Understanding Populations

Chapter 8 p.196- 217

Key Terms

• Populations• Density• Dispersion• Growth rate• Reproductive potential• Exponential growth• Carrying capacity

• Niche• Competition• Predation• Parasitism• Mutualism• Commensalism• Symbiosis

Objectives

• Describe the 3 main properties of a population• Describe exponential population growth• Describe how the reproductive behavior of

individuals can affect the growth rate of their populations

• Explain how populations sizes in nature are regulated

What is a Population?

• All the members of a species living in the same place at the same time.

Properties 1. size- 2. density- the number of individuals per unit

area or volume 3. Dispersion- is the relative distribution or

arrangement of its individuals within a given amount of space

Dispersion Patterns

• Within a population’s geographic range, local densities may vary greatly.

• The dispersion pattern of a population refers to the way individuals are spaced within their area.

• These patterns are important characteristics for an ecologist to study, since they provide insights into the environmental effects and social interactions in the population. 1. Clumped2. Uniform3. Random

Dispersion Patterns

Clumped pattern

– Most common in nature– Individuals are aggregated in patches– Often results from an unequal distribution of resources in

the environment. • For example, plants or fungi may be clumped in areas where

soil conditions and other factors favor germination and growth.

– Clumping of animals is often associated with uneven food distribution or with mating or other social behavior.

• For example, fish are often clumped in schools, which may reduce predation risks and increase feeding efficiency. Mosquitoes often swarm in great numbers, increasing their chances for mating.

Uniform, or even, pattern

– Pattern of dispersion often results from interactions between the individuals of a population.

• For example, some plants secrete chemicals that inhibit the germination and growth of nearby plants that could compete for resources.

– Animals may exhibit uniform dispersion as a result of territorial behavior.

• For example, penguins and humans

Random dispersion

– Individuals in a population are spaced in a patternless, unpredictable way.

• For example, clams living in a coastal mudflat might be randomly dispersed at times of the year when they are not breeding and when resources are plentiful and do not affect their distribution.

– Varying habitat conditions and social interactions make random dispersion rare.

How does a Population Grow?

• Birth rates and death rates change in rate is the growth rate

• Can be +, -, or even 0Equation:Change in the population size =Birth rates – Death Rates(You can also look at immigration and

emigration)

How Fast Can a Population Grow?

• A female sea turtle can lay 2,000 eggs many will dieReproductive potential- limited buy the number of

offspring an individual can have – 750 years for a pair of elephants to produce 19 million

decedents– One bacteria can produce 19 million decedents in a few

days• Can change or increase based on when reproduce,

how many offspring, how often they reproduce • Small organisms short life span high reproduction rate

and vise versa

Exponential Growth

• They grow faster and faster– Dog has 6 puppies and they each have 6 puppies

and so on• This can occur if there is plenty of food and

space and there is no competition or predators

Logistic Growth Model (Carrying Capacity)

– A description of idealized population growth that is slowed by limiting factors as the population size increases. (can be both abiotic and biotic factors)

• Limiting factors are environmental factors that restrict population growth.

• carrying capacity is the maximum population size that a particular environment can support or “carry”

– S-shape curve or J- shaped • 1. Exponential Growth Phase-When the population first starts growing,

population growth is close to exponential growth• 2. Transitional Phase- The population growth starts to slow• 3. Plateau Phase- Carrying capacity is reached and the population is as big

as it can theoretically get in its environment

What Limits Population Growth?

• Environments are never constant and populations cannot grow forever and rarely grow at their reproductive potential

• Environments can change and resources can be used up populations can change over time

1. Carrying Capacity maximum number of a species that an environment can sustain

• Difficult to determine, often by population averages or after large population crash

carrying capacity• In order to determine what a sustainable population level might be, we

need to understand the ecological concept of carrying capacity. Carrying capacity is the population level of an organism that can be sustained given the quantity of life supporting infrastructure available to it. If the numbers of an organism are below the carrying capacity of its environment, its birth rate will increase. If the population exceeds the carrying capacity, the death rate will increase until the population numbers are stable. Carrying capacity can be increased by the discovery and exploitation of new resources (such as metals, oil or fertile uninhabited land) and it can be decreased by resource exhaustion and waste buildup, for example declining soil fertility and water pollution.

Determining Population GrowthLogistic Growth Curves

overshoot

• In ecology, overshoot is said to have occurred when a population's consumption exceeds the carrying capacity of its environment, as illustrated in this graphic:

World Population• An increase in the carrying capacity of an environment can generally be

inferred from a rise in the population inhabiting it. The stronger the rise, the more certain we can be that the carrying capacity has expanded. In our case a graph of world population makes it obvious that something (OIL) has massively increased the world's carrying capacity in the last 150 years. During the first 1800 years of the Common Era, like the tens of thousands of years before, the population rose very gradually as humanity spread across the globe. Around 1800 this began to change, and by 1900 the human population was rising dramatically: What happens when oil runs out?

What Limits Population Growth?

