Ecological Succession

Ecological succession Ecosystem Stability The interrelationships and interdependencies of organisms affect the development of stable ecosystems. The types of animal communities found in an ecosystem are dependent upon the kinds of plants and other producer organisms in that ecosystem. Succession The environment may A Typical New York State Succession be altered in substantial ways through the activities of humans, other living things, or when natural disasters occur, such as climate changes and volcanic eruptions. Although these changes are sometimes occur very quickly, in most cases species replace others gradually, resulting in longterm changes in ecosystems. These gradual long-term changes in altered ecosystems are called ecological successions. Ecosystems tend to change with time until a stable system is formed. The type of succession, which occurs in an ecosystem, depends upon climatic and other limitations of a given geographical area. Pioneer organisms are the first organisms to reoccupy an area, which has been disturbed by a disruption. Typical pioneers in a succession include grasses in a plowed field or lichens on rocks. These pioneer organisms modify their environment, ultimately creating conditions which are less favorable for themselves, but establishing conditions under which more advanced organisms can live. Over time, the succession occurs in a series of plant stages, which leads to a stable final community, which is very similar to the plant community, which originally existed in the ecosystem. This final stable plant community is called a climax community. This community may reach a point of stability that can last for hundreds or thousands of years. A Pond Succession Sequence It has been observed that when natural disasters occur, such as a floods or fires, the damaged ecosystem is likely to recover in a series of successional stages that eventually result in a stable system similar to the original one that occupied the area. A Typical New York State Succession This chart represents a typical succession, which is observed in New York State. The annual grasses represent the pioneer or first organisms in this succession. The beech-maple forest would represent a typical Northern New York climax community. The climax community will last hundreds or thousands of years unless again disrupted. A forest containing oak and/or hickory trees would be a more typical Southern New York climax community. Biodiversity Biodiversity As a result of evolutionary processes, there is a diversity of organisms and a diversity of roles in ecosystems. Biodiversity refers to the differences in living things in an ecosystem. Increased biodiversity increases the stability of the ecosystem as it provides for more genetic variation among species. A great diversity of species increases the chance that at least some living things will survive in the face of large changes in the environment. The Need for Biodiversity Human Influences on Biodiversity When humans alter ecosystems either by removing specific organisms, serious consequences may result. Human beings are part of the Earth’s ecosystems. Human activities can, deliberately or accidentally, change the equilibrium in ecosystems. Humans are destroying other species as a result of population growth, consumption, and technology. Human destruction of habitats through direct harvesting, pollution, atmospheric changes, and other factors is especially threatening current global biodiversity. An example of a human activity, which has decreased biodiversity, is the use of monoculture in modern agricultural practices. Monoculture involves planting one variety of a species over a huge area. This leaves this area more vulnerable to predation or disease and the loss of many or all species. Uses of Biodiversity In addition to the aesthetic beauty added to the world by many different organisms, biodiversity also ensures the availability of a rich variety of genetic material that may lead to future agricultural or medical discoveries with significant value to humankind. As diversity is lost, potential sources of these materials may be lost with it. Biotic Vs. Abiotic Abiotic Factors Abiotic factors are those non-living physical and chemical factors, which affect the ability of organisms to survive and reproduce. Abiotic factors vary in the environment and determining the types and numbers of organisms that exist in that environment. Factors which determine the types and numbers of organisms of a species in an ecosystem are called limiting factors. Many limiting factors restrict the growth of populations in nature. An example of this would include low annual average temperature average common to the Arctic restricts the growth of trees, as the subsoil is permanently frozen. Some Abiotic Factors • • • • • • • Light intensity Temperature range Type of soil or rock pH level (acidity or alkalinity) Water availability Dissolved gases Level of pollutant Biotic Factors Some Biotic Factors • • • Parasitism Disease Predation Biotic factors are all the living things or their materials that directly or indirectly affect an organism in its environment. This would include organisms, their presence, parts, interaction, and wastes. Factors such as parasitism, disease, and predation (one animal eating another) would also be classified as biotic factors. Carrying Capacity Carrying capacity is the maximum number of organisms the resources of an ecosystem can support. The carrying capacity of the environment is limited by the available abiotic and biotic resources (limiting factors), as well as the ability of ecosystems to recycle the residue of dead organisms through the activities of bacteria and fungi. Energy flow Feeding Relationships Energy flows through ecosystems in one direction, typically from the Sun, through photosynthetic organisms including green plants and algae, to herbivores to carnivores and decomposers. Green plants and algae are called autotrophs or producer organisms, as they capture solar energy to make sugars in the process of photosynthesis. Herbivores or primary consumers use the producer organisms to provide them with their food. Carnivores are secondary consumers as they eat the primary consumers as their source of food. Some organisms are capable of functioning as primary consumers (eating plant material) and as secondary consumers (eating animal material). These organisms are called omnivores. Humans are examples of omnivores. All consumers are examples of