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 Natality - 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

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

Logistic Growth Curve

Carrying Capacity Carrying Capacity (k): The maximum population size that can be supported by the available resources There can only be as many organisms as the environmental resources can support 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.

The logistic population growth model and life histories. This model predicts different growth rates for different populations, relative to carrying capacity. Resource availability depends on the situation. The life history traits that natural selection favors may vary with population density and environmental conditions. In K-selection, organisms live and reproduce around K, and are sensitive to population density. In r-selection, organisms exhibit high rates of reproduction and occur in variable environments in which population densities fluctuate well below K. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

K-Selected Species Poor colonizers Slow maturity Long-lived Low fecundity High investment in care for the young Specialist Good competitors

Exponential Growth Curve Figure 35.3A

r-Selected Species Good colonizers Reach sexual maturity rapidly Short-lived High fecundity Low investment in care for the young Generalists Poor competitors

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

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

Introduction Why do all populations eventually stop growing? What environmental factors stop a population from growing? The first step to answering these questions is to examine the effects of increased population density. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Factors Limiting Growth Rate Declining birth rate or increasing death rate are caused by several factors including: Limited food supply The buildup of toxic wastes Increased disease Predation

Density-Dependent Factors limiting resources (e.g., food & shelter) production of toxic wastes infectious diseases predation stress emigration

Density-Independent Factors severe storms and flooding sudden unpredictable severe cold spells earthquakes and volcanoes catastrophic meteorite impacts

Density-dependent factors increase their affect on a population as population density increases. This is a type of negative feedback. Density-independent factors are unrelated to population density, and there is no feedback to slow population growth. Fig. 52.13 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Negative feedback prevents unlimited population growth A variety of factors can cause negative feedback. Resource limitation in crowded populations can stop population growth by reducing reproduction.

Population dynamics reflect a complex interaction of biotic and abiotic influences Carrying capacity can vary. Year-to-year data can be helpful in analyzing population growth.

Some populations fluctuate erratically, based on many factors. Fig. 52.18 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Other populations have regular boom-and-bust cycles. There are populations that fluctuate greatly. A good example involves the lynx and snowshoe hare that cycle on a ten year basis.

“Booms” and “Busts”

Introduction Humans are not exempt from natural processes. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The human population has been growing almost exponentially for three centuries but cannot do so indefinitely The human population increased relatively slowly until about 1650 when the Plague took an untold number of lives. Ever since, human population numbers have doubled twice How might this population increase stop?

POPULATION CYCLES HUMAN POPULATION 1650 - 500,000,000 1850 - ONE BILLION 1930 - TWO BILLION 1975 - FOUR BILLION 2010 – SIX BILLION 2017 - EIGHT BILLION

Human Population Growth J curve 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

Fig. 52.20 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Human Growth Rate 1.15 - 2005

The Demographic Transition. A regional human population can exist in one of 2 configurations. Zero population growth = high birth rates – high death rates. Zero population growth = low birth rates – low death rates. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Age structure is the relative number of individuals of each age. Age structure diagrams can reveal a population’s growth trends, and can point to future social conditions. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Age Distribution Distribution of males and females in each age group of a population Used to predict future population growth