ECOLOGY
Ecology: the study of interactions of organisms with their environments.
Levels of ecological complexity:
Organisms: how does the organism adapt to meet the challenges put forth by
the environments?
Population: an interbreeding group of individuals belonging to same e species
that, living in a particular geographic area, using common resources, and
regulated by same natural phenomenon ( tempr, water, food, predation)
Community: all the organisms that inhabit a particular area and interact
together
Ecosystem: all the life forms existing in an area in addition to all the nonliving factors
Biosphere: global ecosystem, the most complex level in ecology. a self
contained area that includes the atmosphere up to several km, the land down
to 1500m deep, lakes, caves and the ocean.
All interactions are two ways: organisms affect their environment by their
presence and activities, and organisms are affected by their environment.
Environmental factors:
 Abiotic: non living factors: tempr, water, weather events, wind, soil
structure, nutrients, chemicals, soil pH, sunlight, fire
 Biotic: living factors; other organisms plants, animals, fungi, bacteria,
protists, prey, predators, competitors.
Habitat: environmental situation in which organisms live. aquatic habitat
conditions salinity, tempr, depth, oxygen. Terrestrial habitat conditions,
tempr, humidity, water availability, seasonal variations.
Community Structure:
A community has 4 defining characteristics:
1. biodiversity: variety of different kinds of organisms that comprise it.
This is dependent on:
a. species richness: the total number of different species in a
community
b. relative abundance: abundance of each type of species
compared to one another in a community
2. Prevalent form of vegetation:
a. What plants are present?
b. What plants are dominant?
c. How are the plants structured?
The type of vegetation influences and determines the kinds of animals found
in the community because of nest spaces, shelter, food…
3. Stability: the community’s ability to resist change and return to its
original species composition following disturbances.
a. Forest vs., grassland
b. Ecological succession
1. primary succession: nothing has grown before
2. secondary succession: growth following disturbances
4. Trophic levels: feeding relationships among the various species making
up the community. Decomposers, Producers, Herbivores, Carnivores,
Omnivores.
Niche: A population's role in its community, the way it uses the resources of
its habitat. EX; canopy dweller, ground dweller, fruit eater, leaf eater,
carnivore, herbivore.
Competition: occurs when 2 or more organisms require the same limiting
resource. Two types of competition
- Intraspecific competition: competition within a population for the
same resource
- Interspecific competition: competition between individuals of 2
species for the same resource
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Competitive exclusion principle: two species compete for the
same resource cannot coexist and one will be eliminated
Resource partitioning: when the competing species share a
resource so that each species utilizes the resource differently.
may prevent elimination of one species.
Predation: an interaction in which one species eats another. Predator: the
consumer: prey: the food
Predation may keep both prey and predator under control. Increase in prey
population --->increases predator population -----> decrease in prey pop.---->
decrease in predator population -----> increase in prey population.
Predation helps controls many population density and helps maintain species
diversity.
Anti predator defenses: prey evolve to avoid predation
 Thorns, spines, stingers
 Noxious chemicals and poisons ( plants and animals). Animals
have bright colors to warn predators. Plants use flavor
chemicals
 Camouflage to blend with background or environment
 Mimicry a defenseless potential prey mimics an animal with
antipredator defenses that predators usually avoid
 Flash patterns
Coevolution: a series of reciprocal adaptations in prey and predator species.
Many prey species evolve antipredator defense mechanisms.
 Armor, spines
 Noxious chemicals
 Grow out of predator's reach
Predator responds by:
 tough mouth tissues, sharp teeth
 special enzymes to digest chemicals
 Grow to reach the prey
Symbiosis: an interaction between two or more species in which one species
lives in or on another.
 Parasitism: parasite derives its food from the host and the host
suffers but may not be killed quickly.
 Commensalism: one partner benefits, the other is not really
affected
 Mutualism: both partners benefit from the relationship.
Disturbances: Are events like storms, floods, fire, human activities that
damage a community and change the resources. Most communities have a
tendency to remain in a balance due to the interactions of organisms.
However, disturbances like fire and floods can occur and can change and
restructure a community.
- We think of disturbances as negative usually.
- Sometimes, small disturbances can have a positive impact
- Communities change enormously after major events and are gradually
replaced by a succession of species.
Primary succession: when a community develops in a lifeless area with no soil.
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Example a volcanic island or an area made by a glacier
Initially, autotrophic microorganisms grow.
Then spores of mosses and lichens are brought by wind and initiate
the earliest heterotrophic forms of life
Soil is made from decomposed organisms
Plants start sprouting and growing forming the prevalent form of
vegetation
May take hundreds or thousands of years
Secondary Succession: when a disturbance has destroyed an existing
community but the soil is unharmed.
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Usually earliest plants are herbaceous with no wood
Slowly woody shrubs appear and are followed by trees
Humans are the most important reason for disturbances
Eventually, the community will go back to what it was before
destruction