6. Living things and the World1. Ecology and the Dynamics of

Populations• Ecology is the study of the interactions of living things

with each other and with their environment.• Based on field observation of living plants and

animals and/or

• mathematical models that simulate the workings of the natural world

Ecology ≠ environmentalism.• Environmentalism refers to the movement

advocating conservation of natural resources

• Ecology and environmental science Environmental science applies ecological

principles to practical human concerns

Conservation biology• New discipline that studies all aspects of

biodiversity• Goal of conserving natural resources

including wildlife for benefit of future generations

The human population• Human population has a clumped

distribution.

• 56% of the world’s people live in Asia.

• Most Asian populations live in China and India.

• Mongolia has a population density of 0.25 persons per square kilometer.

• Bangladesh has a density of over 1,000 persons per square kilometer.

Growth of human population was originally slow. Industrial revolution increased food and jobs. Population then began to increase steeply.

IndustrialRevolution

Modern Scienceand Medicine

Black Plague

Implications?

Growth rate of population

Current global birth rate is 20 per 1,000 per year.

Current global death rate is 8 per 1,000 per year.

Current annual growth rate =(Birth rate) – (death rate)

Per 1,000 per year, this =(20-8)/1,000 = (12)/1,000 = 1.2%

Future population growth Doubling time for human population is 35 years.

• Already have areas across the globe where people have inadequate access to fresh water, food, and shelter.

• In 35 years, we need to double the amount of food, water, energy and other resources to maintain the present standard of living.

Rapid growth usually begins to decline when resources become scarce.

• Population levels off at carrying capacity of the environment.

• Earth’s carrying capacity for humans has not been determined.

Not all countries have the same growth rate.

Global population growth rates

More-developed countries

• North America and Europe

• Population growth is modest.

• People enjoy a fairly good standard of living.

Less-developed countries

•Latin America, Asia, and Africa•Population growth dramatic•Majority of people live in poverty.

• More Developed Countries (MDCs) Did not always have a low growth rate

• Between 1850 and 1950 their populations doubled Largely because of decline in death rate

• Followed by decline in birth rate• Only modest growth since 1950

Overall growth rate is 0.1% but some countries are not growing at all or decreasing in size.

• Higher growth rate of US (0.6%) due to immigration and large number of women of reproductive age

• Less Developed Countries (LDCs) Death rates began to decline rapidly after WWII

(introduction of modern medicine).

Birthrate remained high.

Collective growth rate peaked at 2.5% between 1960-1965.

Rate has declined to 1.6%.

Growth rate in 46 countries have not declined. Population is expected to jump to 8 billion by

2050.• The majority of growth will be in Asia.• Africa has a high death rate due to AIDS.

Age Structure Diagrams (1998) More-developed countries (MDCs)

•Many More Developed Countries have a stable age structure –number in each category about the same

•If replacement reproduction occurs (each couple has 2 children), then population remains the same……

Male Female Postreproductive

Reproductive

Dependent

• Most LDCs have a pyramid shaped age structure.• LDC population will continue to expand, even after

replacement reproduction attained, as more young women reach reproductive age.

Male Female Postreproductive

Reproductive

Dependent

Population growth and environmental impact Increasing LDC populations might seem to be

the main cause of future environmental degradation.

MDCs, however, consume a much larger percentage of the Earth’s resources.

• Consumption leads to degradation.

Environmental impact (EI) = population size x resource consumption per capita

= pollution per unit of resources used

2 possible causes of environmental impact

1. Population size More obvious in less well-developed countries

2. Resource consumption More obvious in more well-developed countries

• An average American family is the equivalent of 30 people in India in terms of per capita resource consumption and water requirements.

• Watch the following slides...

Environmental Impactof LDCs and MDCs

Age Structure…one more wrinkle

$$$

Male Female

Male Female

Male Female

Postreproductive

Reproductive

Dependent

Postreproductive

Reproductive

Dependent

Postreproductive

Reproductive

Dependent

IncreasingPopulation

StablePopulation

DecreasingPopulation

Characteristics of populations• Various characteristics of all populations

change over time.

• Periodically subject to environmental instability

• Individuals then under the pressure of natural selection

• Better adapted individuals leave behind more offspring than less adapted individuals.

Survivorship CurvesThe time in an organism’s life span when most death occurs

Thinking about Human Populations • Actuaries (who analyze risk) use survivorship curves

to calculate probable death rates in various age groups in humans

• (to help insurance companies set premiums and make other business decisions).

