Populations

What is a population? -a group of actively interacting and interbreeding individuals in space and time.

populations are characterized by: -density, -distribution in space, -age structure, -sex ratio, -birth rate, -death rate, -emigration rate, -immigration rate, -genetic structure. - Selection operates on individuals, populations evolve

Density Dynamics Density change is a function of: Birth rate, immigration rate and Death rate, emigration rate

Population Size Theory of population growth

Population Growth (Density Independence)‏ N t+1 = RN t where N t is the population size at time t and R is the reproductive value -if R=2 then populations increase as 1,2,4,8,16 etc. =2 t rewritten as N t = R t - If R=1 ? If R<1 ?

Life Tables

Life tables Cohort vs Static x - age l x – survivorship m x –age specific fecundity R= net reproductive rate = Σ l x * m x G= generation = Σ x*l x * m x / R Assumes stable age distribution

Lifetable SurvivorshipFecundity xlxmxlxmxx(lxmx) sum(lxmx) =3 Ro=1 Generation time (G) =3.00r m = 0.00 Xage class lxproportion surviving to start of age interval mxfecundity (average number of young per female Roreproductive value Ggeneration time r m = innate capacity for increase

Important concepts Habitat movement (dispersal)‏

Habitat habitat – physical condition where species live – defined specifically for individual species. source/sink

Habitat Reduction and Fragmentation

Movement Movement (Dispersal) is central to population health! - Density - Genetics What factors affect movement?

Corridors Connectivity

Spatially structured populations

High dispersal rate = homogeneous populations, low extinction

Spatially structured populations Low dispersal rate = heterogeneous populations, high extinction

Metapopulation Dispersal rate intermediate where individual populations go temporarily extinct.

Concepts Minimum Viable Population (MVP)‏ Population Viability Analysis (PVA)‏

PVA for Spotted Owl

Estimating Abundance

Population Size Estimating population size –Indices –Density

Relative Abundance

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.

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

2 m 1 km long PGI = 7 This index can be turned into a density estimate

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.

Birds Point count Line transect count Strip count Variable distance line transect

Direct Density Estimates

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

Catch per unit effort Accumulated catch Number of individuals Leslie plot of catch-effort data

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

How do we know that a population is decreasing and in need of protection? Long-term monitoring! Increase or decrease ?

Survey Data