Population Ecology

Population Dynamics Population: All the individuals of a species that live together in an area Demography: The statistical study of populations, allows predictions to be made about how a population will change Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

Population Dynamics Three Key Features of Populations Size Density Dispersion Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

Three Key Features of Populations Size: number of individuals in an area Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

Three Key Features of Populations Growth Rate: Birth Rate (natality) - Death Rate (mortality) How many individuals are born vs. how many die Birth rate (b) − death rate (d) = rate of natural increase (r) Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

Three Key Features of Populations Density: measurement of population per unit area or unit volume Pop. Density = # of individuals ÷ unit of space Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

How Do You Affect Density? Immigration: movement of individuals into a population Emigration: movement of individuals out of a population Density-dependent factors: Biotic factors in the environment that have an increasing effect as population size increases (disease, competition, parasites) Density-independent factors: Abiotic factors in the environment that affect populations regardless of their density (temperature, weather)

Factors That Affect Future Population Growth Immigration + + - Population Mortality Birth - Emigration

Population Dispersion

Three Key Features of Populations Dispersion: describes the spacing of organisms relative to each other Clumped Uniform Random Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

How Are Populations Measured? Population density = number of individuals in a given area or volume Count all the individuals in a population Estimate by sampling Mark-Recapture Method

Mark and Recapture Method R (marked recaptured) = M (Marked initially) T (total in second sample) N (total population size) SO we can rearrange this to find total population size N = M x T R

Mark and Recapture Example Suppose you took 200 mice out of a forest having an unknown number of mice, put leg bands on them, return them to the forest and let them mix thoroughly. If you then take 250 mice from the forest and find 50 of them to be have leg bands, what is the total population size?

Example continued… M= 200 T= 250 R= 50 200 x 250 = 1000 mice 50

How Do Populations Grow? Idealized models describe two kinds of population growth: Exponential Growth 2. Logistic Growth

Exponential Growth Curve Figure 35.3A

Logistic Growth Curve

Reproductive Strategies R Strategists Short life span Small body size Reproduce quickly Have many young Little parental care Ex: cockroaches, weeds, bacteria

Reproductive Strategies K Strategists Long life span Large body size Reproduce slowly Have few young Provides parental care Ex: humans, elephants

Human Population Growth Grows at a rate of about 80 million yearly r =1.3% Why doesn’t environmental resistance take effect? Altering their environment Technological advances The cultural revolution The agricultural revolution The industrial-medical revolution

The Human Population Doubled three times in the last three centuries ~ 7.4 billion and may reach 9.3 billion by the year 2050 Improved health and technology have lowered death rates

History of the Human Population