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TESC 211 The Science of Environmental Sustainability Autumn 2011UWT What about non-feeding relationships between species? Mutually supportive relationships •Symbiosis •Pollinator-plant Competitive relationships •Habitat •Niche •Resource Partitioning •Competitive exclusion principle The concept that relationships between species may be of mutual benefit is known as mutualism. e.g. Honey bees and flowering plants In some cases the mutualistic relationship has become so close that one species cannot survive without the other. e.g. lichens are composed of an algae (producer) living in symbiosis (close union) with a fungus (consumer) In parasite-host relationships the symbiotic relationship may not be beneficial to both species. These non-feeding relationships may improve the overall functioning of the ecosystem. e.g. Worms aerate and return nutrients to soil which is of benefit to plants. Predators targeting weaker or sick members of a species may benefit the population as a whole by keeping it healthy. Competition between species is limited as a result of each species being specialized and adapted to its own habitat and niche. Habitat refers to the place a species is adapted to live. Different habitats support different species. e.g. we don’t get every species in every place Even within a given habitat competition is limited as each species occupies its own niche. A species ecological niche describes amongst other things: • what it consumes • grubs versus nectar •where it feeds • Different species of warblers have different foraging heights (Warblers live in the spruce forests of Maine) •When it feeds • nocturnal versus diurnal By adapting to particular ecological niches species that occupy the same habitat limit competition. This adaptation to each others presence is an example of resource partitioning and is of benefit to all species present in an ecosystem. However, some competition is unavoidable. e.g. All green plants require sunlight, water and nutrients If two species compete directly in many respects (often occurs with introduced species) one of the two generally perishes. “competitive exclusion principle” also known as Gause’s Law. This was formulated by Georgii Gause by studying species of Paramecium. He observed that under constant conditions one species of Paramecium would always exclude another. We can divide abiotic factors into conditions and resources. Conditions can be defined as: “abiotic factors that vary in space and time but are not used up or made unavailable to other species” e.g. temperature, salinity, wind etc Abiotic resources can be defined as: “any abiotic factors that are consumed by organisims” e.g. Water, nutrients, oxygen, space When we grow organisms in the lab in such away that we keep all factors constant except one that we vary we discover that for every factor there is an optimum value. The range of the factor over which any growth occurs is called the “range of tolerance” for that factor. The values at the extreme ends of the range of tolerance are referred to as the limits of tolerance. Between the optimal range and the limits of tolerance are zones of stress where growth is poor. Often this is referred to as “Law of limiting factors” or “Liebig’s Law of minimums” (Justus von Liebig) The population of a species will be greatest where all factors are optimal and will decrease when one or more are not. The previous discussion does not describe the possibility of synergistic effects. i.e. what happens when we have several factors at suboptimal values? Often we find the synergistic effect can be greater than the sum of the parts. An additional factor that may constrain a species is a physical barrier. Examples include: • Ocean • Desert • Mountain range These physical barriers limit the range in which we will find certain species. Physical barriers are overcome when Human’s transport a species. The introduced species may disrupt the ecosystem into which it is introduced. e.g. Starlings, rabbits, cane toads Alternatively Human’s may create artificial barriers which restrict normal movement of a population. e.g. dams (migratory fish), roads, forest clearings Sequim WA We have explained in great detail how matter is cycled through food chains and webs. What other processes are occurring to cycle materials in ecosystems? How have humans impacted these processes (if at all)? Elements and compounds in ecosystems are continually cycled the biosphere, lithosphere, atmosphere and hydrosphere through “biogeochemical cycles”. These cycles are driving either by gravity or solar energy. Of particular importance are the: • carbon cycle • nitrogen cycle • phosphorus cycle • sulfur cycle • hydrological (water) cycle The Earth has a fixed supply of water. This supply is collected, transported and purified by the hydrological cycle. The are large reservoirs of water in the atmosphere and the hydrosphere, predominantly the oceans. Transportation of water is driven by gravity and solar energy and involves by three major processes. • Evaporation • Precipitation • Transpiration Evaporation is the transformation of liquid water into the vapor phase. It is the mechanism by which water is transported from the hydrosphere to the atmosphere. Does this process require in input of energy? If so where does this energy come from? Over land 90% of evaporation occurs from the surfaces of plants (transpiration) and from the soil. Gravity draws some of the water back from the atmosphere to the Earth’s surface as rain, snow, sleet and dew. This process is called precipitation. • This is a release of gravitational potential energy Most precipitation falling on terrestrial ecosystems becomes surface runoff which eventually flows back into the hydrosphere. Some water falling on terrestrial ecosystems is converted to ice and stored in Glaciers, some sinks through permeable rock and soil and is stored as ground water in aquifers. Through out the hydrological cycle many processes purify water. • Evaporation and precipitation as a natural distillation process. • Water flowing above ground is filtered and partially purified by natural chemical and biological processes. The hydrological cycle can be considered as: “a cycle of natural renewal of water quality” It is worth noting that water is a powerful solvent. • Agent for transporting nutrients and pollutants Human activities have seriously modified the hydrological cycle. • Clearing of vegetation for agricultural, industrial and residential use. • Increases run-off (transportation of matter) • Reduces ground water recharge • Accelerates erosion • Increases risk of flooding Human activities have seriously modified the hydrological cycle. • Withdrawal of large amounts of freshwater from streams, lakes and underground sources • Only ~0.024% of the Earth’s water is accessible to humans and other species as liquid freshwater. • The rest is too salty, stored as ice or too deep underground. Carbon is the basic building block of the lipids, carbohydrates, DNA , proteins and other organic molecules common to all organisms. The carbon cycle serves to circulate carbon through the biosphere, atmosphere, lithosphere and hydrosphere. The carbon cycle is based upon the circulation of inorganic carbon dioxide. Carbon dioxide is a minor component of our atmosphere (0.038%) and is also dissolved in water. Terrestrial producers remove carbon from the atmosphere. Aquatic producers remove carbon from water. The producers use carbon dioxide to produce glucose via photosynthesis which is then further converted to the desired organic molecules. Consumers and decomposers (as well as some oxygen consuming producers) carry out respiration. Respiration breaks down complex organic molecules producing water and carbon dioxide Humans affect the carbon cycle by adding carbon dioxide to the atmosphere. • Through clearing of vegetation faster than it can grow back •Through the burning of “biomass” and fossil fuels