Community Interactions

Definitions

Habitat - the type of place where you will normally find a particular species

Characterized by physical & chemical features, such as temperature and salinity & by the array of other species living in it

Ecological community - consists of all the interacting populations within an ecosystem

The biotic component of an ecosystem

What Shapes the Structure of a Community?

1. Interactions between climate & topography -determine the habitat’s temperature, rainfall and soil types

2. Kinds and amounts of food and other resources available

3. Individuals of each species have adaptive traits that allow them to survive and exploit specific resources in the habitat

What Shapes the Structure of a Community?

4. Species in the habitat interact, as in competition, predation and mutually helpful activities

5. Community structure is influenced by the overall pattern of population size, by the arrival and disappearance of species and by physical disturbances to the habitat

The Niche

Sum total of all activities and relationships in which individuals of a species engage as they secure and use the resources required to survive and reproduce

Competition

Interaction that can occur between individuals or species as they attempt to use the same, limited resources, particularly energy, nutrients or space

Competitive Interactions

Intraspecific competition - individuals of the same species compete with one another

Interspecific competition - occurs between populations of different species

Competitive Interactions

Example

Early spring until late summer male black chinned hummingbirds chase all other males and females of its species from his blossoming territory in the Rockies

In late August, rufous hummingbirds of the Pacific Northwest migrate through the Rockies on their way to wintering grounds in Mexico

The rufous males prove to be more aggressive and stronger competitors for the available food - they evict the male black chinned from territories all along the migratory route

Black Chinned and Rufous Hummingbirds

Competitive Exclusion

Two different species differ in their adaptations for acquiring food and avoiding enemies.

Thus one usually competes more effectively for scarce resources than the other

Classic experiment -Russian biologists G. F. Gause -three species of paramecium studied

First grew them separately - then together

Together two of the species both exploited the same food (bacteria) & competed for it intensely- one out competes the other

Sometimes two similar species really have different niches and thus avoid competition

Two species requiring identical resources cannot coexist indefinitely

Concept now called competitive exclusion

Resource Partitioning

An ecologist named MacArthur tested Gauses idea in nature

Studied five species of Warbler that nest in the same type of spruce tress in North
America

Found that each species concentrates its efforts in a specific area of the tree - employing different hunting tactics and nesting a lightly different times

Each species occupies asl ightly smaller nice by dividing up the tree - resource partitioning

Interspecific Competition & Population Size and Distribution

J. Connell worked with barnacles in Scotland

Barnacles of the genus Chthamalus share the rocky shores with the genus Balanus and their niches overlap extensively

Chthamalus dominates the upper shore and Balanus dominates the lower shore

Experiment: Connell scraped off Balanus and the Chthamalus population increased - spreading down to where Balanus once existed

Balanus conquers because it grows faster and bigger

Chthamalus tolerates drier conditions & so on the upper shore only submerged during high tide has the competitive advantage

Predators

Predators kill and eat other organisms

Ecologists sometime include animals that only eat plants (herbivores) because they have a major influence on the size and distribution of plant populations

Predators are being defined in the broadest sense to include grass eating organism like sheep and picas and organisms that filter algae out of the water and consume it.

Most predators are much larger than their prey or hunt collectively such as wolves and lions

Predators are generally lest abundant than prey

Predator-Prey Interactions Shape Evolutionary Adaptations

As prey become more difficult to catch then predators must become better hunters

This coevolution has produced keen eyesight in eagles and earthy camouflage coloration in small mammals

The poisons and bright colors of poison arrow frogs and coral snakes is the result of predation pressure

Predator and Prey Evolve Counteracting Behaviors

In bats and moths we see these adaptations

Bats hunt with extremely high frequency sound pulses - some moths have ears that detect this sound and their activation produces evasive behavior

Some bats try shifting the frequency of their pulse to evade detection - some moths produce their own jamming pulses to interfere with bat echolocation

Camouflage Conceals Predator and Prey

Warning Coloration

Bright coloration that advertises the animals distasteful or poisonous character

Müllerian mimicry - mimicry among different distasteful species

Toxic monarch butterflies have wing patterns strikingly similar to equally distasteful viceroy butterflies

Birds that become ill by consuming one will also avoid the other

Warning Coloration

Batesian Mimicry - mimicry where harmless animals resemble poisonous ones

Hoverflies avoid predation because they resemble a bee

Nonpoisonous scarlet king snakes the deadly coral snake

Startle Coloration

Some insects and vertebrates like the false-eyed frog have evolved patterns of color that closely resemble the eyes of much larger and possibly dangerous animals

If a predator gets close - the prey flashes the eyespots - startles the predator and gives the prey needed time to escape

Symbiosis

Means “living together”- the close interaction between organism of different species for an extended time

Includes - parasitism, mutualism and commensalism

Commensalism -one benefits but the other is neither helped or harmed

Birds using certain trees as roosting sites or barnacles attaching to the skin of a whale

Mutualism -beneficial to both species

Actually a two-way exploitation

Parasitism - one organism benefits by feeding on another

Parasitism

Ectoparasites - feed on the exterior surface of an organism

Lice feed on the bodies of vertebrates

Lamprey feed on the host tissues from the outside

Endoparasites - live internally

Tapeworms

Social (Brood) Parasitism

Cowbirds and cuckoos lay eggs in the nests of other birds

Host parents raise the brood parasite as if it were their own

Commensalism

Clownfishes form symbiotic relationship with sea anemones

The clownfish gains protection of the tentacles and gleans scraps of food

Mutualism

Positive benefits flow both directions - abound in nature

A tree provides a birdwith food and the bird in turn disperses the seeds of the plant to new germination sites

Lichen - often seen as brightly colored patches on rocks - mutualistic association of alga and fungus- here the fungus provides support and protection and the photosynthetic alga provides food

Mutualism may be obligatory - one species may not be able to grow and reproduce without the other

Each yucca plant - only pollinated by one species of the yucca moth genus

Also larval stages of the moth grow only in the yucca plant - eat only yucca seeds

Keystone Species

The dominant species typically a predator dictates community structure

Some keystone species manipulate the environment in ways that create new habitats for other species

Beavers do this by changing the flow of water in streams and flooding areas

Keystone Species & Competition

Robert Paine- placed sea star and its prey in control plots

When all seastars were removed - mussels took over & crowded out seven other invertebrate species

Mussels are the main prey of sea stars - & mussels become the strongest competitors when sea stars are absent

Conclusion is that sea star predation normally maintains diversity of prey species because it blocks competitive exclusion by mussels

Succession

Mature terrestrial ecosystem - populations interact with one another and with the nonliving environment in many ways

Succession is a structural change in a community and its nonliving environment over time

Assemblages of plants and animals replace one another in a sequence that is somewhat predictable

Succession is preceded by a disturbance or event that disrupts the ecosystem either by altering its community, its abiotic structure or both

Primary Succession

Begins with a complete absence of life, including soil organisms

Freshly exposed rock

Begins with lichens - trap soil & erode rock

Now substrate for mosses

Dead mosses- layer of humus - then grasses

Dead grasses- more humus - now larger shrubs

Secondary Succession

Begins with some life already present

Agriculture most common initiator

e.g.. Old-field succession of abandon farms

Revert to tall grasses - then weeds &shrubs

Next trees such as aspens & pines

These are eventually replaced by trees whose seedlings can tolerate shade

Called Climax stage of succession