ENVIRON 102 Chapter Notes - Chapter 6: Overgrazing, Trophic Level, Limiting Factor
10 May 2018
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Chapter 6 Reading Notes
Ecological Communities
6.1 Competition for Shared Resources
Ecological community: species that interact within a specific area
Intraspecific competition: members of the same species pursue limited resources
Interspecific competition: different species as they compete for shared resources
1930s: G. F. Guase grew two species of single-celled Paramecium – P. aurelia and P. caudatum
o Separately and together
o Increased rapidly in population when grown alone
o Increased slowly when grown together and P. aurelia eventually displaced P. caudatum
o Competitive exclusion principle
Ecologist G. Evelyn Hutchinson suggested concept of ecological niche
o Each organism has a fundamental niche
▪ Fundamental niche: complete range of environmental conditions over which a
species might possible exist
▪ Species with overlapping fundamental niches are potential competitors they
often divide the fundamental niche (division of resources called niche
differentiation)
• Ex: Five species of warblers in New England feed on same food but feed in
different sections of the forest canopy
• Ex: Diverse grasses and herbs in native prairies take up same space and
resources but exploit different portions of the soil in terms of root systems
o Species usually occur in the realized niche; few species actually occur in all parts of the
fundamental niche
▪ Realized niche: range of conditions where a species actually occurs given the
constraints of competition
Organisms compete through exploitation and interference
o Exploitation competition: successful competitors are able to take up resources more
efficiently
o Growth rate of population per unit of limiting resource is higher
o Interference competition: fending off would-be competitors with aggressive/territorial
behavior (scavengers) or releasing chemicals that slow the growth of competitors (plants
and microbes)
6.2 Herbivory, Predation, and Parasitism
Herbivores eat plants; predators hunt/kill/eat animals; parasites live on other organisms
HERBIVORES
Fructivores eat fruits
Gramnivores eat seeds
They obtain energy for themselves while also aiding in sexual reproduction (helping pollinate the
plants) and ensuring genetic diversity
Grazers do not kill plants but slow the growth
o Basic of chemistry of plants is a challenge to grazing animals
o Cellulose (polymer of sugar glucose) make up plant leaves and stem
o Chemical bonds in cellulose are resistant to digestive enzymes
o Ungulates: cloven-hoofed herbivores that have microorganisms in their multi-chambered
stomachs that produce an enzyme that can digest cellulose (ex: goats and cattle)
Plant defense against herbivores (thorns, toxic chemicals, irritating hairs) + herbivore adaptation
to plant defense adaptations example of coevolution
find more resources at oneclass.com
find more resources at oneclass.com
Coevolution: evolution of both predator and prey
o Ex: milkweed plants and monarch butterflies – milkweed produces alkaloids that are
usually toxic to most animals but monarch butterfly caterpillars can tolerate the alkaloids
and store it in their tissues
Herbivore population limited by predation
PREDATORS
Two feeding strategies: filtering feeding and hunting
Filter feeding – using webs or netlike structures to trap prey
o Ex: spiders, marine shrimp, blue whale
Hunting – actively stalking and capturing their prey
o Natural selection favors predators with keen senses of sight and smell
o Coevolution of predator and prey
o Evolution of prey in defense of predator
Population of predators limited by population of prey and vice versa
o Population-prey population cycles
Prey switching occurs when predators deplete a prey species and then switch to a more
abundant prey species
o Ensures that none of the prey species is totally eliminated
Predation increases overall health of the prey population – picks out youngest, oldest, or sickest
o Ex: white-tailed deer absence of natural predators spread of chronic disease
PARASITES
Live in/on and feed on hosts
Doesn’t immediately kill host, but may harm host and may eventually kill host
Vectors: carriers of a parasite but is not affected by the parasite
Spread of parasitic disease governed by four factors:
o Abundance of hosts
▪ The more hosts, the more parasites (ex: bubonic plague in 14th century Europe)
o Accessibility of hosts
▪ The more ecological diversity, the more difficult for parasites to find a new host
o Transmission of hosts
▪ Rate of transmission
▪ Ex: fungus that caused the chestnut blight vs. fungus that cause elm disease
o Length of life of an infected host
▪ Longer in the host, the more opportunity for transmission
6.3 Mutualism and Commensalism
Symbioses: intimate interdependencies
Mutualism: relationship between two species in which they both benefit
Pollination systems – pollinators receive source of food (nectar or pollen); plants are ensured
breeding success and genetic diversity
Loose systems vs. tight systems
o Loose system = several species of pollinators per plant
o Tight system = one species of pollinator per plant
Acacia ants and bull-horn acacia trees in dry tropical forests of Central America
o Bull-horn acacia trees have thorns that acacia ants nest in and leaves and nectar the ants
feed on
o Ants ward off herbivores that potentially defoliate the plant
Result of coevolution
Plays a role in global cycling of nitrogen
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Ecological community: species that interact within a specific area. Intraspecific competition: members of the same species pursue limited resources. Interspecific competition: different species as they compete for shared resources. Herbivores eat plants; predators hunt/kill/eat animals; parasites live on other organisms. They obtain energy for themselves while also aiding in sexual reproduction (helping pollinate the plants) and ensuring genetic diversity. Plant defense against herbivores (thorns, toxic chemicals, irritating hairs) + herbivore adaptation to plant defense adaptations example of coevolution. Two feeding strategies: filtering feeding and hunting. Filter feeding using webs or netlike structures to trap prey. Hunting actively stalking and capturing their prey: ex: spiders, marine shrimp, blue whale, natural selection favors predators with keen senses of sight and smell, coevolution of predator and prey, evolution of prey in defense of predator. Population of predators limited by population of prey and vice versa: population-prey population cycles. Prey switching occurs when predators deplete a prey species and then switch to a more.
