Download Populations, Communities, Ecosystems

Populations, Communities and Ecosystems Chap 19-20
1. Ecology is the study of interactions between organisms and their environment.
2. A Hierarchy of interactions: cells tissues  organs  organism  population  community 
ecosystem. Organismal Ecology – evolutionary adaptations; Population Ecology – concerns mainly with
population density and growth; Community Ecology – populations of different species, deals with
interactions like predation, competition, symbiosis; Ecosystem Ecology – interactions between biotic
and abiotic components, concerns with energy flow and chemical cycling.
3. A population is an interaction between individuals of same species at a place.
4. A community is an interaction between individuals of different species at a place. A Habitat is the place
where the community lives.
5. An ecosystem is an interaction between living = biotic factors = community and nonliving = abiotic
factors at a place.
6. Ecology and environmentalism: Rachel Carson’s book ‘Silent Spring’ highlighted the bad role of use of
insecticide DDT. It showed decline in populations of Pelicans and Bald eagles was due to DDT. America
banned use of DDT and related insecticides and saved the endangered birds.
7. Abiotic factors of the environment include sunlight, Temperature, wind, soil, rock, water (precipitation =
rain, snowfall, dew, hailstorm). The local conditions of abiotic factors vary and form patchiness of
environment to form Habitat = natural surroundings of a species. Different species can live in same
habitat.
8. Disturbances in environment like fires, hurricanes, tornadoes, earthquakes and volcanic eruptions
damage the community at a place. Most of the times community can recolonize and can grow to earlier
stage. This capacity to resist change is Stability of the community. The disturbance leads to succession of
communities called Ecological Succession.
9. Organisms respond to disturbance or change in environment by Physiological response – like long term
response Acclimation, for example living at high altitude organism starts producing more blood cells;
Anatomical response – by undergoing structural change and behavioral response – some animals can
migrate to suitable conditions.
10. Population ecology: Population density is the number of organisms living per unit area (square mile).
Patterns of dispersion can be clumped, uniform or random.
11. Logistic Growth Model – It is S-shaped. It includes fast growth in the middle part but becomes constant
on reaching Carrying Capacity (k) = maximum number of individuals the Habitat at a place can support. It
is called Equilibrial Population. For example Polar bears.
12. Exponential Growth Model – It continues to grow very fast at maximum reproduction rate (r) even
beyond carrying capacity. Soon population faces population crash when the resources are exhausted. It
is J- shaped. It is called Boom and Bust population. It is found in Opportunistic Populations. For example
in wild flowers.
13. Regulation of population growth is done using Density-dependent factors that change birth and death
rates; and Density-independent factors that affect same % of individuals in all densities – these
populations face boom and bust conditions.
14. Human population Growth – In most of developed world population is either slowly growing (USA) or
decreasing (Italy) but increasing very fast in most of the developing world (Afganistan). The age
structure figures help us understand population growth. When it is a fast growing population the base is
broad and narrows to a point = Pyramid shaped (Afganistan). A steady population has base and middle
part equal; and declining population has narrow base than middle.
15.
Life span
climate
Growth curve
Reproduction
Death rate
Body size
Opportunistic life history
short
unpredictable
Exponential = J-shaped, boom-bust
High rate
High, more in early life
Small, many wild flowers
Equilibrial life history
Long
Relatively predictable
Logistic = S-shaped, stable at carrying capacity
Low rate
Low and in late life
Big, polar bear
Communities have different food chains linked by predation. Each level is called a trophic level. These always
start with Autotrophs = producers that use the sunlight to make their food.
Top Carnivore = tertiary consumer, lion
4th trophic level
Carnivore = Secondary consumer, human, cheetah, tiger
3rd trophic level
Herbivore = primary consumer, deer, hare, zebra, antelope
2nd trophic lelvel
Producers = autotrophs, grass, plants
1st trophic level
1. Diversity of community means the different species living in it.
2. Prevalent forms of plants in a community mainly determine the type of animals living in that
community.
