1 Population Ecology Chapter 55

2 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

3 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

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

6 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 – “Territorial” –Clumped: uneven distribution of resources.

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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

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

11 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

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(Non-Living) 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(Living) 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)

Sawtooth Graph -showing seasonal population fluctuations summer winter

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

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

19 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)

Minnesota Black bear Population DNR Data: 3000 Baits with Tetracycline 165 Baits eaten by other Animals – How did they know? 935 Baits eaten by Bears – How did they know? 1750 Bears Shot by Hunters *120 of these were marked – Teeth were stained N=M X T / P

935 X 1750 Divided by 120 = 13,635 Number adjusted to 12,400 due to: Canadian migration and Bears eating Cattle Feed

Reproductive patterns 1.r-strategist: produce many offspring in a short period of time (mice, flies) take advantage of a temporarily abundant resource 2.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

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25 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: YearEstimated population (in millions) 0 A.D ,000 (1 billion) ,000 (2 billion) 19704,000 (4 billion) May ,082,300,000 U.S. 315,000,000

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

Number of years to add each billion (year) (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), All of Human History

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)

C.What is Earths’ carrying capacity? 1.Unknown 2.J curve will continue until some resource becomes limiting 3.Some countries have exceeded their carrying capacities: China, Ethiopia, Somalia, India

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Natural Increase per World More Developed Countries Less Developed Countries Less Developed Countries (less China) Year80,224,198912,05379,312,14571,498,784 Day219,7922,499217,294195,887 Minute World Population Clock Source: Population Reference Bureau, 2004 World Population Data Sheet.

34 Distribution of population growth Human Population Growth

35 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 CO 2 emissions –Poorest countries: 20% is responsible for 1.3% consumption and 3% CO 2 emissions Human Population Growth

36 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 Human Population Growth