Chapter 21 Lecture Conceptual Integrated Science Second Edition © 2013 Pearson Education, Inc. Ecology

Chapter 21 Lecture

ConceptualIntegrated Science

Second Edition

© 2013 Pearson Education, Inc.

Ecology


This lecture will help you understand:

• Organisms and Their Environments• Population Ecology• Human Population Growth• Species Interactions• Kinds of Ecosystems• Materials Cycling in Ecosystems• Energy Flow in Ecosystems• Energy Leaks When Organisms Eat• Change in an Ecosystem• Math Connection: Exponential and Logistic Population Growth• Science and Society: Biodiversity, Nature's Insurance Policy• Science and Society: Invasive Species• Science and Society: Wangari Maathai and Ecologically Sustainable

Development


Organisms and Their Environments

• Ecology is the study of how organisms interact with their environments.

• An organism's environment includes abiotic (nonliving) and biotic (living) components.

• Ecology can be studied at the level of the individual, population, community, or ecosystem.


Organisms and Their Environments

• A population is a group of individuals of a single species that lives in a specific area.

• A community consists of all the organisms that live in a specific area.

• An ecosystem consists of all the organisms that live in a specific area and all the abiotic features of their environment.


Organisms and Their EnvironmentsCHECK YOUR NEIGHBOR

Prairie dogs living in Nebraska represent

A. a species.

B. a population.

C. C. a community.

Explain your answer to your neighbor.


Organisms and Their EnvironmentsCHECK YOUR ANSWER

Prairie dogs living in Nebraska represent

A. a species.

B. a population.

C. C. a community.


Population Ecology

• Population ecologists are interested in how a population's size changes over time.

• They may count the total number of individuals in a population or measure population density.

• Changes in population size over time depend on the contributions of four variables:– Birth rate– Death rate– Rate of immigration into the population– Rate of emigration out of the population


Population Ecology

• Exponential growth occurs when a population grows at a fixed rate per amount of time.

• Exponential growth occurs when a population has unlimited resources.

• Exponential growth cannot continue forever.


Population Ecology

• Logistic growth occurs when population growth slows as the population size approaches the habitat's carrying capacity.

• The carrying capacity is the maximum number of individuals or maximum population density the habitat can support.

• Many factors can cause population growth to slow as the population size increases.


Population Ecology

• An organism's life history strategy describes its schedule of survival and reproduction.

• Survivorship curves


Population Ecology

Typical characteristics of Type I and Type III

populations


Human Population Growth

• More than 7 billion people live on Earth today.• World population is expected to exceed 10

billion by 2100.• Growth is expected to slow in the second half of

this century.



Age structure diagrams reveal how populations are

growing.



• Many human populations have undergone a demographic transition, a shift from high birth and death rates to low birth and death rates.

• Usually, the death rate decreases first due to medical and public health advances. Later, the birth rate declines.

• During the period between the fall in the death rate and the fall in the birth rate, the combination of low death rate and high birth rate causes the population to grow very rapidly.



• An ecological footprint is a measure of how much land and water area a human population needs in order to produce the resources it consumes.

• The global human population has been in ecological overshoot for more than 30 years, consuming more resources each year than Earth can provide.

• We would need 1.5 Earths to sustain our current rate of consumption.

• If everyone in the world consumed as much as the average American, we would need 5.3 Earths!


Species Interactions

• Food chains and food webs describe which species eat which other species.

• The feeding levels in a food chain include producers, consumers, and decomposers.



The Antarctic aquatic food web



• Interspecific competition occurs when two species use the same resource and it is found in limited supply.

• Many adaptations evolve as a result of interspecific competition.

• A species' niche within a community is the total set of biotic and abiotic resources it uses.

• No two species in a community can have exactly the same niche.



• Symbiosis is a situation in which individuals of two species live in close association with one another.

• Parasitism benefits one member of the interaction and harms the other.

• Commensalism benefits one species while having no effect on the other.

• Mutualism benefits both members of the interaction.


Kinds of Ecosystems

Terrestrial ecosystems—eight major biomes


Kinds of Ecosystems

Tropical forests

Coniferous forests

Temperate forests

Tundra


Kinds of Ecosystems

Savannas

Chaparral

Temperate grasslands

Deserts


Kinds of EcosystemsCHECK YOUR NEIGHBOR

True or false? All of Earth's deserts are located in

a band around 30 degrees north latitude and 30

degrees south latitude.

Explain your answer to your neighbor.


Kinds of EcosystemsCHECK YOUR ANSWER

False. Deserts are defined by the low level of

precipitation they receive, and they are found in

many different parts of the world. For example,

Antarctica is a desert. Like all deserts, Antarctica

receives very little precipitation. When it falls, it is

in the form of snow.


Kinds of Ecosystems

• Aquatic ecosystems include freshwater and saltwater habitats as well as estuaries where fresh water and saltwater meet.

• Freshwater habitats:– Lakes and ponds– Rivers and streams


Kinds of Ecosystems

• All lakes and ponds can be divided into three zones:– Littoral zone—close to the water surface and to shore – Limnetic zone—close to the water surface but far from

shore – Profundal zone—deep-water habitats in ponds and

lakes


Kinds of Ecosystems

• Estuaries are habitats where freshwater rivers join oceans.

• Estuarine plants, such as certain seaweeds, marsh grasses, and mangroves, have adaptations that allow them to deal with changing salinity conditions.

