Ecosystems and Communities

Chapter 4

What shapes an ecosystem?

Biotic and Abiotic Factors Biotic Factors living things that affect an organism

–biotic factors affecting bullfrog: plants it eats, birds that might eat it, other species that compete for food or space

What shapes an ecosystem?

Abiotic Factors physical, or nonliving factors that affect organisms

–bullfrog affected by availability of water and temperature of air

Habitat includes both biotic and abiotic factors

Biotic and Abiotic Factors

Biotic Factors

ECOSYSTEM

Abiotic Factors

Niche

An organism’s niche includes: Place in food web Range of temperatures organism needs to

survive Type of food it eats How it obtains food Other species that use it as food Physical conditions necessary for survival When and how it reproduces

Niche

Two species cannot share the same niche in the same habitat.

Different species can occupy similar niches. Ex - three species of warblers live in the

same spruce trees but feed at different elevations and in different part of the trees

Warbler Niches

Bay-Breasted WarblerFeeds in the middlepart of the tree

Cape May WarblerFeeds at the tips of branchesnear the top of the tree

Spruce tree

Community Interactions

Competition same or different species attempt to use an ecological resource in the same place at the same timeresource = necessity of life (water,

nutrients, light, food, space)

Community Interactions Competitive Exclusion Principle - no two

species can occupy the same niche in the same habitat at the same timeDirect competition in nature often

results in winner and loser – losing organism fails to survive

Community Interactions Predation - one organism captures and feeds

on another organism Predator – the one killing and eating Prey – the food Studies show that predation can actually

help maintain diversity. Gray wolves were killed out in many parts of North America. What happened to deer and herbivore populations? What happened to many plant species in North American ecosystems?

Community InteractionsMimicry – a harmless species resembles a poisonous or

distasteful species.

Example: Batesian mimicry – a palatable or harmless species mimics the an unpalatable or harmful model.

Community Interactions Müllerian mimicry - two or more unpalatable

species resemble each other.

Community Interactions Camouflage or cryptic coloration – a passive defense

that makes potential prey difficult to spot against its background.

Aposematic coloration – warning coloration; seen in animals with effective chemical defenses.

Symbiosis When two species live close together. Three types:

Parasitism – one is harmed (host), one benefits (parasite)

Mutualism – both benefit Commensalism – one is neutral, one

benefits

Parasitism examples:

Above: Fleas, ticks, mosquitos and tapeworms are parasites too!

Right: Wheat rust is a parasitic fungus

Mutualism examples:Below: the Oxpecker and the zebra - the oxpecker eats ticks and flys away with a warning scream when danger is near. So the oxpecker gets food and the zebra stays safe and doesn’t have ticks.

Above: the butterfly and the flowers – The butterfly gets the nectar (food) and the flowers get pollinated.

Commensalism examples:

Below: Barnacles on whales – they don’t effect the whale but the barnacles are sessile (the don’t move on their own) and they need to travel through water to get their food.

Above: Sea anemones and clownfish – the sea anemones have nematocysts that sting most organisms but the clownfish is not affected by the stings so the clownfish hide in the anemone so predators can’t get to them.

Ecological Succession

Ecosystem constantly changing due to natural and human disturbancesolder organisms die out and new

organisms move in, causing further changes in the community

Ecological Succession Primary succession – occurs in areas

where no life exists Ex – new rock created by volcano, rock

exposed when glaciers melt

Pioneer species – first to populate new landUsually lichens (algae and fungus) that can break up rock to begin soil formation

Succession changes the composition of species found in a community at a specific time by removing some of them or changing the resources available

Ecological Succession Secondary Succession – occurs when

community is destroyed or altered but soil is still there.

Ex – Fire and clear cutting regrows to mature, stable community called climax community.

Forest Fire Regrowth