Population & Community Ecology

Chapter 35

35.1 A population is a local group of organisms of one

species

I. Defining Populations

A. A populations size is determined by the availability of food and space, weather conditions, and breeding patterns

B. When scientists study populations they must determine its boundaries, such a lake, a state or the whole country

What is a species?

• Distinct form of life

• Population of organisms which can breed and produce offspring

What about these?

Peacock + Peahen = Peachicks Horse + Donkey = Mule

Boundaries

Regional Local

II. Population Density

A. Population Density is the number of individuals of a particular species per unit of area or volume

B.Population density is useful when comparing two populations in different areas

Class Example.

III. Sampling TechniquesA. Since it is impossible to count every member

of a population scientists use sampling techniques to estimate the size of a population

1. Quadrats- scientists mark off a square boundary at several locations and take an average (plants)

2. Indirect Counting- counting nests, burrows or tracks instead of the organisms themselves (insects)

3. Mark-Recapture- scientists trap and mark individuals (birds)

B. Most sampling techniques involve making assumptions about the populations being studied

Which sampling technique?

Black bear: indirect

Bats: mark-recaptureCactus: quadrat

Population Distribution

Which distribution pattern?

Termite Mound Rattlesnake

Clumped Random

35.2 Limits to population growth

I. Exponential Growth of PopulationsA. A population’s ability to grow

partly depends on the rate at which its organisms can reproduce

B. Exponential Growth is when the population multiplies at a constant factor at constant time intervals i.e. bacteria doubling every 20 minutes

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1. Compare and contrast the two growth curves.

Both curves show a period of rapid population growth, but the fur seal population eventually levels off. The bacterial population appears to continue growing exponentially.

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2. Which curve do you think more closely resembles the growth of most populations in nature? Explain.

Limited growth curve; populations in nature are subject to limiting factors that prevent long-term exponential growth.

II. Carrying Capacity

A. A population may start to grow exponentially, but eventually one or more environmental factors will limit its growth

B. A limiting factor is a condition that can restrict a population’s growth

C. The carrying capacity is the number of organisms in a population that the environment can maintain or “carry”

III. Factors Affecting Population Growth

A. Density Dependent Factors is a factor that limits a population more as a population density increases

B. Density-Independent Factors are factors that limit population but are unrelated to population density

Population Growth

Food availability Temperature and humidity

Density- IndependentDensity-dependent

IV. Population Cycling

A. A “boom” and “bust” growth cycle is one that increases rapidly followed by a sharp decline

B. Other growth cycles are influenced by those of other populations in their environments

Population Cycling

V. Survivorship CurvesA. Type I - reflect relatively low death rates early in

life and through midlife, with a sharp increase in death rate among older-age groups (e.g., humans).

B. Type II - illustrate a fairly even mortality rate throughout the life span of the organism (e.g., birds).

C. Type III - Populations with high death rates early in life followed by a sharp decline of death rates for the survivors are represented by Type III survivorship curves (e.g., fish and many insect populations).

Survivorship Curves

35.3 Predicting the impact of human population growth

10 Largest Countries - 2009

Country Population (Millions)

1. China 1,338

2. India 1,156

3. United States 307

4. Indonesia 240

5. Brazil 190

10 Largest Countries - 2009

Country Population (Millions)

6. Pakistan 174

7. Bangladesh 156

8. Nigeria 149

9. Russia 140

10. Japan 127

10 Largest Countries - 2050

Country Population (Millions)

1. India 1,614

2. China 1,417

3. United States 404

4. Pakistan 335

5. Nigeria 289

10 Largest Countries - 2050

Country Population (Millions)

6. Indonesia 288

7. Bangladesh 222

8. Brazil 219

9. Ethiopia 174

10. Rep. of Congo 148

History of Human Population

History of Human Population

Human Pop Graph 6.7 Billion in 2009

9.3 Billion in 2050

I. History of Global Population GrowthA. For most of human history, the human

population has grown very slowly or not at allB. Human population growth depends on birth

rates and death ratesC. The introduction of farming has provided a

stable food supply so birth rates have gone upD. Advances in modern medicine, nutrition and

sanitation have caused death rates to go downE. These factors have caused the human

population to increase dramatically

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1. Which age group forms the largest bulge in the age-structure graph of the United States? Of Kenya?

40–44; under 5

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2. Which country is likely to undergo the greatest increase in population in the next 20 years? Explain.

Kenya; the majority of the population is under 25 years old, which is the portion likely to have children in the next 20 years.

II. Predicting Future Population Growth

A. The Age Structure of a population is the proportion of people in different age groups

B. Prediction of future growth varies because of the difficulty predicting future birth and death rates of various countries

C. The question remains whether or not Earth will have the capacity for the human population

35.4 Species interact in biological communities

I. Competition Between SpeciesA. Members of a population may compete for the

same limited resourceB. Within a community, interspecific competition

takes place when two or more species rely on the same limited resource

C. If two species are so similar in their requirements that the same resource limits both species’ growth it is called competitive exclusion

D. A niche includes an organisms living place, its food source, the time of day it is most active and many other factors that are specific to that organism’s way of life

Competitive Exclusion

                                   

                       

II. PredationA. Predation is when one organism eats another B. Eating and avoiding being eaten are important to

survival and predators and prey have developed many adaptations1. Predator adaptations include: being fast and

agile, coloring that camouflages, hunting in groups, acute sense to find prey and having claws, teeth, fangs and stingers to help catch prey

2. Prey adaptations include: retreating or fleeing from predators, camouflage, defensive coloring, mimicry, secreting poisonous chemicals, having spines and thorns

Predator-Prey

Relations

III. Symbiotic relationshipsA. A symbiotic relationship is when two species live

in or on one another

B. There are three main types of symbiotic relationships

1. Parasitism- A parasite gets it’s food at the expense of another organism, i.e. mosquitos and humans

2. Mutualsim- Both organism benefit from the relationship, i.e. E.Coli and humans

3. Commensalism- One organism benefits and the other is neither hurt nor helped, i.e. sharks and remoras

Symbiosis

Parasitism Win

+

Lose

-

Mutualism Win

+

Win

+

Commensalism Win

+

Tie

0

Symbiosis - Which is it?

Liver Fluke Mongoose & Cobra

Predator-PreyParasitism

Symbiosis - Which is it?

Clownfish & Anemone

Air Plant

CommensalismMutualism

35.5 Disturbances in communitiesI. Disturbances to Communities

A. Natural Disturbances are events such as fires, volcanic eruptions, floods, storms, and droughts all destroy resources such as shelter and water

B. Disturbances can be either positive or negative

C. Humans also have an impact on communities which can be either positive or negative

Surviving Environmental Change

II. Ecological SuccessionA. The series of changes in the species in a

community, often following a disturbance is known as ecological succession

B. There are two types of succession:1. Primary succession which is when new

community arises from a previously lifeless area i.e. plants growing on a volcanic island

2. Secondary succession is when a new community arises from a previous community i.e. a forested are which has been cleared and abandoned

Primary Succession

Secondary Succession

III. Human activities and species diversity

A. 60% of the Earth’s land is used by humans, mainly for cropland or rangeland

B. Humans usually have a negative effect on species in two ways1. Clearing the Land- Humans clear vast amounts

of land to make way for farming and building2. Introduced Species are species that are moved

from one location to another either accidentally or on purpose. These new species may take over an area and prey on native species or drive them from their niches

Invasive species in Ohio

Emerald ash borer

Canada thistle

Zebra mussel

Dutch Elm disease