prey acquisition?–Speed, stealth, keen senses,

cooperation, camouflage


• Camouflage – preying mantis (in memory of Darwin)

http://www.youtube.com/watch?v=pNcIUIULafw


• How do prey protect themselves? Prey Avoidance

• Protective shell

Niche Structure: Species Interactions (Prey Adaptations)

• Spines or thorns


• mimicry


mimicry• mimicry


• Poison and warning colors


• camouflage


• Changing color camouflage

http://www.youtube.com/watch?v=pVIVIq4F3x0


• Behavioral strategies


• 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 (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

http://www.youtube.com/watch?v=4RsMyVavT2Q

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


• Next, more grasses, herbs and shrubs, and small trees begin to grow

• Characteristics–Need lots of sunlight (shade

intolerant)


• Finally a mature forest is in place (oak, hickory) – climax community

• Characteristics–Shade tolerant

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



• 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


• Inhibition: early species prevent the growth of other species (allelopathy)


• 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


• Constancy: ability of a living system to keep its numbers within limits imposed by available resources


• Resilience: ability of a living system to bounce back after an external disturbance


• Intermediate Disturbance Hypothesis: moderate disturbance in communities promote greatest species diversity


• 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

community ecology community structure depends on 4 factors : –physical appearance –species...

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native species

species interaction

species diversity islandthe

species diversityother

low species abundancefactor

high diversity

increasing depth

summer habitat