Chapter 23*

Ecology and the Environment

The Organization of Ecological Systems

• The smallest living unit is the individual organism.

• Populations are groups of organisms of the same species.

• Communities are interacting groups of populations of different species.

• An ecosystem consists of all the interacting organisms in an area and their interaction with their abiotic surroundings.

Environment

Ecology – study of relationships between organisms and environment.

Factors:Biotic – livingAbiotic – nonliving

Ecological systems

Ecosystems

• Those organisms that trap sunlight for photosynthesis are called producers, since they produce organic material from inorganic material. They include green plants, algae, and cyanobacteria. They convert sunlight energy into the energy contained within the chemical bonds organic compounds.

• The organisms that obtain energy in the form of organic matter are called consumers. All animals are consumers. They either eat plants directly or eat other sources of organic matter derived from plants.

• Each time the energy enters a different organism it is said to enter a different trophic level. It is a step or stage in the flow of energy through an ecosystem.

Trophic Levels• Plants are producers and occupy the first trophic level.• Animals that are herbivores are primary consumers and

occupy the second trophic level.• Animals that eat other animals are secondary consumers

or carnivores. They can be subdivided into trophic levels depending on what animals they eat.

• Animals that eat herbivores occupy the third trophic level and are primary carnivores.

• Animals that feed on the primary carnivores are known as secondary carnivores and occupy the fourth trophic level.

• A human can eat a fish that ate a frog that ate a spider that ate an insect that consumed plants for food.

• The sequence of organisms feeding on one another is known as a food chain.

• Omnivores are animals that are both carnivores and herbivores.

Trophic Levels

• If an organism dies the energy in the organic compounds of its body is released to the environment as heat by organisms that decompose the dead body into carbon dioxide, ammonia, and other simple organic molecules. These organisms are called decomposers.

• Decomposers include bacteria and fungi. • The simple inorganic compounds can now be

used by producers to trap energy again.

Ecosystems

Ecological systems

Ecological systems

The food chain

Energy Flow in Ecosystems

• There is about a 90% loss of available energy as we proceed from one trophic level to the next higher level. When the energy in producers is converted to the energy of herbivores much of the energy is lost as heat to the surroundings. The same is true for all the other levels.

Energy flow in Ecosystems

Sun is primary source of energy for most living things.

Higher trophic levels lose ~90% of energy to space due to 2nd law of thermodynamics.

Community Interactions

• Food chains are interwoven into a food web. • In a community the interacting food chains usually result

in a relatively stable combination of populations.• Most ecosystems are not constant. As one population

increases another decreases. This can occur because the there are differences in rainfall throughout the year or changes in the amount of sunlight and in the average temperature.

• Some communities, like tropical rainforests, have large numbers of different kinds of organisms present. Such communities have high biodiversity. Others, like tundra communities, have low biodiversity. If a specific kind of organism is eliminated form a region there is a loss of biodiversity.

Terrestrial Communities• Terrestrial communities are determined primarily by climatic

factors of precipitation patterns and temperature ranges. They are called biomes.

• Biomes include:1. Temperate Deciduous Forest-found in parts of the world

that have a lot of rainfall and cold weather for a significant part of the year. Predominant plants lose their leaves more or less completely during the year. In much of this region the natural vegetation has been removed to allow for agriculture.

2. Grasslands or Prairie-Common in western North America and parts of Eurasia, Africa, Australia and South America. The dominant vegetation is various species of grasses. The rainfall is not adequate to support the growth of dense forests. Most have been converted to agricultural uses.

3. Savanna-Found in tropical regions that have pronounced rainy and dry seasons. Fires during the dry seasons prevent the establishment of forests. Found in Central Africa and parts of South America. Consist of grasses with scattered trees.

Deciduous Forest

Grasslands

Savannah

Terrestrial Communities4. Desert-Very dry areas and are found throughout the

world wherever rainfall is low and irregular. Some are extremely hot and others can be quite cold during the year. Animals avoid the hottest part of the day by staying in burrows or other shaded, cooler areas. Almost no vegetation.

5. Boreal Forest-Also known as taiga-Found in parts of southern Canada and northern US and much of northern Asia. Evergreen trees are the predominant vegetation like spruces and firs. Long, cold winters, abundant rainfall.

6. Temperate Rainforest-The coastal areas of northern California, Oregon, Washington, British Columbia and Alaska. Ample precipitation, fertile soil and mild temperatures result in lush growth of plants like spruce and fir which are evergreens. There are trees as old as 800 years.

Desert

Boreal Forestor Taiga

TemperateRainforest

Terrestrial Communities

• Tundra-North of the boreal forest. Extremely long, severe winters and short, cool summers. The deeper layers of the soil are permanently frozen-permafrost. Very few plants and animals and no trees survive.

• Tropical Rainforests-Primarily in the equator in Central and South America, Africa, parts of southern Asia and some Pacific Islands. High temperatures, daily rain, and many species of plants.

Tropical Rainforest

Tundra

Carbon cycle – essential for the organic compounds

Figure 23.18

Nitrogen cycle – essential for formation of amino acids. Often the limiting factor in terrestrial ecosystems.

Population Characteristics

• A population is a group of organisms of the same species located in the same place at the same time, like the rat population in the sewers of your city, the number of people of New York City, etc..

• The people of the world constitute the human population. A species is the largest population of a particular kind of organism.

• A population usually implies a place and a time.

Populations• A local population is a small portion of a

species and local populations of the same species will show some differences.

• Gene frequency is a difference that populations could show. For example, the genes for tallness in humans is greater in certain African tribes.

