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Population EcologyChapter 55

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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

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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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Populations

• Humans alter the environment and some species have altered their range in reponse.

Range expansion of the cattle egret

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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 PotentialThe 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 GrowthS-Curve

Exponential growth initially

Growth levels off as population approaches

carrying capacity

Popu

latio

nb = d

Lag phase

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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

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

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• North American snowshoe hare 10 year cycle• Two factors generate this cycle:

– Food plants– Predators

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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 =

13,635Number adjusted to 12,400 due to: Canadian migration and Bears eating Cattle Feed

Reproductive patterns1.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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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)0 A.D. 1301650 5001850 1,000 (1 billion)1930 2,000 (2 billion) 1970 4,000 (4 billion)1998 6000May 1 2013 7,082,300,000

U.S. 315,000,000

A.The graph of human population is a J curve. It shows exponential growth

Agriculturebegins

Plowingand irrigation

Bubonicplague

IndustrialRevolutionbegins

Ninth

Eighth

Seventh

Sixth

Fifth

Fourth

Third

Second

First Billion

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), 2003.

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. Unknown2. J curve will continue until some

resource becomes limiting3. 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)

Year 80,224,198 912,053 79,312,145 71,498,784Day 219,792 2,499 217,294 195,887Minute 153 2 151 136

World Population Clock

Source: Population Reference Bureau, 2004 World Population Data Sheet.

34Distribution of population growth

Human Population Growth

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• 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

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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