2. Resource Limits or limiting resource can determine the carrying capacity

3. Competition within a population- competition for the same resources, shelter, food or breeding sites, predator/ prey

Territory- area defended by one or more individuals against other s

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Limiting factors

Factors that influence an organism into two types1. Living components- biotic factors2. Nonliving factors- abiotic factors (changing)

a) Temperatureb) Humidityc) pHd) Salinitye) Oxygen concentrationsf) Amount of sunlight

Web cd 34 b

2 types of Population Regulations

1. Density Dependent – death is a result of over population

• Competition among members of a growing population for limited resources, like food or territory.

• Health of organisms• Predation• Physiological factors (reproduction, growth, hormone changes)

2. Density Independent- death is a result regardless of the population size

– Weather conditions– Acidity– Salinity– Fires– Catastrophies

8.2 How Species Interact with Each Other

• Explain the difference between niche and habitat

• Give examples of parts of a niche• Describe the five major types of interactions

between species• Explain the difference between parasitism and

predation• Explain how symbiotic relationships my evolve

An Organism’s Niche

• Unique role of a species within an ecosystem• Physical home, abiotic and biotic factors, but it

is not the same as a habitat which is the location

• Job or role in ecosystem

Keystone Species

Sometimes changes in the population of a single species, often called a keystone species, can cause dramatic changes in the structure of a community. – In the cold waters off the Pacific coast of North America, for example,

sea otters devour large quantities of sea urchins.

– Urchins are herbivores whose favorite food is kelp, giant algae that grow in undersea “forests.”

– A century ago, sea otters were nearly eliminated by hunting. Unexpectedly, the kelp forest nearly vanished.

– Without otters as predators, the sea urchin population skyrocketed, and armies of urchins devoured kelp down to bare rock.

– Without kelp to provide habitat, many other animals, including seabirds, disappeared.

– Otters were a keystone species in this community.Ecology 2010

Species interactions

• Competition- -/-– Indirect- use same resources but never actually occupy

same time (night/day) (intraspecific and interspecific) – Adaptations (resource partition/ reduced niche)

• Predation- +/-• Parasitism- +/- (require host to survive)• Mutualism- +/+• Commensalism- +/ 0• Symbiosis and coevolutoin

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Types of Competition1. Interspecific competition- type of interaction in

which two or more species use the same limited resources (plants and sunlight)

2. Intraspecific competition- same species Web cd 37 A3. Competitive exclusion- one species gets eliminated

from the community due to resources4. Reduce niche size- interactions with other species,

-fundamental- potentially use, -realized niche- what is actually used

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The Competitive Exclusion Principle

– The competitive exclusion principle states that no two species can occupy exactly the same niche in exactly the same habitat at exactly the same time.

– If two species attempt to occupy the same niche, one species will be better at competing for limited resources and will eventually exclude the other species.

– As a result of competitive exclusion, natural communities rarely have niches that overlap significantly.

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The Competitive Exclusion Principle

– In the experiment shown in the graph, two species of paramecia (P. aurelia and P. caudatum) were first grown in separate cultures (dashed lines) . In separate cultures, but under the same conditions, both populations grew. When organism were put in the same culture one species dies off.

– However, when both species were grown together in the same culture (solid line), one species outcompeted the other, and the less competitive species did not survive.

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Ecology 2010

Types of Competition4. Character displacement- evolution of

differences in a characteristic due to competition, way to reduce niche overlap, finches

5. Resource partitioning- when similar species coexist each species may avoid competition with others by using a specific part of an available resource (warbler eating insects at diff parts of tree)

Dividing Resources

– Instead of competing for similar resources, species usually divide them.

– For example, the three species of North American warblers shown all live in the same trees and feed on insects.

– But one species feeds on high branches; another feeds on low branches, and another feeds in the middle.

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Parasitism

• A parasite lives on or in its host and obtains its nourishment from the host.

– For example: A tapeworm is an internal parasite that lives inside the intestines of a larger animal and absorbs nutrients from its hosts.

– Another example: Ticks, which suck blood from animals, and aphids, which tap into the sap of plants, are examples of external parasites.

• Natural selection favors the parasites that are best able to find and feed on hosts, and also favors the evolution of host defenses.

• http://oldnewsbaby.com/site/click/8b0c2347f6ec462a9f82592cb0a664c7

• http://user.it.uu.se/~svens/larverna/normal.html

• http://www.neatorama.com/2006/08/21/six-horrifying-parasites/

Tapeworm in Small Intestine

Tick on a dog

Commensalism• One partner benefits without significantly affecting the

other. • Few cases of absolute commensalism have been

documented, because it is unlikely that one partner will be completely unaffected.

• For example: algae that grow on the shells of sea turtles, barnacles that attach to whales, and birds that feed on insects flushed out of the grass by grazing cattle.

Algae on Sea TurtleBarnacles on Whale

Mutualism

• Benefits both partners in the relationship.• For example: the association of legume plants and

nitrogen-fixing bacteria.– Bacteria turn nitrogen in the air to nitrates that the plants can

use

• Another example: Acacia trees and the predaceous ants they attract.

– Tree provides room and board for ants – Ants benefit the tree by attacking virtually anything that touches

it.

