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A Local Ecosystem Part 2 Each local aquatic or terrestrial ecosystem is unique examine trends in population estimates for some plant and animal species within an ecosystem Populations of organisms do not remain at a constant level within an ecosystem. Many factors may affect their numbers. o When the same species is found in an ecosystem year after year in approximately the same numbers, scientists say the population is stable or in balance. o Sometimes the numbers in a population increase dramatically; we refer to this as a population explosion. o Population numbers may also decline. Disease, predation, competition from other species, and human activities can all contribute to the decline and possible extinction of an organism in an ecosystem. Grey Mangrove forest at Homebush Bay: o As the water level rose, the amount of mangrove seedlings decreased, but the amount of semaphore crabs increased o As the water level reduced, the amount of mangrove seedlings increased, but the amount of semaphore crabs decreased o This pointed out that mangrove seedlings do not prefer to be covered in water, while crabs do o Summarise one other population trend from the textbook, p19. 1 outline factors that affect numbers in predator and prey populations in the area studied o The amount of food available o The salinity of the water o The amount of water available o The reproductive cycles of both prey and predator affect their numbers. Large numbers of young prey may be followed by an increase in predator numbers. The prey are eaten, their numbers decline, and numbers of predators then also decrease. o There is often competition between predators for the same prey. For example, cormorants and gannets compete with large fish for the smaller fish they all prey on. 2 o Diseases can affect both predators and/or prey. If prey are affected, then the food supply for predators will be less and they will also decline in number. If predators are affected, the numbers of prey will increase. o Seasonal migrations of predators or prey will affect populations. When prey are abundant, some predators might move into an ecosystem to take advantage of the abundance. identify examples of allelopathy, parasitism, mutualism and commensalism in an ecosystem and the role of organisms in each type of relationship Allelopathy: o This is the production by a plant of specific chemicals (allelo-chemicals) which inhibit the growth of other plants around it. o The example studied was the Casuarina. Its leaves contain allelo-chemicals, so as they dropped to the floor, they released the chemicals, preventing the growth of other plants in the area. 3 Parasitism: o This is a relationship between two organisms where one benefits at the expense of the other organism. o The example studied was the pimple wasp. It lays its eggs on the leaves of the mangrove. The larvae eat through the leave when they hatch and the leaf is damaged. Symbiosis o Symbiosis is a type of interaction between organisms where two different species live together in a close association. The association benefits at least one of them, and the other is not disadvantaged. The two common types of symbiosis are commensalism and mutualism. Mutualism: o A relationship between two organisms where both of them benefit. o The example studied was lichen. This consists of a fungus and an alga joined together. The fungi provides structure and the alga provides food. Commensalism: o A relationship between 2 organisms where only one benefits, and the other gets no harm and no benefit. o The example studied is the golden orb-weaving spider and the dewdrop spider. The weaving spider makes a web, and catches its prey with it. It leaves scraps behind. The dewdrop spider eats the leftovers. describe the role of decomposers in ecosystems Bacteria and fungi secrete digestive enzymes that break down detritus (dead organic matter) into soluble organic molecules such as sugars, and eventually into inorganic molecules such as carbon dioxide and nitrogen. o Decomposers are the rubbish cleaners of the ecosystems o They feed on the left overs of other organisms, dead organisms and decaying organisms and their wastes. o They enable the materials of decomposition available to plants o They keep the biomass in circulation. 4 explain trophic interactions between organisms in an ecosystem using food chains, food webs and pyramids of biomass and energy Trophic interactions are feeding relationships between organisms o A FOOD CHAIN represents the flow of energy from one living thing to the next. o Food chains start with t h e s u n t h e n t h e producers (plants), which are eaten by herbivores, which are eaten by carnivores. o The first consumer is the organism that eats the first other organism. It is usually a herbivore. Food Webs o Food webs are a complex set of interacting food chains within an ecosystem o Animals are consumers. An organism that feeds on plants is a first-order consumer. An organism that feeds on a first-order consumer is called a secondorder consumer, and so on. The level occupied by a consumer in a food chain is referred to as a feeding or TROPHIC