Population Ecology Chapter 55

Environmental Challenge Ecology: the study of how organisms interact with one another and their environments. Populations: groups of individuals of the same species in one place

Populations Range: area throughout which a population occurs Most species have limited geographic range Devil’s hole pupfish lives in a single spring in southern Nevada

Range expansion of the cattle egret Populations Humans alter the environment and some species have altered their range in reponse. Range expansion of the cattle egret

Populations Dispersion: how individuals in a population are spread out within their range Random: individuals do not interact strongly with one another. Uniform: behavioral interactions, resource competition Clumped: uneven distribution of resources.

Biotic Potential The rate of growth for a population if every individual survived and reproduced. Under such ideal conditions, a population would have exponential growth

Exponential growth = J-curve

Growth levels off as population approaches carrying capacity b = d Growth levels off as population approaches carrying capacity Exponential growth initially Population Logistic Growth S-Curve Lag phase

Many populations exhibit logistic growth Growth and Limits Many populations exhibit logistic growth

Carrying capacity (K): the maximum number of individuals in a species that an environment can support Determined by the amount of resources available (food, water, nutrients, etc) Results in logistic growth Hunting brings pop to Winter K

Demography and Dynamics Demography: the quantitative study of populations How size changes through time

Population Changes Calculating growth rates: (Births + I) - (Deaths + E) Immigrants (I) - Individuals moving into a population Emigrants (E) - Individuals moving out of a population (exiting)

Limiting Factors: situations that prevent a population from increasing Density-Independent Factors --do not depend on the number of individuals in the population. --Usually abiotic factors such as pollution, weather events and natural disasters

Density-Dependent Factors -become limiting only when population reaches a certain size -strongest when population is large and dense -usually biotic factors such as food, predators, disease, and competition

Sawtooth Curve: Shows periodic fluctuations (rise and fall) of populations. --Can show density-dependant factors at work (predator-prey) --Can show density-independent factors at work (seasonal changes)

-showing seasonal population fluctuations Sawtooth Graph -showing seasonal population fluctuations summer winter

Fluctuations in the number of pupae of four moth species in Germany

North American snowshoe hare 10 year cycle Two factors generate this cycle: Food plants Predators

Reproductive patterns r-strategist: produce many offspring in a short period of time (mice, flies) take advantage of a temporarily abundant resource k-strategist: produce a few offspring that have a better chance of surviving with intense parental care (humans, elephants) Limited resources, pop near carrying capacity

Human Population Growth K-selected life history traits Small brood size Late reproduction High degree of parental care Human populations have grown exponentially Last 300 years birth rate has remained same Death rate has fallen dramatically

Human population growth:. Year. Estimated population. (in millions) Human population growth: Year Estimated population (in millions) 0 A.D. 130 1650 500 1850 1,000 (1 billion) 1930 2,000 1970 4,000 (4 billion) 1998 6000 5/3/10 6,817,237,780 U.S. 309,191,081

A. The graph of human population is a J curve A.The graph of human population is a J curve. It shows exponential growth Agriculture begins Plowing and irrigation Bubonic plague Industrial Revolution

Number of years to add each billion (year) All of Human History (1800) 123 (1930) 33 (1960) 15 (1975) 12 (1987) 12 (1999) 13 (2012) 16 (2028) 26 (2054) Sources: First and second billion: Population Reference Bureau. Third through ninth billion: United Nations, World Population in 2300 (medium scenario), 2003.

What has allowed human populations to grow exponentially. 1. )medicine What has allowed human populations to grow exponentially? 1.)medicine 2.)plenty of food(agriculture) 3.) sanitation * medical advances allow people to live longer and decreases infant mortality (Child death)

What is Earths’ carrying capacity? Unknown J curve will continue until some resource becomes limiting Some countries have exceeded their carrying capacities: China, Ethiopia, Somalia, India

Sex and age distributions show that less developed countries have significantly younger populations than more developed countries. Roughly one-third of the population in less developed countries is under age 15. In many sub-Saharan African countries, this proportion rises to nearly one-half of the population. In contrast, less than one-fifth of the population in more developed countries is under 15. Today there are more than 2 billion young people below age 20 in less developed regions—the age cohort that will soon become the world’s newest group of parents. Young age structures in the less developed countries are due mainly to higher levels of childbearing in recent decades.

World Population Clock Natural Increase per World More Developed Countries Less Developed Countries Less Developed Countries (less China) Year 80,224,198 912,053 79,312,145 71,498,784 Day 219,792 2,499 217,294 195,887 Minute 153 2 151 136 Source: Population Reference Bureau, 2004 World Population Data Sheet.

Human Population Growth Distribution of population growth

Human Population Growth Consumption in the developed world further depletes resources Wealthiest 20% of the world’s population accounts for 86% consumption of resources and produces 53% of CO2 emissions Poorest countries: 20% is responsible for 1.3% consumption and 3% CO2 emissions

Human Population Growth Ecological Footprint: amount of productive land required to support an individual at the standard of living of a particular population through the course of his/her life