Warm up: Mark-recapture method You are trying to determine the number of individual seagulls in a population at Oceanside Harbor. You initially capture 25 seagulls and tag their feet with a non- invasive bracelet. 1 week later, you capture a new batch of seagulls. Of the 50 that you captured on this second outing, 10 of them were marked with your bracelet. Estimate the population size of the seagulls at Oceanside Harbor. N = (MC)/R N = [(25)(50)]/10 N = 125 seagulls

What you need to know! The differences between exponential and logistic models of population growth How density-dependent and density-independent factors can control population growth

Population Growth The rate at which a population increases or decreases G = growth rate of a population (# of individuals added per unit time) N = population size (at a given time) r = intrinsic rate of increase (maximum capacity of members of that population to reproduce) The average contribution of each individual to population growth r = (births – deaths)/N in a time period K = carrying capacity (maximum population size an environment can support)

Practice A pod of dolphins has 100 members. In a single reproductive cycle there are 50 births and 30 deaths. What is the net increase per individual (r) in one reproductive cycle?

Exponential Growth Model Rate of population growth under ideal conditions The whole population is reproducing in each time interval G = rN

Logistic Growth Model Populations cannot increase indefinitely Limiting factors will restrict population growth Carrying capacity is the maximum population size an environment can support G = rN[(K-N)/K]

Practice If a pod of dolphins has 150 members (N) and an intrinsic rate of increase of .2 (r), then what is the growth rate (G) in ideal conditions (G = rN) in a single reproductive cycle? If that same pod of dolphins is in an environment that can only support 200 dolphins (K), then what is G in a single reproductive cycle?

Limiting Factors Anything that reduces population growth Density-dependent factors apply as populations increase in size: Competition: food, water, territory, etc. Health (disease, waste) Physiological factors: stress triggered transformations Density-independent (abiotic) factors apply to all populations, regardless of size Weather Climate change Natural disasters

Boom-and-Bust Some species have very specific patterns of growth followed by rapid decline Lemmings and Snowshoe hare both exhibit this pattern Several hypothesis exist for why the populations bust, but no one knows for certain Lynx hunt Snowshoe hare almost exclusively and show the same boom-and-bust pattern Predator prey interdependence

Additional Population Growth Problems The population of a colony of bacteria is 500. If there are no limiting factors on the population growth and the intrinsic rate of increase is 0.4, what is the growth rate (G) in a single reproductive cycle? Which growth model does this population fall under? The population of deer in a forest is 300. If the carrying capacity of the forest is 325 and the intrinsic rate of increase is .2, what is the growth rate (G) in a single reproductive cycle? Which growth model does this population fall under?