heterotrophic organisms, as they can not make their own food using the sun, but depend upon the ingestion of other organisms for their nutrition. Food Chains If an ecosystem is to be self-sustaining, it must contain a flow of energy. One way of representing the flow of energy through the living components of an ecosystem is through the use of a food chain. A food chain indicates the transfer of energy from producers through a series of organisms, which feed upon each other. A Food Chain The algae and floating plants are the producers in this food chain. The aquatic crustaceans are the primary consumers, which eat the producers. Fish are secondary consumers eating the primary consumers. Note that the arrows in the food chain point to the organisms, which are doing the eating. Thus, the arrows in the food chain represent the flow of energy through the ecosystem. A food chain may also contain third level or other consumers as indicated by the raccoons in this food chain. Food Webs In a natural community, the flow of energy and materials is much more complicated than illustrated by any one food chain. A food web is a series of interrelated food chains, which provides a more accurate picture of the feeding relationships in an ecosystem, as more than one thing will usually eat a particular species. A Food Web Energy flow in a food web also starts with the producer organisms through the various levels of consumer organisms as in a food chain. Energy Pyramids An Energy Pyramid An energy pyramid provides a means of describing the feeding and energy relationships within a food chain or web. Each step of an energy pyramid shows that some energy is stored in newly made structures of the organism, which eats the preceding one. The pyramid also The picture at the left is an energy pyramid. Producer organisms shows that much of represent the greatest amount of living tissue or biomass at the bottom the energy is lost of the pyramid. The organisms, which occupy the rest of the pyramid, when one organism in belong to the feeding levels indicated in each step. On average, each a food chain eats feeding level only contains 10% of the energy as the one below it, with another. Most of this the energy that is lost mostly being transformed to heat. energy, which is lost, goes into the environment as heat energy. While a continuous input of energy from sunlight keeps the process going, the height of energy pyramids (and therefore the length of food chains) is limited by this loss of energy. Material cycles Water Cycle The atoms and molecules on the Earth cycle among the living and nonliving components of the biosphere. Some of the water molecules, which are used in photosynthesis, are returned to the environment. The change of water from the liquid to the gas state is called evaporation, while the water lost to the atmosphere by the activities of plants is referred to as transpiration water loss. This water vapor eventually condenses to form clouds, and is returned to the earth as precipitation. This process is called the water cycle. The processes of cell respiration and excretion also release some water to the environment as well. The Water Cycle Carbon-Oxygen Cycle The Carbon-Oxygen Cycle Carbon dioxide molecules are used in the process of photosynthesis to form energyrich organic sugar compounds. These carbon dioxide molecules are returned to the environment by the process of cell respiration, when the energy from these compounds is eventually released by cells. Some carbon is also returned to the environment by the decomposition of dead organisms. Oxygen is required by many living things to release the energy in their food in the process of aerobic cellular respiration. Oxygen is released to the environment as a waste product of the process of photosynthesis. Other compounds, such as nitrogen, are cycled in the environment when organisms synthesize proteins from simpler compounds and then return these nitrogen compounds to the environment when they die and decompose. Role of Decomposers The number of organisms any environment can support is the carrying capacity of the environment. Carrying capacity is limited by the available energy, water, oxygen, and minerals, and by the ability of ecosystems to recycle the remains of dead organisms through the activities of decomposers such as bacteria and fungi. Organism Relationships Feeding Relationships Organisms may interact with one another in several ways. One example of an organism interaction is that of a producer/consumer relationship. A producer is any organism capable of making its own food, usually sugars by photosynthesis. Plants and algae are examples of producers. A consumer is any organism, which eats another organism. Several different types of consumer organisms exist. A herbivore is a consumer, which eats primarily plant material. A deer is an example of a herbivore. A carnivore consumes primarily animal material. An omnivore eats both plant and animal matter. Humans are examples of omnivorous organisms. A predator is a type of carnivore that kills its food. The organism the predator feeds upon is called its prey. A wolf and rabbit would provide an Scavengers Feeding example of a predator/prey relationship. Scavengers feed upon organisms that other organisms have killed. A crow feeding off dead carrion in the highway would be an example of scavenger in this instance. Symbiotic Relationships The cartoon above represents a typical situation where vultures Close living associations are are acting as scavengers feeding on a dead rhinoceros. called symbiotic relationships. Types of Symbiosis Parasitism is an example of such a Parasitism: the parasite benefits at the expense of the host relationship. In this Mutualism: both organisms benefit from the association situation, the parasite Commensalism: one organism is benefited and the other is unharmed feeds upon the tissues or fluids or another organism, but usually does not kill the organism it feeds upon, as this would destroy its food supply. The organism the parasite feeds upon is called the host organism. An example of this sort of relationship would be fleas on a dog or athlete's foot fungus on a human. Other Relationships Some organisms such as certain pathogenic bacteria may cause disease in other organisms. Decomposer organisms use the energy of dead organisms for food and break them down into materials, which can be recycled for use by other organisms. Bacteria of decay and many fungi are examples of decomposer organisms.