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Published byAdele Dixon Modified over 9 years ago
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Populations and Communities
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A group of individuals of the same species, living in a shared space at a specific point in time = Population
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Factors affecting population size birthsdeaths Population Immigration Emigration
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How big is this population? 6 11 6
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Counting populations I - Counting individuals - Counting by sampling: Population size = Average number of individuals per section x Area of section total study area - Counting by recapture %:
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Counting by recapture % d d d d d d # of marked recaptured animals # of captured animals # of marked animals Population size =
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Population density Factors influencing population density: – Access to water and food – Presence of predators – Parasites, diseases Pop. Density = # of individuals Space occupied (area / volume)
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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
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clumped random uniform
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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 organisms Physical or chemical origin Abiotic Biotic
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Limiting factor A factor that limits the growth of a population – Light – Temperature – Water – Food / nutrients –…–…
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Limiting factor Is low temperature limiting growth of vampire bat population? Vampire bat colonies Mean minimal temperature for January > 10°C
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12 m 200 m Distance between nest boxes Density (pairs / ha) pied flycatcher Is nesting space limiting? Providing more nesting spaces increases population density Nesting space was limiting
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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.
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Populations Counting methods Density (number/ area) Distribution (clumped/ random / uniform) Ecological factors – limiting factors Polpulation cycles commuities
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organism population community Communities: A set of populations of different species sharing the same habitat
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Biodiversity The 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
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Same species richness; community 2: species abundance not even Lower biodiversity Biodiversity is high when: number of species high relative abundance of species similar
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Interactions between individuals Competition: Living organisms seek access to the same resource in their habitat. Predation One feeds on the other. Mutualism: Interaction between two species beneficial to both. Commensalism: One organism benefits from relationship while other remains unaffected.
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Competition interspecific intraspecific
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Predation: predator prey prey may or may not die parasite host Parasite lives either on or inside the host. Host is harmed from the interaction.
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mutualism Bee gains food Flower gains fertilization Clown fish gains protection Anemone gains prey (attracted by clown fish)
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Commensalism Bird gains food Human remains unaffected Bird gains protection tree remains unaffected
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