Connecting LinksChapter 1 Unit 1 Sustainability of Ecosystems

Key concepts

• The ultimate source of energy for most ecosystems

• Conversion of radiant energy to chemical energy

• Channeling of energy through ecosystems

• Position of an organism in the food chain may determine mass and population size

• Human consumption of large part of all radiant energy converted into living material

• Eating food is one of the main activities of all animals

• What are some examples• Eating food is really about

material and energy transfer from one organism to another

• This transfer is the basis of a food chain

• Energy flows through living systems by being transferred from one organism to another

• The original source of the energy for food is the Sun

• Radiant energy is captured by green plants, algae, and some bacteria through photosynthesis and is used to make food

• Many of our environmental problems are caused by disrupting the energy flow among organisms e.g. …

Capturing Energy from the Sun

• Energy is the common denominator for growth, reproduction, and sustaining life

• Ecology is the study of all the interactions that occur within the biosphere

• An ecosystem is all the interacting parts of a biological community and its environment; a group of living organisms and their abiotic environment, forming a self-regulating system through which energy and materials flow

• Some ecosystems are; forest, lake, pond, ocean, desert

Capturing Energy from the Sun

• Photosynthesis involves the capture of sunlight by green plants and the fixation of atmospheric carbon into carbohydrate molecules i.e chemical energy

• Energy flows through an ecosystem from one species to the next as herbivores eat plants and carnivores eat the herbivores

Capturing Energy from the Sun

• Chemosynthesis is a process of energy transfer in the absence of sunlight whereby bacteria living around hot thermal vents on the sea floor use chemical compounds to produce sugars. The bacteria then use the sugars as energy

• Since green plants convert radiant energy into chemical energy for ecosystems, they are called producers and represent the first feeding level in the ecosystem

Capturing Energy from the Sun• Rabbits, deer, some mice , and herbivorous

insects that all eat plants are called primary consumers

• Animals that feed on the plant eaters are called secondary consumers

• Ecosystems require a continual input of energy from the Sun

• Green plants produce more energy per unit land area than animals so in an agricultural ecosystem such as a field of corn or wheat, only a fraction of the energy produced is transferred when the crops are eaten

• This is analogous to when gasoline is combusted, all the energy in the chemical bonds is not transferred to the wheels of the car.

Feeding or Trophic levels

• Eosystems are made up of several trophic levels. Trophic means “nourishment”

• Producers→Primary Consumers→Secondary Consumers→Tertiary Consumers

• 1st tl →2nd tl → 3rd tl →4th tl where tl means trophic level

Trophic Levels• Most of the energy at each trophic level is

used by the organism simply to stay alive• Energy is required to feed itself, to grow, to

move, to reproduce, etc• Only a small fraction of the energy is stored

by the organism as body tissues.• It is this fraction that is available as potential

food for consumers at the next trophic level• Scientists estimate that between 5 and 20% of

the energy at one trophic level is available for the subsequent level. As a rough average, 10% is considered a reasonable estimate

Trophic Levels

• Consider the following example• 100 kJ------------------10kJ---------------------1kJ-------------------0.1kJ

• Producers------Prim Con--------2nd Con----------3rd Con

Trophic Levels• The remaining 90% goes into thermal energy and

waste.• Organisms that die without being eaten still maintain

energy in their tissues.• Scavengers such as vultures, bald eagles, ravens,

hyenas, certain species of ants and beetles are consumers which feed on the bodies of dead larger animals.

• Detritivores are organisms such as crabs, earthworms, wood beetles, carpenter ants, which feed on the dead bodies of smaller dead animals, dead plant materials, and animal dung. They include decomposers such as bacteria and fungi which consume any remaining dead plant and animal matter.

• Decomposers break down the cells and extract any remaining energy

Trophic levels

• Detritivores feed at every trophic level and comprise their own food chains.

• Earthworms and beetles feeding on cow dung become part of the food chain for birds and other organisms

Pyramid of Numbers

• Generally speaking, the higher up the food chain you go, the smaller the total numbers of each species e.g. hawks eat snakes which in turn eat mice. There are more mice than snakes and more snakes than hawks. Why might this be so?

• Consider availability of energy• This leads to the formation of a

pyramid of numbers

Pyramid of numbers

Trophic Levels

• There are cases where for example a thousand pine bark beetles can feed on one tree. So some smaller organisms can feed on larger ones. Pyramids of numbers have limitations- they do not account for the sizes of the individual organisms.

