Population Dynamics PDF

Population Dynamics Population: species occupying a defined area during a specific time Every popn has: 1. Size: # of individuals 2. Natality: birth rate 3. Mortality: death rate 4. Sex ratio: # of males to females 5. Age structure: can vary radically→  Recruitment: #...

Population Dynamics Population: species occupying a defined area during a specific time Every popn has: 1. Size: # of individuals 2. Natality: birth rate 3. Mortality: death rate 4. Sex ratio: # of males to females 5. Age structure: can vary radically→  Recruitment: # of new indvls reaching breeding age + immigration Immigration: influx of new indvls into a popn Emigration (dispersal): indvls leaving a popn animals give birth to more indvls than survive to breeding age if deaths didn’t offset births = infinitely growing popns→ Exponential Growth Curve→  Exponential growth rare limiting factors kick in, limit growth ex: starvation, predation, disease→  Sigmoid Growth Curve→ IP  inflection point (IP): point on curve where popn is still growing, but at a slower rate carrying capacity (K): max # of indvls an envt/habitat can sustain K can change over time: variation in envt if K exceeded, growth rate drops→  Density-dependent mortality factor: incurs greater mortality as a popn becomes denser (ex: ?) predation, disease, starvation→  Density-independent mortality factor: incurs greater mortality regardless of popn density (ex: ?) hurricane, flooding, fire, catastrophic events→  Sex Ratio: relative abundance of each sex in a popn % of males and females/100 indvls – 40:60 (2:3) or 50:50 (1:1) mortality factors: male (?) and female (?) Wild Turkeys→  Primary Sex Ratio: at fertilization Secondary Sex Ratio: at birth – nutritional stress in deer favors males Tertiary Sex Ratio: of juveniles – influences future breeding popn – Don’t Take a Jake Rule: turkeys Quaternary Sex Ratio: adults – can be highly skewed, managed→  K-selected: large, long-lived organisms; produce few offspring high level of parental care ex: elephants, whales r-selected: small, short-lived organisms; produce many offspring w/high mortality little parental care ex: rodents, fish, insects, amphibians→  Calculate changes in popn size over time Plot them w/graphs Births and Deaths: r = b - d r = actual increase/decrease of popn b = natality; d = mortality N2 = N1 + (b - d) N = population size i = immigration; e = emigration r = (b - d) + (i - e)→  Additive mortality: accumulation of factors Ex: 100 cottontail rabbits predators kill 40; starvation kills 40 40 + 40 = 80 = additive mortality Un-realistic in nature predators kill 40; reduces strain on food; fewer die from starvation = compensatory mortality Ex: mink-muskrat - (Errington) mink harvest surplus muskrats if remove mink, the same # of muskrats die from other factors (disease)→  Density-dep. factors act in a compensatory manner Density-ind. factors act in an additive manner Hunting usually acts in a compensatory manner; depends on timing of harvest ex: fall and spring quail harvests→  Crude Annual Mortality Rate (a): m = hunting mortality rate n = natural mortality rate If additive: n = 70% and m = 20% 0.70 + 0.20 = 0.90 (90% mortality rate) If compensatory: a = m + n - (mn) 0.70 + 0.20 - (0.70 x 0.20) = 0.76 (76% mortality rate)→  Life Table: describes mortality as it affects various age grps/cohort - handout x = time interval (year) lx = # alive at time x dx = # dying during time x→  Sources of Population Data 1. Census: complete count of indvls in a popn; rarely used – Ex: ? 2. Population estimates: sample of the whole popn (mark-recapture) – survival – Ex: ? 3. Index: quantitative measure of a popn Used frequently; relatively easy – Ex: point counts; nests/unit area→