Acacia Trees and Ants

Examples

1. Tapeworms live in the intestines of mammals, where they absorb large amounts of their hosts’ food.

– Fleas, ticks, lice, and the leech shown, live on the bodies of mammals and feed on their blood and skin.

2. The sea anemone’s sting has two functions: to capture prey and to protect the anemone from predators. Even so, certain fish manage to snack on anemone tentacles.

The clownfish, however, is immune to anemone stings. When threatened by a predator, clownfish seek shelter by snuggling deep into an anemone’s tentacles.

3. Barnacles often attach themselves to a whale’s skin. They perform no known service to the whale, nor do they harm it. Yet the barnacles benefit from the constant movement of water—that is full of food particles—past the swimming whale.

Ecology 2010

Chapter 9: The Human Population

P218- 233

Key Terms

• Demography• Age structure• Survivorship• Fertility rate• Migration• Life expectancy

• Demographic transition• Infrastructure• Arable land• Urbanization• Least developed

countries

objectives• Describe how the size and growth rate of the human

population has changed in the last 200 years• Define four properties that scientists use to predict

population size• Make predictions about population trends based on

age structure• Describe the four stages of the demographic

transition• Explain why different countries may be at different

stages of the demographic transition

9.1 Studying Human Populations

• How have the human populations changed in the US in the past 50 years ?

• What problems can occur if human population growth too rapidly?

9.1 Studying Human Populations

• Populations grew faster in the 20th century that it has before leads to environmental problems

• Demography- is the study of populations, but most often refers to the study of human populations

• Study historical size and makeup to make predications

• Economics and social structure that can impact populations (developed vs. developing)

Human Populations Over Time

• 1800s populations begin to grow exponential due to increase in food, medical, hygiene Earth is reaching it carrying capacity

Forecasting Population size

• What resources will your community need in 20 years? (schools, retirement communities, roads, utilities)

• Constant changes due to human behavior1. Age structure2. Survivorship3. Fertility rates4. Migration/emigration

Age Structure Diagrams

Survivorship curves fit three types.

Is the percentage of members of a group that are likely to survive to any given age1. Type I curve shows a low death rate in early and middle

life but the death rate increases steeply in old age. Produce few offspring, take care of their young, many survive into maturity (Japan/ Germany)

2. Type II curve shows a death rate is more constant throughout the lifetime of the species.

3. Type III high death rates for the very young, mature individuals survive longer, usually involves very large # of offspring with little or no parent care

http://www.quia.com/rr/486328.html?AP_rand=598176044

Questions:1. Which curve would fit an organism that cares for

its young and reproduces relatively late in life? Type I

2. Which curve would be typical of an organism that experiences high predation as small individuals but when they are adults are more able to avoid most predators?. Type III

3. Which curve might best fit rodents that die in numbers at all ages? Type II

Declining Death Rates

• Recent years death rates have decreased more rapidly than birth rates

• Adequate food, clean water, medical and sanitation

• Life expectancy- average number of years a person is likely to live (67 years)

The Demographic Transition

• Describes how these changes can occur, based on observations of history of many developed countries

• Developed countries stopped growing• Industrial development causes economic and

social progress that affects pop growth

Stages of the Transition• 1st- preindustrial condition- BR and DR are both

at high levels and pop size stable• 2nd- Transitional- pop explosion; death rates

decline and birth rates remain high pop grows fast

• 3rd- Industrial- pop growth slow; birth rates decrease; BR close to DR pop stabilizes; pop still large

• 4th- Postindustrial- BR drops below replacement level; pop decrease

Stages of Demographic Transition

Women and Fertility

• Education and economic independence for women

• Cost of child care; waiting past fertility • Developed countries 1.6 children• Developing countries 3.1 children

9.2 Changing Population Trends

• Describe three problems caused by rapid human population growth

• Compare population growth problems in more-developed countries and less developed countries

• Analyze strategies countries may use to reduce their population growth

• Describe worldwide populations into the next century

Changing Population Trends

• Populations that have high rates of growth create environmental problems

• Rapidly growing population uses resources at an increase rate and can overwhelm the infrastructure of a community.

• Infrastructure is the basic facilities and services that support a community, such as public water supplies, sewer lines, power plants, roads subways, schools and hospitals

Problems of Rapid Growth

• Limited resources (vegetation, water and land)• Standards of living can decline

– Shortage of fuelwood– Unsafe water– Arable land- used to grow crops– Urbanization- city living rather than rural

(suburban sprawl)

Demographically Diverse World

• More or less developed• Development is complex and politically sensitive• Modern industries but income low• Stable and educated populations but little

industrialization• Focus on least developed countries- few signs of

development • More developed slow population growth• Less developed faster population growth

Managing Development and Population Growth

• China, Thailand, India campaigns to reduce the fertility rates of citizens (public advertising, family planning program, economic incentives, legal punishments)

• 1994- UN held International Conference on Population and Development (ICPD)- favor stabilizing population growth through investments in development, improvements in women’s status

Growth is Slowing

• Human pop is 6 billion ww• Peaked at 87 million people per year between

1985 and 1990• 1990-1995 pop grew 81 million• Fertility rates have declined since 1970s• 2050 predict low fertility rates and world

population of 9 billion

US Fertility Rate

Over