Populations and Communities
• A group of individuals of the same species, living in a shared space at a specific point in time
= Population
Factors affecting population size
births deaths
Population
Immigration Emigration
• How big is this population?
6
11
6
Counting populations I
- Counting individuals
- Counting by sampling:
Population size =
Average number of individuals per section
xArea of section
total study area
- Counting by recapture %:
Counting by recapture %
d
d
d
# of marked recaptured animals# of captured animals
# of marked animalsPopulation size
=
Population density
• Factors influencing population density:– Access to water and food– Presence of predators– Parasites, diseases
Pop. Density =# of individuals
Space occupied (area / volume)
Population distribution
= the way in which individuals are dispersed
within their habitat
clumped
random
uniform
http://www.youtube.com/watch?v=1yKxUNP_XVo&list=PL9CE54703E2B8E92F
clumpedrandom
uniform
Ecological factors
= aspect of a habitat that can affect the organisms living there
• amount of light• soil / water pH• terrain• temperature• air humidity
• birth rate• disease• amount of food• predation• competition• human activity
Related to the action of living
organismsPhysical or
chemical origin
Abiotic Biotic
Limiting factor• A factor that limits the growth of a population– Light– Temperature– Water– Food / nutrients– …
Limiting factor• Is low temperature limiting growth of vampire
bat population?
• Vampire bat colonies
Mean minimal temperature for January > 10°C
12 m200 mDistance between nest boxes
Dens
ity (p
airs
/ ha
)
pied flycatcher
Is nesting space limiting?
Providing more nesting spaces increases population density
Nesting space was limiting
Biological cycles in populations
• Population cycles are composed of alternating rise and fall of population size.
• Periods are of fixed duration and are repeated continually.
Populations
• Counting methods• Density (number/ area)• Distribution (clumped/ random / uniform)• Ecological factors – limiting factors
Polpulation cycles
commuities
organism
populationcommunity
Communities: A set of populations of different species sharing the same habitat
BiodiversityThe variety of species living in a community
Species richness:Number of different species in a community
Relative species abundance:Number of individuals of one species in relation to total community
Same species richness;
community 2: species abundance not even
Lower biodiversity
Biodiversity is high when:• number of species high• relative abundance of species similar
Interactions between individualsCompetition:Living organisms seek access to the same resource in their habitat.
PredationOne feeds on the other.
Mutualism:Interaction between two species beneficial to both.
Commensalism:One organism benefits from relationship while other remains unaffected.
Competition
interspecific
intraspecific
Predation:
predator prey
prey may or may not die
parasite hostParasite lives either on or inside the host. Host is harmed from the interaction.
mutualism
Bee gains foodFlower gains fertilization
Clown fish gains protectionAnemone gains prey (attracted by clown fish)
Commensalism
Bird gains foodHuman remains unaffected
Bird gains protectiontree remains unaffected
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