Characterizing Populations and Reproduction Strategies
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Population
All members of a single species living in a specific area at the same time
population size
Number of individuals
Population Density
Number of individuals living in a given area (Individuals/area^2) Random, Uniform, Clustered
Birthrate or natality
Number of live births added annually per 1000 individuals Crude Birth Rate = (No. of live births in a year/Population size) x 1000
Deathrate or mortality
Number of deaths added annually per 1000 individuals Crude Death Rate = (No. of deaths in a year/Population size) x 1000
natural Growth rate
(%) = Birthrate - Deathrate
Doubling time
(Years) = 70/Growth rate (%)
Immigration
Movement of individuals into a population
Emigration
Movement of individuals out of a population
Total growth rate (%)
Total growth rate (%) = (crude Birthrate + immigration) - (crude death rate + emigration)
Calculating population size using growth rate
P(t) = P(0)e^rt P(t) = Population at the time t P(0) = initial population at time 0 e = eulers number r = growth rate t = length of time
Sex ratio
Number of males with respect to number of females Number of males/number of females = Sex Ratio
Age distribution
• Pre-reproductive juveniles • Reproductive adults • Post-reproductive adults
Types of growth
Exponential (J-curve) Logistic (S-curve)
Exponential Growth Rate
An increase in individuals per unit of time “Growth with no limit” dN/dt = rN N = number of individuals r = rate of growth
Carrying Capacity
The maximum population size of a biological species that can be sustained by that specific environment
Logistic Growth Rate
Changes in growth over time Growth slows when approaching carrying capacity dN/dt = rN((K - N)/K) N = number of individuals r = rate of growth K = carrying capacity
Limiting Factors
Factors that prevent the further increase of the population Determine an ecosystem’s carrying capacity
Environmental Resistance
The totality of all limiting factors
Factors affecting growth
Density-dependent factors 1. External Factors 2. Internal Fators Density-independent factors
External Factors
habitat quality, food availability, interactions
Internal Factors
Slow growth and maturity, body size, metabolism, hormonal status
Density-dependent factors
Effect intensifies with increase in population size
Density-independent population factors
Population affected no matter what size (often abiotic) Such as climate extremes, seasonal cycles, pollutants in the environment, fires