The allele for type B blood is not evenly distributed in the world. This map showsthat the type B allele is most common in parts of Asia and has been dispersed to the Middle East and parts of Europe and Africa. There has been very little flowof the allele to the Americas.

Age Distributions

• Another difference in population is its age distribution. If the majority of a population is prereproductive then a “baby boom” should be anticipated in the future. If it is reproductive then the population should be growing rapidly. If it is post reproductive then a population decline should be anticipated.

• Populations can also differ in their sex ratios. (female: male). The larger this ratio is the faster the population grows.

Population Growth

Kenya-large prereproductive population will grow rapidly in the future. US-large reproductive population, low prereproductive. Will continue to grow for a time but will Stabilize in the future. Germany-large post reproductive. Population is beginning to fall.

The Population Growth Curve• There is a tendency for populations to grow if environmental conditions

permit. • The change in in population size over time is known as a population

growth curve. • The change in the size of a population depends on the rate at which new

organisms enter the population compared to the rate at which they leave.• The number of new individuals added to the populations by reproduction per

thousand individuals is called natality. The number of individuals leaving the population by death per thousand individuals is called mortality.

• When a small number of organisms, e.g., two mice, first invade an area there is a period of time before reproduction takes place when the population remains small and relatively constant. This is called the lag phase.

• The exponential growth phase is when active reproduction is occurring and the mortality rate is low because the population is young.

• Eventually conditions such as food, water, or nesting sites will be in short supply, or predators or disease may kill many individuals. Then the number of individuals entering the population by reproduction or immigration will come to equal the number of individuals leaving it by death or migration and the population size becomes stable

• During the stable equilibrium phase there is a decrease in natality and an increase in mortality.

Population growth curve

Natality – added to population by reproduction

Mortality – leaving population by death.

First introducedNatality and mortality low.

High natality Natality equals mortality

Limiting Factors to Human Population Growth• The curve of population growth over the past several thousand

years for humans shows that the human population remained low and constant for thousands of years but has increased rapidly in the past few hundred years.

• When Columbus discovered America the native American population was about 1 million and was at near the carrying capacity, the maximum that the area could support.

• Today the population of the US and Canada is about 300 million people. This tremendous increase in the carrying capacity is due to technological changes and the displacement of other species. Much of it is due to the removal of diseases, improvement in agricultural methods, and replacement of natural ecosystems with artificial agricultural ecosystems.

• However, there are limits, since we cannot increase beyond our ability to get raw materials and energy or our ability to dispose of waste products or the other organisms with which we interact.

A number of factors in the environment, such as food, oxygen supply, diseases, predators, and space, determine the number of organisms that can survive in agiven area-the carrying capacity of that area. The environmental factors that limitpopulations

Presently the human population is growing at ~75 million people per year. All animals reach a carrying capacity. Exponential

growthThe Plague

The number of humans doubled from A.D. 1800 to 1930 (from 1-2 billion)It is projected to double again by the year 2025.

Practice Exercises

• P. 508-509 Applying the Concepts:

# 1, 3, 4, 6, 7, 9, 10, 11, 12

New Book:

p. 578-579 # 1, 2, 3, 4, 6, 9, 10, 12

Summary• Ecology – study of relationships between

organisms and environment. Biotic-living, abiotic-nonliving.

• The smallest living unit is the individual organism. Populations are groups of organisms of the same species. Communities are interacting groups of populations of different species. An ecosystem is all the interacting organisms in an area and their interaction with their abiotic surroundings.

• Those organisms that trap sunlight from inorganic material for photosynthesis are called producers, the first trophic level, like green plants, algae, and cyanobacteria. They convert sunlight energy into the energy contained within the chemical bonds organic compounds. Consumers obtain energy in the form of organic matter.

• All animals are consumers. Each time the energy enters a different organism it is said to enter a different trophic level. Animals that are herbivores are primary consumers and occupy the second trophic level. Animals that eat other animals are secondary consumers or carnivores. Animals that eat herbivores occupy the third trophic level and are primary carnivores. Animals that feed on the primary carnivores are known as secondary carnivores and occupy the fourth trophic level. The sequence of organisms feeding on one another is known as a food chain. Omnivores are animals that are both carnivores and herbivores.

• The energy in the organic compounds of dead organisms is released to the environment as heat by decomposers that turn them into carbon dioxide, ammonia, and other simple organic molecules and include bacteria and fungi. These can now be used by producers to trap energy again.

• There is about a 90% loss of available energy as we proceed from one trophic level to the next higher.

• Biomes :temperate deciduous forest-cold, rainy, many trees, loss of leaves, marked seasons; Grasslands-medium rain, vegetation mostly grass; savannah-rainy and dry seasons, little vegetation; desert-very dry, almost no vegetation; taiga or boreal forest-long cold winters, rainfall; temperate rainforest-mild T, rain, evergreen trees; tundra-very cold, little vegetation; tropical rainforest-warm, rainy, many plants.

• Carbon cycle-CO2 from atmosphere intake by plants, photosynthesis converts it to organic materials and O2. Organic materials are taken in by herbivores and use it for energy and to grow through respiration, and this produces CO2 which It is returned to the atmosphere.

• Nitrogen cycle-N2 Bacteria convert it to compounds that plants can use and animals obtain it from plants. It is later returned to atmosphere after decomposition of living matter or taken up by plants again.

• Population growth based on age distribution and sex. More females-more reproduction. More reproductive age-positive current growth, more post reproductive age-negative growth. More prereproductive age-future positive growth.

• Initial lag phase, then natality greater than mortality- exponential growth phase. Later natality equals mortality stable equilibrium phase.

• Carrying capacity-the maximum population an area can hold. Can be increased by technological advances. The world as a whole is now in an exponential growth phase.