• Another way of measuring energy flow in an ecosystem combines the number with the size. Biomass refers to the total dry mass of a given population of organisms

Pyramid of Biomass

• This pyramid graphically represents the decrease in biomass while moving up the trophic levels. See text p.16

Trophic levels• Exceptions to this upright pyramid do

exist. One example is a larger biomass of zooplankton (microscopic animals) feeding on a smaller biomass of phytoplankton (microscopic algae-plant organisms) in an ocean ecosystem. See text p.16

• The ecosystem does not crash because of the faster growth and reproductive rate of the algae. This enables sustainability of the larger biomass of zooplankton.

• Another example involves fish and the zooplankton they feed on.

Trophic Levels

• In addition to the pyramid of numbers and the pyramid of biomass, a pyramid of energy flow can also be used to represent energy flow in an ecosystem. It represent the total chemical energy flowing through each trophic level. Since energy flow diminishes moving up a food chain, these pyramids are always oriented in an upright position.

Trophic Levels

Secondary Consumers

Primary Consumers

Producers

Trophic Levels

• If ,as scientists estimate, only 10% of the energy is transferred to the next trophic level, then, less and less energy is available to the organisms higher up in the food chain. For this reason, food chains rarely have more than four links.

Populations

• Refer to text example p. 18 Killer whales and sea otters

• This example illustrates how population changes in one part of a food web impact populations in other parts of the web.

• A food web is a set of interactions and interconnections among different food chains

Carrying Capacity

• This refers to the largest population of a species than an environment can support.

• Factors determining carrying capacity:– Materials and energy– Food chains– Competition– Density

Carrying Capacity• Materials and energy refer to the supply of water,

carbon, and other essential materials as well as energy from the Sun

• Food Chains refer to the limitations placed on a population by the available food supply and by predation

• Competition refers to the competing demands for resources such as food, water, mates, and space among individual organisms. Two types of competition are intraspecific within species and interspecific or among different species

• Density refers to the need for space. Population density means how many individuals can live in an area at one time. Overcrowding may lead to stress, disease, aggression, neglect of offspring etc.

• Factors which increase in significance as the population grows are density dependent.

• Other factors can limit a population regardless of size; they are density independent e.g floods, forest fires

Feeding People

• Different ecosystems have differing levels of productivity. A tropical rainforest ecosystem is considerable more productive than desert scrub or extreme desert.

• Productivity refers to the average amount of new plant biomass produced annually per unit area.

Feeding People• Plants need water and carbon dioxide

to make food and to grow.• They also need nutrients like nitrogen

and phosphorus to grow. The rate of growth is affected by temperature. Warmer conditions enable faster growth and greater biomass.

• Using irrigation, fertilizers, and genetically-modified (gm) crops can improve productivity of some ecosystems but they have downside risk. What might be some examples of this risk?

Feeding People• Clearing tropical rainforest for

agriculture and cattle ranching has adverse consequences. What might some of these be?

• Think in terms of erosion, loss of habitat, biodiversity

• When trees are cut in a tropical rainforest, thin poor soil remains since most of the biomass is in the trees. Detritivores quickly consume most of the dead and waste materials on the forest floor. The soil washes away by heavy rainfall.

• Refer to figure 1.23 in your text. Note that the longer the food chain, the smaller the amount of energy available to humans at the top of the chain. Also most of the world’s population have a diet consisting of mostly grain.

• Agriculture aims to produce short, simple food chains with usually no more than two links i.e plants to humans. Single crops such as wheat, corn, or rice are grown on huge tracts of land. This is referred to as monoculture.

• Natural ecosystems tend to have hundreds of species interconnected in complex food webs.

• When we grow food, insects, birds, and other organisms feed on the crops. We consider them pests and we impact their population by providing a food supply or by chemicals to control insects.

• Pesticides are poisonous chemicals farmers use to minimize crop damage. Although they target insects, they often have unintended consequences

• Referring to the graph on p. 33, note that the human population has surpassed 6 billion and continues to grow. The population growth has been attributed to a decline in the mortality rate due to improved health care, sanitation, water supply and increased food production. As the population grows, energy flow in ecosystems is impacted. Burning forests, draining wetlands, paving over land for highways, building golf courses and residential subdivisions on fertile land, damming rivers for energy mega projects, overgrazing land with livestock collectively reduce plant biomass and energy flow. It has been estimated that humans either use, convert, or divert more than 20% of the Earth’s biomass.