• Estuaries are essential habitat for many species.


Kinds of Ecosystems

• Ocean habitats are divided based on their depth in the water column and their proximity to shore.

• Pelagic zone—in the water column– Photic zone—close to the water surface, where photosynthesis

is possible– Aphotic zone—deeper and receives little sunlight, more limited in

food availability and biodiversity• Benthic zone—on the ocean bottom


Kinds of Ecosystems

Intertidal zone– Closest to shore– Periodically under water and exposed to air as the

tide moves in and out– Many species specialized for life

Neritic zone– Under water marine habitats near the coasts, such as

coral reefs– High levels of nutrients that have washed into the

water from land

Oceanic zone– Even farther from shore


Materials Cycling in Ecosystems

• Many substances move around Earth in biogeochemical cycles, going back and forth between the tissues of living organisms and the abiotic world.

• Three of these cycles involve water, carbon, and nitrogen.



• Water cycle– Water evaporates from the oceans

into the atmosphere.– Water is moved around the

atmosphere by winds.– Water precipitates as rain or snow

over ocean or land.– Water moves into the biotic world

when it is absorbed or swallowed by organisms.

– Some of this water passes up the food chain.

– Water is returned to the abiotic environment through animal respiration, perspiration, excretion, elimination, and plant transpiration.



• Carbon cycle– Most of the inorganic carbon on Earth

exists as carbon dioxide and is found in the atmosphere or dissolved in ocean waters.

– Plants and other producers convert carbon dioxide to glucose during photosynthesis.

– Carbon is returned to the environment by living organisms as carbon dioxide, a product of cellular respiration.

– Burning fossil fuels also releases carbon dioxide. Because atmospheric carbon dioxide traps heat on the planet, this has resulted in global warming.



• Nitrogen cycle– Nitrogen is found primarily as

nitrogen gas in Earth's atmosphere. – In order for living organisms to make

use of nitrogen, it has to be converted into usable form. Living organisms rely on bacteria to accomplish this transformation. Nitrogen is converted to ammonium by nitrogen-fixing bacteria in soil, and then to nitrates by nitrifying bacteria.

– Nitrogen returns to the abiotic environment when it is converted to nitrogen gas by denitrifying bacteria.


Energy Flow in Ecosystems

• All organisms need energy in order to survive, grow, and reproduce.

• In most ecosystems, energy comes ultimately from the Sun.

• Photosynthesizing organisms convert sunlight energy into energy stored in organic molecules.

• Biomass is the amount of organic matter in an ecosystem.

• The rate at which an ecosystem's producers build biomass is the ecosystem's primary productivity.


Energy Flow in Ecosystems

• On average, only about 10% of the energy at one level of the food chain is available to the next level of the food chain.

• The other 90% includes:– Uneaten organisms– Heat lost to the environment– Energy lost in feces– Energy used for maintenance


Energy Leaks When Organisms Eat

• Every chemical reaction involves some energy loss to the environment as heat.

• This includes all the chemical reactions that occur in living things.


Change in an Ecosystem

• Ecological succession describes how the community of species living in an ecosystem changes over time.

• There are two types of ecological succession: primary succession and secondary succession.



• Primary succession– Primary succession occurs when bare land

devoid of soil is colonized by successive waves of living organisms.

• Examples: New land is formed by volcanic activity; a glacier's retreat reveals bare rock.

– Pioneer species survive with few nutrients and little existing organic matter and cope with direct sunlight and the variable temperatures that result from lack of cover.

– Pioneer species may be succeeded by grasses, shrubs, and finally trees.



• Primary succession (continued)– Ecological succession ends with a climax community. – During the process of succession, the total biomass of

the ecosystem typically increases, as does the number of species.



• Secondary succession– Secondary succession occurs when a disturbance

destroys existing life in a habitat but leaves the soil intact.

• Examples: fires, abandonment of old farmland

– Because soil is already present, secondary succession proceeds more quickly than primary succession.



Intermediate disturbance hypothesis:• Regular disturbances, if not too extreme,

actually contribute to biodiversity because different species make use of different habitats, and periodic disturbances guarantee that there will always be habitat at varying stages of recovery.


Math Connection: Exponential and Logistic Population Growth

N = population size r = rate of increase, how many offspring (on average) an individual

contributes to the population during a specific amount of timeK = carrying capacity


Science and Society: Biodiversity, Nature's Insurance Policy• Biodiversity describes the number and variety of

species found in a community.• Studies show that diverse communities are more

stable and more productive. • Greater stability may result from more species

sharing a given role.• Greater productivity may result from more

species using up a habitat's resources more completely.

• It is harder for new species to successfully invade a diverse habitat.


Science and Society: Invasive Species

• Invasive species are species that have moved from their native habitat to a new habitat, where they do a lot of ecological damage.

• Invasive species are wholly or partly responsible for over one-third of the species listed as endangered under the Endangered Species Act.

• Many invasive species also have an economic impact.


Science and Society: Wangari Maathai and Ecologically Sustainable Development• Maathai founded the Green

Belt Movement in Kenya, which organizes volunteers to plant indigenous trees.

• Tree planting is an entry point for other activities, including conservation, community consciousness, equity, livelihood security, and accountability.

• Maathai received the 2004 Nobel Peace Prize.

Documents

Chapter 21 Lecture Conceptual Integrated Science Second Edition © 2013 Pearson Education, Inc. Ecology