Population Ecology

• populations evolve as natural selection acts on variation
• Population Ecology: how biotic and abiotic factors affect pops
• density: number of individuals per unit area or vol
• Dispersion: within a pops range, local density may vary
• Three different types of dispersion: random, uniform, and clumped
• Clumped: individuals live where conditions are favorable
• Uniform: often results from direct interactions between individuals
• Random: position of each individual is independent of others
• b: birth per capita (rate)
• m: death per capita(rate)
• B: total number of births
• D: total number of deaths
• r: rate of growth
• K: carrying capacity
• N: population size
• R-selected: reproduce a lot but only some survive, low parental care
• K-selected: less offsprings, high parental care, and keep reproducing until they reach carrying capacity(k)
• -r: population declining( more offspring then resources)
• +r: population growing
• N is less that K then population growing and all its resources aren't used
• N greater then K, population declining, resources all used, reached carrying capacity
• Overall changes: B-D
• rate of pop changing over time: r=b-m
• dn/dt=B-D=bN-mN= N(b-m)= rN=
• Exponential growth model: describes population in which conditions are ideal
• Intrinsic rate(rmax): max rate at which population could increase under ideal conditions
• microorganisms have highest rmax
• Large animals tend to have low rmax
• exponential growth characterizes some rebounding populations
• exponential growth model isn't realistic in nature because it cannot continue indefinitely because of environmental resistance and because as density increase there are less resources
• Logistic growth: accounts for environment resistance, as population reaches limit of environment ability to support it, population growth reaches zero
• logistic growth equation: dn/dt=rN x (K-N)/K
• carrying capacity for environment fluctuates
• Organisms that reproduce early in life, put energy towards reproduction and not towards own growth and survival
• Organisms that reproduce late in life, put energy towards growth and survival but decrease time for reproduction
• Semelparous: one single, immense reproductive effort, survival rate is low for adults and offsprings, lots of offspring ensure some will survive
• Iteroparous : reproduce many times, adults survive and reproduce again, competition for resources, few will suited offspring will survive
• Density independent: environment, abiotic elements, r-selection (birth and death rate don't change with density)
• Density dependent: biotic factors, k-selection. As population density increases factors decrease pop growth and as population density decreases factor increase pop growth