ENVIRON 102 Lecture Notes - Lecture 6: Chestnut Blight, Hermit Crab, Ecological Niche
4 May 2018
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February 5, 2015 Lecture Notes
Populations, Communities, and Ecosystems
I. Interspecies (community) interactions and population growth
What’s wrong with the logistic modeling of population growth?
Presumes very tight coupling feedback between resource change and birth rates and death
rates
Presumes that resource needs per individual are constant – that carrying capacity can be equated
to some particular number of individuals
o Is K a fixed number or a relationship?
Populations may be regulated by factors other than limiting resources including
o Retarding factors (e.g. toxin and antibiotics)
o Other organisms (competitors, predators, and parasites)
COMPETITION & the ECOLOGICAL NICHE
G.F. Gause – competitive exclusion is when two organisms vying for the same resource cannot
coexist indefinitely – one will eventually exclude the other
Species coexistence – occurs when multiple species coexist at a ratio of population sizes, or stable
equilibrium
Fundamental ecological niche: the potential range of conditions and resources over which a
species can maintain positive population growth (its range of tolerance for all the factors that it
responds to) = in principle
Realized ecological niche: within its range of tolerance, the actual range over which an organism
occurs taking into account the effects of other organisms = what really happens with the
limitations
Variability in habitats allows variability of niches biodiversity increases because species are
allowed to specialize
Interference competition: prevent competitor from exploiting resources (direct)
Exploitation competition: more effectively use a limiting resource (indirect)
SPECIES INTERACTION AND EVOLUTION
Type of interaction, effect on species 1, effect on species 2
Mutualism, +, +
o Ex: Birds and capsaicin plants
Commensalism, +, 0
o Ex: Hermit crab uses the shell of a dead snail
Predation/parasitism/herbivory, +, –
o Ex: Walnut tree kills other plants around it to use the resources
Neutralism, 0, 0
Amensalism, –, 0
o Ex: Poison ivy and humans
Competition, –, –
Why would chili peppers produce capsaicin?
Capsaicin: molecule in hot peppers that gives you the burning sensation
Repels animals like deer and squirrels
Birds do not sense burning sensation of capsaicin and can spread the seeds in the process
Invasive species and competition
Instances of competitive exclusion
Chestnut tree were wiped out by the chestnut blight in North America
o 7 species of moth that only lived on these chestnut trees also went extinct
Kudzu was introduced to the US to prevent erosion and provide foliage for cattle
o Wipes out other plants by preventing sunlight to pass through
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Populations, communities, and ecosystems rates: is k a fixed number or a relationship? to some particular number of individuals, interspecies (community) interactions and population growth. Populations may be regulated by factors other than limiting resources including. Presumes very tight (cid:498)coupling(cid:499) (cid:523)feedback(cid:524) between resource change and birth rates and death. Presumes that resource needs per individual are constant that carrying capacity can be equated. G. f. gause competitive exclusion is when two organisms vying for the same resource cannot coexist indefinitely one will eventually exclude the other. Species coexistence occurs when multiple species coexist at a ratio of population sizes, or stable: retarding factors (e. g. toxin and antibiotics, other organisms (competitors, predators, and parasites) Fundamental ecological niche: the potential range of conditions and resources over which a equilibrium. Competition & the ecological niche species can maintain positive population growth (its range of tolerance for all the factors that it responds to) = in principle.
