Biology 2B - Ecology

Communities and biomes

Ecosystems

HabitatParticular area in which a population lives

Abiotic factor Non living factors eg temperature, rainfall

PopulationAll the organisms from one species in an ecosystem

CommunityAll the organisms in an ecosystem

Environment All the abiotic factors

Biotic factorLiving factors eg predation, competition

Ecosystem is a term that describes ecological systems consisting of interacting organisms and their physical environment

Aquatic habitatsAquatic habitats come in many forms: lakes, rivers, wetlands, marshes, lagoons, streams, rivers, and swamps. Where freshwater mixes with saltwater you'll find mangroves, salt marshes, and mud flats.

Seas and oceans stretch from pole to pole and reach around the globe. They cover more than 70 percent of the Earth's surface and hold in excess of 300 million cubic miles of water. Scattered throughout these vast waters are islands.

Coral reefs are made up of millions of tiny coral polyps -- animals that together form vast colonies and secrete the limestone deposits. Reefs form in shallow, warm-water seas around the world. There are several types of reef including barrier reefs, fringe reefs, and atolls.

Beaches and coasts lie at the threshold between land and sea where wildlife adapts to a constantly changing coastline and sways to the rhythms of the tides.

Terrestrial habitatsDeserts and scrublands are landscapes that have scarce precipitation. Scrublands are semi-arid habitats that are dominated by scrub vegetation such as grasses, shrubs, and herbs.

Forests and woodlands are habitats dominated by trees. There are many different types of forests—temperate, tropical, cloud, coniferous, boreal.

Tundra is a cold habitat characterized by low temperatures, short vegetation, long winters, brief growing seasons, and limited drainage. Arctic tundra is located near the North Pole and extends southward to the point where coniferous forests grow. Alpine tundra is located on mountains around the world at elevations that are above the tree line.

Alpine, or montane, habitats occur in highlands and mountain ranges around the world.

Structural classification of communities

Type and height of tallest layer

Percentage foliage cover of tallest layerVery dense

(100 - 70%)Dense (70 - 50%)

Medium (50 - 30%)

Sparse (30 -10%)

Very sparse ( 10%)

Trees 10 – 30 m

Trees 10m = low

Trees 30m = tall

Closed forest

Low

Tall

Forest

Low

Tall

Open forest

Low

Tall

Woodland

Low

Tall

Open woodland

Low

-

Shrubs 2m

Shrubs 0.25 - 2m

Closed scrub

Closed heathland

Scrub

Heathland

Open scrub

Open heathland

Tall shrubland

Shrubland

Tall open shrubland

Open shrubland

Hummock grasses - - - Hummock grassland

Open hummock grassland

Herbaceous layer

Mainly grasses

Mainly sedges

Mainly herbs

Mainly ferns

Closed grassland

Closed sedgeland

Closed herbland

Closed fernland

Grassland

Sedgeland

Herbland

Fernland

Open grassland

Open sedgeland

Open herbland

-

Very open grassland

Very open sedgeland

Very open herbland

-

Biomes

Communities with similar abiotic factors have similar characteristics, although they contain different species of plants and animals.

Characteristics of terrestrial biomes

Changes in communities

Ecosystems change:Abiotic factors may vary – eg light, water, temperature, salinity, tidesThese may vary cyclically eg day/night; monthly,

seasonally, over longer periods, or catastrophically (eg fire, flood, volcanic eruption, ice age, etc)

Biotic factors may vary –Numbers of • Producers • Prey species (1st order consumers)• Predators (high order consumers)

Everything in an ecosystem is linked

• A change in one factor can lead to changes in other factors – this is called the domino effect

eg decreased rainfall decrease in vegetation decrease in herbivores (prey species) decrease in predators

eg removal of predators (hunting or biomagnification) increase prey species (plague) decrease vegetation decrease in herbivores due to no food

• Key species a species whose removal negatively affects an entire ecosystem eg otters in kelp forests – when hunted to extinction, sea urchin numbers increased so much that they destroyed the kelp decrease in the other species depending on kelp for food or shelter

Changes in ecosystems – human interference

Human presence disrupts ecosystems in many ways including:• Loss of predators removal of predators (sg spiders, wolves) can

lead to population explosions of prey species• Introduction of new carnivore eg foxes, cats, dogs loss of

native wildlife• Introduction of new herbivore eg rabbit, sheep, may out-

compete natives loss of native species; may cause over grazing as no native predators erosion

• Introduction of new producer eg brambles, prickly pear, may out compete natives (as often not edible to consumers) loss of native plant and animal species (now not enough food for them); aquatic plants eg duckweed may block rivers

Changes in ecosystems - water

• Damschanges distribution of populations in ecosystems – can get animals accumulating around dams over grazing near the water source; loss of original ecosystem in flooded area

• Presence of bores lowers water table; increases number of animals around bore over grazing near the water source

• Tailing dams kills wildlife that tries to use it as water• Removing water for human use lowers amount of water in

river/streams eg Murray not enough water to maintain ecosystem• Filling in wetlands destroys ecosystem; loss of habitat for

migrating birds; damage to neighbouring ecosystems as wetlands act as filters to remove pollutants and excess nutrients

Changes in ecosystems - clearing

Loss of trees loss of habitat & nesting places as well as the following

• Loss of topsoil (= erosion) loss of fertility decreased producers decreased biomass in the whole ecosystem

• Rise of water table water logging in low lying areas, increased soil salinity as salts are brought up with the water

• Increased soil salinity loss of fertility decreased producers decreased biomass in the whole ecosystem

• Increased water salinity loss of fertility decreased producers decreased biomass in the whole ecosystem; poisoning of consumers, loss of aquatic life

Changes in ecosystems -agriculture

Farming agricultural practices include• Monoculture presence of only one species in the crop,

decreases biodiversity, encourages population explosions or plagues of pest species eg mice, locusts, in the long term reduces soil fertility

• Killing insects (eg pesticides) disrupts ecosystems by destroying food source of higher order species (eg owls, wattle birds); can lead to ecological magnification

• Loss of dead/decaying matter loss of fertility, loss of decomposers soil problems reduction in producers reduction in consumers

• Fertiliser use chemical poisoning of plants or animals (eg high phosphate fertilisers kill many native trees; run-off into rivers can cause eutrophication (algal blooms)

Changes in ecosystems – climate change

Climate change changes in temperature, rainfall & humidity – also affects water availability

• Increased temperature increased water loss higher water needs; may cause death of organisms if temperature too high; rising sea levels (thermal expansion of water) and melting of glaciers and polar icecaps may also impact on ecosystems

• Decreased rainfall reduced water availability decreased biomass (less plants less animals)

• Reduced water table dries out seasonal water sources (eg swamps, small creeks) and cave systems, less water decreased biomass (less plants less animals)

• Change in seasons organisms may not be able to find enough food to survive & raise offspring eg birds breed as light levels change, insects breed as temperature rises