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Published byHarold Nelson Modified over 9 years ago
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Populations
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Estimating Abundance
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Population Size Estimating population size –Indices –Density
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Relative Abundance
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Indices for Relative Abundance An index of abundance is a measure that varies directly with the abundance of the population of interest. Based on: Scats, pellets, pellet groups Point or transect counts (Bird Songs) Tracks Signs Etc.
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Index of Deer abundance in Nova Scotia Based on counting pellet groups –Pellet Group Index PGI Pellet groups are counted along a 1 km transect that are within 1 m on either side of the transect. Counting takes place in the spring
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2 m 1 km long PGI = 7 This index can be turned into a density estimate
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Deer Density Index can be converted to a density estimate Need to know how long a period the pellet groups have accumulated over Need to know how often deer defecate per day.
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Birds Point count Line transect count Strip count Variable distance line transect
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Direct Density Estimates
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Catch-effort Methods Assumptions: 1 – The population is closed 2 – Probability of each individual being caught in a trap is constant throughout the experiment 3 – All individuals have the same probability of being caught in sample i
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Catch per unit effort Accumulated catch Number of individuals Leslie plot of catch-effort data
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Capture-Mark-Recapture Techniques For Closed Populations: Single marking, single recapture – Petersen Method Multiple markings and recaptures – Schnabel Method For Open populations: Multiple capture and recapture - Jolly-Seber method
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How do we know that a population is decreasing and in need of protection? Long-term monitoring! Increase or decrease ?
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Survey Data
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Important concepts Habitat movement (dispersal)
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Habitat habitat – physical condition where species live – defined specifically for individual species. source/sink
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Movement Movement (Dispersal) is central to population health! - Density - Genetics What factors affect movement?
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Habitat Reduction and Fragmentation
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Corridors Connectivity
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Spatially structured populations
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High dispersal rate = homogeneous populations, low extinction
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Spatially structured populations Low dispersal rate = heterogeneous populations, high extinction
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Metapopulation Dispersal rate intermediate where individual populations go temporarily extinct.
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Concepts Minimum Viable Population (MVP) Population Viability Analysis (PVA)
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PVA for Spotted Owl
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