Population Ecology Ms. Day AP Biology

Population Ecology Population ecology = study of populations in an environment, including environmental influences on density and distribution, age structure, and population size Population = group of same individuals of a single species living in the same general area at the same time and can interbreed

Density and Dispersion Density is the number of individuals per unit area or volume Dispersion/Distribution is the pattern of spacing among individuals within the boundaries of the population Environmental and social factors influence spacing of individuals in a population

Measuring Density Population Density = individuals unit area Unit area= length x width Ex: What is the density of trees in 1 km2 in there are 1000 trees in 50 km2? 1000 trees = 20 trees 50 km2 km2

influenced by social interactions such as territoriality Clumped distribution influenced by resource availability (living in groups increases the effectiveness of hunting, spreads the work of protecting/caring for young) most common Uniform distribution influenced by social interactions such as territoriality Random distribution the position of each individual is independent of other individuals

What kind of dispersion is this?

What kind of dispersion is this?

What kind of dispersion is this?

Measuring Population Density You usually do NOT count organisms Sampling techniques used by ecologists: 1. Quadrats (aka-Random sampling) Count # of species Repeat in several more locations Average results

Measuring Density 2. Indirect Counting- used for organisms that move around Count # of nests, burrows or tracks

Measuring Density 3. Mark and Recapture Trap organisms Mark with tags or dye Capture again and count Total Population = # in 1st capture x # in 2nd capture # of marked animals recaptured

Study of theory and statistics behind population growth and decline Demography Study of theory and statistics behind population growth and decline N = size of the population

Demographic Statistics Birth rate (b)= number of offspring produced per time period Death rate (d) or (m)= number of deaths per time period Sex ratio = proportion of males and females in a population Generation time = time needed for individuals to reach reproductive maturity

Demographic Statistics These statistics together determine the size and growth rate of a given population Population Growth = (Births + immigration) - (deaths + emigration) If birth rates are greater than death rates, population increases If birth rates are less than than death rates, population decreases If birth rates are equal to the death rates, population remains the same

Which age structure pyramid represents: a developing country? Future unemployment problems? Adequate health care needs?

Population Growth and Size Biotic potential = maximum growth rate of a population given unlimited resources/space, and lack of competition or predators Rate varies from species to species Carrying capacity (K)= maximum number of individuals that a population can sustain in a given environment without destroying the habitat

Limiting Factors Control Population Sizes Density-dependent factors come into play when population approaches and/or passes the carrying capacity Food supplies, waste, population- crowding diseases, H2O, mates, predators Density-independent factors have nothing to do with the population size THINK: NATURE Floods, droughts, earthquakes, other natural disasters and weather conditions

Population Growth Ex: yeast, bacteria IN NATURE, NOT LIKELY… Exponential Growth = population grows as if there are no limitations to how large it can get (biotic potential) J-curve A population increases slowly at first (the "lag phase") and then grows increasingly rapidly with time ("log phase”) IN NATURE, NOT LIKELY… Ex: yeast, bacteria

Population Growth (con’t) 2. Logistic Growth = population growth slows to zero and population size tends to stabilize because of environmental resistance (Limiting factors) S-curve Set by carrying capacity Ex: HUMAN POPULATION, ELEPHANTS K

Point of Maximum growth (K/2)

2 types of population growth Number of generations Population size (N) K = 1,500 1,500 2,000 1,000 500 15 10 5 Logistic growth Exponential growth = 1.0N dN dt 1,500 – N

2 Categories of Organismal Growth Organisms can belong to… K-selected populations: a roughly constant size whose members have low reproductive rates. (THINK: “K”onstant growth and “K”are) Offspring require extensive postnatal care Produce few LARGE offspring Long maturation time Long lifespan/low death rate Usually reproduce often throughout lifetime (occurs later in life) Density dependent factors often limit growth Logistic growth pattern Ex: humans, elephants, monkeys HANG ON!!

Or organisms can belong to… r-selected populations experience rapid growth (THINK: really fast growth) Offspring are small Produce large #’s of offspring Offspring mature rapidly Offspring require little postnatal care Short lifespan/high death rate Usually reproduce once throughout lifetime (occurs early in life) Density independent factors often limit growth Exponential growth pattern Ex: bacteria, mice, lizards

Which surviorship curve shows: An r- strategist? Why? An k- strategist? Why?

Predator-Prey Cycling- Population BOOMS and BUSTS! Many populations undergo boom-and- bust cycles Boom-and-bust cycles are influenced by complex interactions between biotic and abiotic factors