level. First-order consumers occupy the first trophic level; second-order consumers occupy the second trophic level, and so on. 5 o Ecosystems are composed of food webs, not just food chains. o At every step of a food chain, energy is lost o It is lost as heat, and waste o This is represented in an energy pyramid, as the lowest level is the biggest, and the levels shrink as they go up o At every step of the food chain, biomass (mass of organisms) is lost o Biomass is lost as undigested material and wastes o This is also shown in a biomass pyramid o Biomass pyramids and energy pyramids are usually similar in ecosystems Biomass Biomass is the amount of living material in an organism or group of organisms at any one time. The amount or mass of living plant material produced by photosynthesis in an ecosystem is the plant biomass. Biomass is an estimate of the amount of matter in a given population of organisms. Biomass for different trophic levels is compared in a biomass pyramid. A biomass pyramid shows how the quantity of matter in living things changes along a food chain. 6 Biomass Pyramid Energy Pyramid Energy is lost as heat and waste. 7 define the term adaptation and discuss the problems associated with inferring characteristics of organisms as adaptations for living in a particular habitat o An adaptation is a feature of an organism that makes it well suited to its environment and lifestyle. o An adaptation may be structural – a physical characteristic relating to the structure of an organism’s body, e.g. skin colour, shape and body covering. o An adaptation may be physiological - related to the way the organism functions, e.g. (e.g., making venom, secreting slime, being able to keep a constant body temperature). o An adaptation may be behavioural - how an organism responds to its environment. o Adaptations help and organism to survive and reproduce in an ecosystem. identify some adaptations of living things to factors in their environment identify and describe in detail adaptations of a plant and an animal from the local ecosystem Adaptations are inherited characteristics. They are the result of natural selection. When looking for adaptations in organisms, care needs to be taken that the characteristics are in fact inheritable, and not the result of a particular individual’s life history. Problems associated with inferring characteristics of organisms include: o If you do not know the environment an organism lives in, then saying a characteristic is an adaptation is just guesswork o Sometimes, organisms gain features that are advantageous to its survival, but are a result of the organism’s live experience. This is not an adaptation, as adaptations are always genetically based Case study 1: Mangroves o Mangroves form woody plant communities in warm, shallow tidal water over more than half of the Australian coastline. o Mangroves are found on sheltered muddy shores and along estuaries. Depending on the conditions and the species, they range from 2 m high shrubs to 30 m high trees. Support and movement Mangroves are upright woody plants. They are anchored by complex root systems in the shifting environment of tidal mud flats. They have vertical anchor roots to which are attached spreading cable roots. Together these form a dense mass which helps stabilise the mud. Some mangroves support themselves on ‘stilt’ roots that lift the plant out of the salty water. 8 Stilted Roots o Stilt roots have numerous functions one of the most important one of the most important one is to uphold the mangrove and ensure its growing space. o Another important ability of stilt roots is to allow the exchange of gas in oxygen-poor sediments. The arc-shaped prop roots often can be found with a huge amount of lenticels that allow gas exchange in the oxygen-poor soils. (A lenticel is a porous tissue consisting of cells with large intercellular spaces in the periderm of the secondarily thickened organs and the bark of woody stems and flowering plants. It functions as a pore, providing a pathway for the direct exchange of gases between the internal tissues and atmosphere through the bark, which is otherwise impermeable to gases.) o Stilt roots bind sediments and ensure sustainable coastal protection by sediment accumulation and counteract coastal erosion. This prevents the tree from being uprooted. 9 Pneumatophores Pneumatophores are erect roots that are some form of upward appendage or extension of the underground root system. Because these roots are exposed at least part of the day and not submerged underwater, the root system can obtain oxygen in an otherwise anaerobic substrate. Control of water balance Mangroves are halophytes (salt-tolerant plants). The water available to them is salt water with a high ion concentration. They control their salt level in three ways: o accumulation: their cells maintain higher than normal concentrations of cell solutes o secretion: some mangroves have salt glands on their leaves which actively secrete salt o exclusion: some mangroves use energy to excrete salt. Control of internal temperature o Mangrove leaves have a thick cuticle and are hard and leathery. These features help to control water loss and prevent wilting in hot weather. In dense mangrove swamps the thick canopy of leaves helps maintain a lower temperature in the lower layers. 