• Pigs – high Produce many

offspring that reach maturity quickly

• Rhinos – low Only 1 or 2

offspring per infrequent reproductive event

Survivorship works in tandem with reproduction rate/method

“Biotic potential”: who recovers more quickly, or even survives, a catastrophe?

Population Growth Curves

•When resources are unlimited, populations exhibit exponential growth.•When resources are limited, populations exhibit logistic growth, which levels off when the carrying capacity of the environment is reached.

Carrying capacity of the environment

What factors might cause fluctuation?

Num

ber o

f Org

anis

ms

stable equilibrium phase

carrying capacity

decelerationphase

exponentialgrowthphase

Lag phase Time

Knowledge of Growth Patterns:Diverse strategies apply

To use a fish population as a food source, we must maintain it in the exponential phase.

To reduce the number of pests, we must reducethe environmental carrying capacity rather than reduce population size

• the second option encourages exponential growth.

Overfishing may push the population into lag phase that takes years to recover.

Factors that regulate population growth Both biotic (living) and abiotic (nonliving)

components regulate population size.

Density-independent factors• Abiotic factors such as weather or natural disasters• Can cause sudden and catastrophic reductions in

population size• Intensity of effect does not increase with increased

population size.

Consider 2 populations of rabbits in the path of a flash flood

A) low density population has 3 out of 5 mice drown = 60% death rate

Density-independent factors

B) high density population has 12 out of 20 mice drown = 60% death rate.

What might this do to the gene pool of the population????

Recall Genetic Drift

Density-dependent factors• Biotic factors – competition, predation,

parasitism• Percentage of population affected does

increase as population density increases.• Intensity of effect increases as density

increases.

• Competition Members of a species compete to utilize resources

– light, food, or space- that are in limited supply and necessary for survival. Not all members can have access to a necessary

degree.

Competition•Woodpeckers compete for nesting sites.

•Each pair requires a tree hole to raise offspring.

•More holes than pairs, every pair gets a hole.

•Fewer holes than pairs, some pairs do not get a hole and do not reproduce.

Density-dependent effect

What might this do to the gene pool of the population????

Predation As prey increase in

number, predators also increase

The slowest, or least camouflaged individuals are likely to be preyed upon.

Density-dependent effect

What might this do to the gene pool of the population????

• Shows pattern of 10-year cycles in population densities

• Snowshoe hare population reaches peak a year or more before lynx population.

Hare and Lynx….

Predator-prey population cycles

Life/Reproduction StrategySuccess & Extinction

1. Opportunistic life history pattern Tends to exhibit exponential growth

Members of population are small in size, mature early, have short life span, and provide limited parental care for a large number of offspring.

Tend to be regulated by density-independent effects

Population has high dispersal capacity

Examples – insects and weeds

2. Equilibrium life history pattern Exhibit logistic population growth

Size of population remains close to or at carrying capacity.

Members of the population are large, slow to mature, and have fairly long life spans.

Growth regulated by density-dependent effects

Examples – birds and mammals

• Extinction Total disappearance of a species or higher

group

Equilibrium species more apt to go extinct

• Size of geographic range, degree of habitat tolerance, and size of local population can help determine danger of extinction.

Levels of organization

Population

Community

Ecosystem

Organism

Biosphere

An individual

All the members of a species in a single location

All of the populations in a single location

All of the populations in a single location and the environment of that location

All of the ecosystems

Our Biosphere is the planet Earth

Ecology began as a part of natural history –observing and describing organisms in their environment Now an experimental science Central goal to develop models that explain and

predict distribution and abundance of populations based on their interactions within an ecosystem It can be used to predict which species will

survive a change, or repopulate after a catastrophe

• Ecologists might formulate and test hypotheses about the role fire plays in maintaining a lodgepole pine forest.

• Could compare characteristics of a community before and after a prescribed burn…

Succession of species

Succession in an oak and hickory forest after a forest fire.

Mt. St. Helens

Look who’s back first…

Succession………

the 1883 eruption of the Indonesian volcano Krakatoa blasted enough volcanic ash into the atmosphere to lower global temperatures by 2.2oF for an entire year

in 1815, the eruption of Mount Tambora in Indonesia blocked enough sunlight around the globe to cause what came to be known as "the year without summer…That following year, residents in the United States experienced summer snows and temperatures between 5 – 10oF less than average.

The difference in the human population from 1800 until now, and beyond, is critically dependent upon our technology.

IndustrialRevolution

Modern Scienceand Medicine

Black Plague

If another asteroid hits, and our technology fails, what species will repopulate?