ECOLOGY chapter 50

Ecology: Study of interactions between organisms and their environment.

Environment includes both abiotic (non-living) and biotic (living) components.

Abiotic: light, water, nutrients, chemicals, rocks, weather, etc.

Biotic: organisms.

Organisms compete with, parasitize, eat or are eaten by and change the environment for other organisms.

Ecology explores a wide range of questions about what factors control the distribution, abundance and behavior of organisms.

For example, Red Kangaroos occur primarily in the Australian interior in semiarid regions.

Distribution of Kangaroos suggests an abiotic factor (precipitation) influences it, but perhaps populations also influenced indirectly by biotic factors such as competitors, predators, food availability and parasites.

Ecologists have to consider multiple factors to explain patterns of abundance and distribution.

Ecology has many subfields of study ranging from ecology of individual organisms to dynamics of landscapesOrganismal EcologyPopulation EcologyCommunity EcologyEcosystem EcologyLandscape EcologyWe will explore these sequentially

Distribution of species

Biogeography: study of the broad patterns of distribution of organisms across the globe.

Patterns strongly influenced by historical factors such as continental drift (see chapter 26) and barriers including mountain ranges and seas.

For example, Australia populated by marsupial mammals (e.g. kangaroos, wombats, koalas) because placental mammals did not colonize it before it separated from other landmasses.

Tapirs found only in southeast Asia and South America. Ancestral populations separated when land masses diverged.

Role of dispersal in distribution

Ability to cross barriers affects distribution.

Thus, species of birds often more widely distributed than mammals.

However, inability to reach an area not only factor that limits distribution. Ability to survive in new area is critical.

To survive and thrive species must be able to cope with both biotic and abiotic factors.

Biotic factors

The presence of competitors or predators may limit an organisms ability to establish itself.

For example, algae are eaten by sea urchins and limpets, which limits the ability of seaweeds to establish themselves on rocks

Biotic factors

Conversely, absence of predators and competitors has allowed many organisms introduced into new areas to increase so much they become pests.

E.g. Japanese beetles (from Asia), zebra mussels and purple loosestrife from Europe) (Melaleuca (Eucalyptus trees from Australia) and many other invasive species have spread widely in the U.S.

Abiotic factors

The major factor affecting distribution of terrestrial organisms is climate, which incorporates temperature, sunlight, wind and precipitation.

Abiotic factors

Climate is determined by global factors such as inputs of solar energy and the movement of the earth through space.

Study discussion of climate patterns pages 1088 and 1089

Climate

Local factors such as the presence of mountains and large bodies of water also affect climate.

Mountains force up moist air moving across them. As the air cools the water condenses and falls as rain. The result is that one side of the mountain range is wet and the other side is drier (and perhaps a desert [e.g. Mojave and Gobi Deserts.])

Climate

Large bodies of water moderate climate. Land heats faster than water and warm air rises. Cooler air over water moves in and replaces the warm air. The warm air that was over land cools at high altitude and sinks over water.Results is steady flow of cool air over land.

Terrestrial Biomes

Biomes are major types of ecosystems that cover large areas of the earth and are classified by their dominant vegetation types.

(an ecosystem is the community of organisms in an area and their physical environment)

Each biome also is populated by a diverse array of animals, fungi and microorganisms adapted to that environment.

Major terrestrial biomes include

Tropical forest

Desert

Temperate Grassland

Savanna

Temperate broadleaf forest

Coniferous forest (Taiga)

Tundra

(see descriptions pages 1100-1104)

Savannah

Terrestrial biomes

Terrestrial biomes often vertically stratified. Layers defined by different size plants

(e.g. in forests there is an upper canopy of tall trees, low tree layer, shrub layer, ground layer of herbaceous plants, litter layer and root zone).

Stratification provides multiple different habitats for animals which occupy specialized feeding niches.

Convergent evolution

Actual species in a biome differ from one area to another but they possess similar adaptations.

This is convergent evolution (development of same evolutionary solutions to ecological problems)

Convergent evolution

For example vegetation in all deserts worldwide characterized by extensive root systems, long-term water storage capability, thick waxy coverings to reduce water loss, and extremely small (if any) leaves

Biomes often maintained by disturbance.

Wildfires are an essential factor in maintaining many biomes (e.g. grasslands, savannahs, some coniferous forests). Fire favors trees such as longleaf pine whose bark resists fire and grasses, which recover quickly after burning.

Aquatic biomes

Aquatic biomes less influenced by climate than terrestrial biomes

Why?

Aquatic biomes

Water is more thermally stable.

It takes a lot of heat to change the temperature of a body of water.

Major aquatic biomesLakesRiversEstuariesIntertidal zoneMarine pelagic zoneCoral reefsMarine benthic zone (benthic zone is sea/lakefloor)See pages 1094-1097.

Aquatic biomes often stratified by light and temperature.

Light intensity decreases with depth. Upper (photic) zone supports photosynthesis.

In ocean photic zone narrow but contains most organisms.

Aphotic zone sparsely populated.

Benthic zone (bottom) organisms often depend on rain of dead organic matter (detritus) from above.

Thermal stratification of lakes

In temperate areas lakes are thermally stratified in summer and winter.

Water densest at 4ºC so water at this temperature sinks through colder or warmer water.

Thus, in spring and fall all water in lake mixes which redistributes nutrients throughout the lake.