Chapter 50An Introduction to Ecology and

The Biosphere

I.  Scope of ecology            A.  Interactions between organisms and their environment                        1.  Ecology is the scientific study of the interactions between organisms and their environment.                                      a.  Interactions determine distribution and abundance of organisms. b.  Two main themes in ecology are:              - Where do organisms live? & Why?              - How many organisms are present? & Why? 

                                   c.  Ecology was historically an observational science, often descriptive natural history. d.  An organism’s environment has both abiotic and biotic components.                                                - Abiotic components are nonliving chemical and physical factors such as temperature, light, water, and nutrients.                                                - Biotic components are living factors such as other organisms.

2.  Ecology and evolutionary biology are closely related sciences                                    a.  Events that occur in the framework of ecological time (minutes, days, years) translate into effects over evolutionary time (decades, millennia).                                                Example:  Hawks feeding on mice impact mouse population and may eventually lead to selection for mice with fur as camouflage.

3.  Ecological research scale ranges from individuals to the biosphere                                    a.  Organismal ecology is concerned about the way in which an individual interacts with its environment. b.  Population ecology is the study of a group of individuals of the same species. c.  Community ecology deals with all interacting species within a particular area.

                                    d.  An ecosystem consists of all abiotic factors plus all organisms that exist in a certain area Ecosystem ecology. Landscape ecology- interactions among ecosystems.

e.  The biosphere is the global ecosystem.  Global climate research is an example of ecology at the biosphere scale. 

II.  Factors affecting the distribution of organisms            - Biogeography is the study of past and present distribution of individual species.   

A.  Species dispersal contributes to the distribution of organisms                        Dispersal refers to the process of distribution of individuals within geographic population boundaries.  Question: Is the distribution of a species limited by dispersal, i.e. by movement of the organisms?

Answer can be obtained by transplant experiments.

If the transplant is successful, then the organisms just haven’t reached the target area. If the transplant is not successful, then other factors limit the distribution of the organisms, such as competitors, lack of a food source, etc.

a.  Introduced species sometimes have disasterous impacts:

           - African honeybee, Zebra mussels

Many introductions intentional.

The “Laws of 10”.

Why do the successful invaders succeed?

Invasional meltdowns?

Climate change effects?

            B.  Behavior and habitat selection contribute to the distribution of organisms                        1.  Organisms may not occupy all potentially suitable habitat.  Why?            a.  Evolution doesn’t lead to perfect organisms.  b.  Evolution is an ongoing process.  Environments change, but it takes a while for organisms to respond. 

            C.  Biotic factors affect distribution                        1.  Organisms required for potential community members to colonize may be lacking.           - Pollinators, prey, predators that limit competition 

D.  Abiotic factors affect distribution                        1.  Abiotic factors of interest include:                                   

- Temperature (range from 0 to 45 C)                                    - Water                                    - Sunlight                                    - Wind (increases heat & water loss)                                    - Rocks and soil

Fig. 50.13

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• Local and seasonal effects on climate.– Bodies of water and topographic features such as

mountain ranges can affect local climates.– Ocean currents can influence climate in coastal

areas.– Mountains affect rainfall greatly.

Fig. 50.14

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

                                   

b.  Lake stratification and mixing alters oxygen and nutrient levels. Dependent on temperature changes and effect on water density. 

Aquatic and terrestrial biomes

(Biome = major ecosystem type)

 A.  Aquatic biomes cover about 75% of the earth’s surface

                        - Wetlands

                        - Lakes

                        - Rivers, streams

                        - Intertidal zones

                        - Oceanic pelagic biome

                        - Coral reefs

                        - Benthos

 

                 

Oligotrophic Lake: Nutrient poor, water is clear, oxygen rich; little productivity by algae, relatively deep with little surface area.

Eutrophic lake: nutrient rich, lots of algal productivity so it’s oxygen poor at times, water is murkier often a result of input of agricultural fertilizers

Rivers and Streams: Organisms need adaptations so that they are not swept away by moving water; heavily affected by man changing the course of flow (E.g. dams and channel-straightening) and by using rivers to dispose of waste.

Wetlands: includes marshes, bogs, swamps, seasonal ponds. Among richest biomes with respect to biodiversity and productivity. Very few now exist as they are thought of often as wastelands.

Estuary: Place where freshwater stream or river merges with the ocean. Highly productive biome; important for fisheries and feeding places for water fowl. Often heavily polluted from river input so many fisheries are now lost.

Marine environment with zonation.

Intertidal Zone: Alternately submerged and exposed by daily cycle of tides. Often polluted by oil that decreases biodiversity.

Coral Reefs: occur in neritic zones of warm, tropical water, dominated by cnidarians (corals); very productive, protect land from storms; most are now dying from rise in global temperatures

Deep-sea vent: Occurs in benthic zone; diverse, unusual organisms; energy comes not from light but from chemicals released from the magma.

B.  Terrestrial biomes                        - Tropical forest                        - Savanna                        - Desert                        - Chaparral                        - Temperate grassland                        - Temperate deciduous forest                        - Coniferous forest                        - Tundra                        

Tropical Forest: Vertical stratification with trees in canopy blocking light to bottom strata. Many trees covered by epiphytes (plants that grow on other plants).

Example of Tropical, Dry Forest

Desert: Sparse rainfall (< 30 cm per year), plants and animals adapted for water storage and conservation. Can be either very, very hot, or very cold (e.g. Antarctica)

Chaparral: Dense, spiny, evergreen shrubs, mild rainy winters; long, hot, dry summers. Periodic fires, some plants require fire for seeds to germinate.

Temperate Grassland: Marked by seasonal drought and fires, and grazing by large animals. Rich habitat for agriculture, very little prairie exists in US today.

Temperate Deciduous Forest: Mid-latitudes with moderate amounts of moisture, distinct vertical strata: trees, understory shrubs, herbaceous sub-stratum. Loss of leaves in cold, many animals hibernate or migrate then. Original forests lost from North America by logging and clearing.

Coniferous forest: Largest terrestial biome on earth, old growth forests rapidly disappearing, usually receives lots of moisture as rain or snow.

Tundra: Permafrost (Permanent frozen ground), bitter cold, high winds and thus no trees. Has 20% of land surface on earth.