3. The dead bodies of each level are degraded into simple chemicals by Decomposers = Detrivores
4. Some animals like earthworms, millipedes and many larvae are Detrivores because these feed on dead
matter.
5. Bacteria, slime molds and fungi are important decomposers
6. The different organisms like grass or plants, deer or antelope, cheetah or tiger present on same trophic
level do not eat each other and are called Competitors.
7. The organisms feeding on different trophic levels like humans are called Omnivores. Humans feed
directly on plants and animals.
8. Food Chain is linear and joined by predation. Grass  Deer  Lion
9. Omnivore feeds at more than one trophic levels – bears, humans
10. Detrivores feed on detritus, a partially decomposed plant or animal part.
11. Food Web has many interconnected food chains. Only food webs exist in nature
12. Interspecific interactions (between organisms of different species) in a community include
Competition, Predation, and Symbiosis. Refer chapter review.
13. Disturbance of Communities, when moderate in severity and occurrence leads to increase in diversity of
species in the community. Disturbance usually leads to Ecological Succession.
14. Ecological Succession is Primary when it starts on bare rock with no soil. It takes hundreds of years to
reach climax community. Disturbances like hurricanes, fires eliminate the community but leave the soil
intact – The Succession is called Secondary, it takes lesser time to reach climax community.
Chapter 20 Ecosystems:
1. Ecosystem Dynamics: Trophic relationships in an ecosystem determine the routes of energy flow and
chemical cycling. Refer review.
2. Energy flow: is unidirectional in the ecosystem. All the time energy must come from Sun  producers
 carnivores  decomposers. All these lose energy as heat in the environment. The heat ultimately is
lost from the biosphere to the space.
3. Most energy is lost in various activities at each trophic level. Only 5-20% (average 10%) energy is
transferred to the next trophic level.
4. Chemical cycling: Plants take CO2 from air and minerals from soil and form Bio-mass. Herbivores feed on
bio-mass of plants and C and minerals transfer to them. Carnivores get them on feeding on herbivores.
Producers and consumers release CO2 into air. Decomposers or Detrivores break the dead bodies of
producers, herbivores and carnivores and release the minerals back to the soil. Burning also releases
back the CO2 into air.
5. Producers: can fix only 1% of light energy falling on them
6. 5 – 20% (10% average) of energy / bio-mass is passed from one trophic level to the next trophic level.
7. Weather shapes ecosystems
8. Latitude and Elevation: Rays of sun fall straight closer to equator (tropics) and distribute heat in lesser
area. In areas closer to poles rays fall oblique and heat up larger area. Temperature falls from 0⁰ to 90⁰
latitude. Elevation from sea level to mountain top also has a similar effect.
9. Circulation of Air: Sunlight heats the air and makes it lighter. It rises and gets colder and falls back to
earth. It creates 3 great pairs of cycles from equator to poles.
10. Rain Shadow Effect: Moist air from pacific rises on west side of mountain range and gets colder. Lower
temperature decrease water holding capacity of air and rain or snow (precipitation) falls.
11. On the eastern side of mountain range air descends and gets warmer. Rise in temperature increases the
water holding capacity of wind. No rain occurs.
12. Biomes: are very large ecosystems easily recognized on earth. For example, desert, tropical forest,
conifer = evergreen forests, grassland, tundra etc. Tropical forests lie around equator and have high
temperature and high rain. Deciduous forests lie midway between equator and poles and have high
temperature and moderate rain. Evergreen forests or Taiga lie closer to poles and have moderate rain
and cold temperature. Tundra is very cold circumpolar desert. Deserts mostly lie around 30⁰ N or 30⁰ S
and have very low rain and high temperatures. Grasslands represent conditions of low rain and
moderate temperature.
13. Aquatic Biomes: usually have upper Photic Zone with sufficient light for photosynthesis and deeper dark
Benthic Zone. Open Sea = Pelagic Zone is rich in Phytoplanktons (microscopic autotrophs like diatoms
and other unicellular algae) in the photic zone. These, along with the sea weeds, are the producers in
the ocean.