BIOL150 Lecture Notes - Lecture 5: Ecological Niche, Interspecific Competition, Intraspecific Competition
2 May 2018
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• Community Ecology
• A biological community is an assemble is an assemblage of populations of various
species living close enough for potential interaction
• Interspecific interactions
o Competition
o Predation
o Herbivory
o Parasitism
• Interspecific competition (-/-) occurs when species compete for a resource in short
supply
o food, space, light, water
• Intraspecific competition increases with population density - major cause of density
dependent growth
• The total of a species’ use of biotic and abiotic resources is an ecological niche
• Fundamental niche - is the niche potentially occupied by that species
• Realized niche - is the niche actually occupied by that species
• Competitive Exclusion - 2 species with the same niche cannot coexist
o as a result of asymmetric competition: when species a and b have relatively
high fitness but together one has a higher fitness than the other.
• Niche differentiation (i.e resource partitioning) - differentiation of ecological niches,
enabling similar species to coexist in a community without experiencing competitive
exclusion
o Spatial partitioning - lizards of the dominican republic restrict what parts of the
habitat they use when in combination
o Temporal partitioning
▪ The common spiny mouse and the golden spiny mouse show temporal
partitioning of niches
▪ both species are normally nocturnal, but where they coexist the golden
spiny mouse becomes active during the day
• Character displacement is a tendency for characteristics to be more divergent in
sympatric populations of two species than in allopatric populations of the same two
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species
o if 2 species share space they are more likely to diverge in character
o on their own, they are more likely to have the same character
• Consumption: predation, herbivory, parasitism (+/-)
o Herbivores: eats plants
o Predators: eat whole animals
o Parasites: usually small relative to host, not necessarily fatal, consume
relatively small amounts of another individual
o Defensive adaptations
▪ Behavioural: hiding, fleeing, forming herds
▪ Chemical: toxins, venoms
▪ Morphological: spines, hooves
▪ Camouflage: makes prey difficult to spot
o Aposematic coloration: a bright warning of dangerous or or noxious defences
o Batesian mimicry: palatable harmless species mimics an unpalatable or
harmful model
o Mullerian mimicry: two harmful species mimic each other
o Defences to deter consumption can be:
▪ Constitutive: always present
• e.g mimicry, toxins, thorns
• expensive to maintain
▪ Inducible: produced in response to damage or stress
• e.g blue mussel shells thicken because of crabs
• takes time to produce them
▪ Competition, predation, herbivory and parasitism leads to co-
evolutionary arms race
• Co-evolutionary arms race
o Traits that increase feeding efficiency evolve in predators and herbivores
o traits that make prey unpalatable or elusive evolve
▪ e.g humans and most serious human parasite that cause malaria
• Herbivory
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o top-down (predatory) control
o bottom up (nitrogen limitation) control
o plant defences
• Parasitism (+/-)
o parasites that live within the body of their host are called endoparasites
o parasites that live on the external surfaces of a host are ectoparasites
• Mutualism (+/+)
o Can be
▪ Obligate: where one species cannot survive without the other
▪ Facultative: where both species can survive alone
• ants that farms aphids
• Commensalism (+/0)
o e.g water buffalo disturb insects while feeding, cattle or sea egrets take
advantage and have a more available insect supply
• Facilitation (+/+ or +/0)
o is an interaction in which one species has positive effects on another species
without direct and intimate contact (not a symbiotic relationship)
o e.g the black rush makes the soil more hospitable for other plant species
o e.g Juncus, a genus of rush, amends the soil to support a greater diversity of
plants than it would without Juncus present
• Allelopathy - an organism produces one or more biochemicals influence germination,
growth, survival, and reproduction of other organism
• Two fundamental features of community structure are species diversity and feeding
relationships
• Species diversity - variety of organisms that make up the community
o two components: species richness and relative abundance
o species richness - is the number different species in the community (S)
o relative abundance - the proportion each species represents of all individuals
in the community - n/N = p
o Shannon Diversity Index (H)
▪ H = - SUM plnp
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