10 Obtaining light o Mangroves are the dominant plant in their community. The shape of the plant and arrangement of leaves ensure abundant light is available for photosynthesis. o The leaves are dark green because they are rich in chlorophyll. The leaves high on the plant are angled and those lower down are horizontal to best capture sunlight. Reproduction o Mangroves have flowers and, following pollination and fertilisation, fruits containing one seed develop. These seeds begin germination before they drop from the parent plant. The seeds are buoyant and dispersed by the tide. Their initial development, particularly of the root system, ensures the new plant can rapidly anchor itself and grow rapidly once it is deposited in the mud. 11 Mangrove Identification in the Tweed: There are 7 species of mangroves in the Tweed Estuary. The most common species are: 12 Assignment. o Obtain photographs of the above mangroves and there leaves. o Identify the type of water balance they use. Case Study 2 – Kangaroos Members of the genus Macropus are all physically very similar. Few species are solitary and most congregate in groups or mobs. Kangaroos are widespread across Australia. They are all grazing herbivores that feed on grasses and herbs. Support and movement o Kangaroos have an internal bony skeleton. Their well-muscled hind legs are far larger than their forelegs. Only the hind legs are used when the animal is travelling at high speed. This method of bounding along is more efficient in terms of energy use when compared with animals which run on all four legs. o The long tail of the kangaroo is a useful structure. It is used as a balancing counterweight when bounding, as an extra limb when hopping, and it helps the kangaroo to remain upright when standing still. Control of water balance o Kangaroos in arid areas, such as the red kangaroo and euro, can survive for long periods without drinking water, provided there is sufficient green plant material available. Kangaroos reduce water loss by sweating only during exercise. When they stop moving, sweating stops. Control of body temperature o When the weather is hot, euros may lick their forelimbs where the blood vessels run close to the surface and heat is lost from the body. It is thought that the evaporation of the saliva has a cooling effect. 13 Reproduction o Kangaroo population numbers are controlled through reproduction. Under good environmental conditions numbers can increase rapidly, because female kangaroos can be almost continuously pregnant when adult. They mate again directly after giving birth. If the mother is still suckling her newborn young, the fertilised egg does not develop until the young leaves the pouch. This is known as delayed implantation. At any one time a female kangaroo may have a joey (young kangaroo) being weaned, a young one being suckled in the pouch and an embryo in the uterus awaiting development. o Kangaroos have the amazing ability to produce two kinds of milk at the same time. The milk produced by the teat for the developing young in the pouch contains much less fat than the milk produced by the teat being used by the joey outside the pouch. o When environmental conditions are not good, such as in times of drought, young joeys do not survive and any fertilised egg does not implant. Females do not begin reproducing again until conditions improve. describe and explain the short-term and long-term consequences on the ecosystem of species competing for resources o Competition in ecosystems is the struggle between organisms for the same resource o Competition can be between members of the same species or between members of different species. o In the short-term, competition reduces the chance of survival and restricts the abundance of all competitors o In the long-term, one of the competitors will eventually be more successful and drive out or significantly reduce the numbers of other competitors o A particular ecosystem can support only a certain number of each type of species. o Competition may be between members of the same species, or between members of different species. o Each year many more offspring are produced by most organisms than can survive. While some young will be consumed as food by other organisms, many die in the competition for limited resources. 14 identify the impact of humans in the ecosystem studied o Humans can bring about rapid alterations and widespread change. Our effect is often destructive to the original environment and its other inhabitants. o Industrialisation and urbanisation can drastically change the natural environment o For example in our local area o industrialisation and urbanisation has drastically changed the natural environment o Sedimentation of the river occurs. o Dredging the bay for land reclamation has also been done by humans. Read Tweed Coast PoM document which outlines some impact and concern. Some information from page 30 has been highlighted which indicates human impact. Document is available on website. Answer the question: Is human impact always negative? 15