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______________________________________________________________________________ Part C: The Biosphere Unit 3: Properties of Biological Communities 1. Definition of Community The following definitions need to be known: - Ecosystem: a group of inter-dependent organisms and the environment in which they live (e.g. bees, flowers, butterflies and grass in a garden.) - Habitat: The place where an organism lives (e.g. a river, rocky shore) - Community: All the organisms living in a particular habitat (e.g. in soil (the habitat), the community consists of earthworms, fungi, plants, etc.). A community is thus a group of populations of different species living in the same place at the same time. 2. Interactions between Organisms In the natural world, no organism is an autonomous entity isolated from its surroundings. It is part of its environment, rich in living and non living elements all of which interact with each other in some fashion. Biological interactions occur since organisms in an ecosystem interact with each other. Biological interactions are the relationships between two species in an ecosystem. There are many types of relationships which are classified either on the effects or on the mechanism of the interaction. The interactions between two individuals will vary greatly in these aspects as well as in duration and strength. The interactions between two species need not be through direct contact. Due to the connected nature of ecosystems, species may affect each other through intermediaries such as shared resources or common enemies. 2.1 Competition Competition is a relationship between two individuals which would like to obtain a similar limited resource. This occurs since individuals in a species need limited environmental factor for growth such as light, food, water, mates. Therefore, since the resource is limited, these must compete with each other in order to obtain it for survival. Competition is a very important factor in evolution. As a result, several species less suited to compete for the resources may either adapt or die out. According to evolutionary theory, this competition for resources plays a critical role in natural selection. Two types of competition exist: Competition between members of the same species is known as intraspecific competition. Competition is also present between individuals of different species and is known as interspecific competition. Intraspecific competition occurs for mates, territory and food. ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 1 ______________________________________________________________________________ 2.1.2 Three Classic Studies of Interspecific Competition Scientists have classically studied three interactions 2.1.2.1 Paramecium: a laboratory "bottle" experiment Paramecium is a single-celled protozoan that feeds on bacteria. It can be raised easily in a test-tube, in a soup of bacteria, which is its food supply. What will happen if two species are raised separately, and then together? As the figure below shows, both species thrive when raised alone, reaching the carrying capacity set by the volume of the test-tube and the supply of bacteria. However, when raised together, the growth rate is slowed for both. Eventually, one species declines and the other takes over and grows to the carrying capacity of the test-tube. Evidently these two protozoans are competing for limiting resources (bacteria and space), and share the same niche. Competition has caused only one species to persist and the other to die out. Results of Paramecium bottle experiment 2.1.2.2 Warblers in a spruce forest Warblers are migratory, spending the winter in the tropics, and flying to northern forests in early spring to set up territories, mate, and rear their young. Cape May Warbler An important study was made of five species of warblers. These warblers are similar in body size, beak size, and all feed on insects. A study of the feeding behavior of these five warblers found many differences in the way they made use of the habitat. These species differed in what part of a spruce tree they frequented, whether they captured insects whilst flying, from needles, or under bark, and so on. The conclusion was that each species occupied a distinct niche. This ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 2 ______________________________________________________________________________ study therefore showed that even superficially similar species really are different, upon close inspection. 2.1.2.3 Barnacles in the inter-tidal zone: a field experimental study Barnacles occur on near-vertical rock walls in the inter-tidal zone, which means that they are submerged at some times and exposed to the air at others. A study in Scotland examined the vertical distribution of two species: Balanus, which occurs lower in this zone, and Chthamalus, which occurs higher. Barnacles filter-feed small plankton from the water, so can only feed when submerged. Observations of the two species could suggest that competition may be occurring. Through experiments it has been shown that larvae of each species settle throughout the zone of the other, but adults are not found throughout (figure below). It was established that Chthamalus could thrive in the lower zone if protected from Balanus. Otherwise, Balanus, which is a larger and more robust species, crushed neighboring Chthamalus as it grew in size. Chthamalus was excluded from the lower inter-tidal. At the upper limit, however, both species were limited by their ability to withstand desiccation. Chthamalus, the inferior competitor, was better adapted to desiccation and so occupied the higher portion of the inter-tidal zone. ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 3 ______________________________________________________________________________ 2.1.2 The Result of Competition So what happens when two species compete with each other? Can two species ever coexist? Does the same species always win out? These results have been answered through many "bottle" studies with flour beetles, Drosophila, yeast, various plants. Interspecific competition among ecologically similar species is the major factor that determines the structure of animal and plant communities. In general, when two species competing for a resource occur together and compete, these either coexist or else are subject to competitive exclusion. The main question is however, can competing species coexist or not, and what are the major factors that affect coexistence. In general, it has been shown that one species wins, and one species is eliminated. This is the competitive exclusion principle which stats that: No two species of similar requirements can long occupy the same niche (coexist). When two species competing for the same resource occur, these are normally subject to competitive exclusion. This is since one of the two competitors will always have an ever so slight advantage over the other. Therefore, the other species that leads to extinction of the second competitor in the long run or to an evolution of the inferior competitor towards a different ecological niche. As a consequence, competing related species often evolve distinguishing characteristics in areas where they both coexist, as in the case of the warblers. Competition is a powerful force of natural selection. There are many examples of closely related species that differ "just enough" to reduce niche overlap and permit coexistence. Competition likely affects species diversity. In the short run, competition should cause a reduction in the number of species living within an area, preventing very similar species from cooccurring. In the long run, however, competition is likely to increase species diversity, by acting as a force for specialization and divergence. Does the same species always win? In the case of paramecium, the same species always won. Studies with flour beetles, in contrast, found that changes in temperature and moisture could shift the outcome in favor of one or the other species. ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 4 ______________________________________________________________________________ 2.2 Predation Predation is defined as the removal of organism from a population by another organism. The animal that hunts and kills other organisms is called the predator, while the prganism which is killed is called the prey. This is a +/- relationship, in which case the predator benefits (food) and the prey is negatively affected (it is killed) Predators are either carnivores or omnivores. Carnivores consume meat, whilst omnivores, such as humans, eat both meat and plants. Herbivores can also be considered as predators since they eat plants. However, plants are eaten only in part and are left alive. Different hierarchies of predators exist for example though small birds prey on insects, they may in turn be prey for snakes, which may in turn be prey for hawks. A predator at the top of its food chain (that is, one that is preyed upon by no organism) is called an apex/ top predator; examples include the Great White Shark, tiger and crocodile and even omnivorous Humans. Many predators are specialist, that is they specialize in hunting only one species of prey. Others are more opportunistic and will kill and eat almost anything. The difference between a predator and a parasite is that for a predator kills the prey, whilst the parasite feeds on the prey whilst it is alive. Examples: Several examples are given below ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 5 ______________________________________________________________________________ 2.3 Parasitism Parasitism occurs when an organism (parasite) feeds on another (host) without killing it, yet causing some harm. Numerous examples of parasitic organisms occur in all kingdoms (Bacteria, fungi, protozoans, plants and animals) which parasitise a wide range of hosts. In contrast, a parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism which it ultimately kills (and often consumes) in the process. Thus they are similar to typical parasites except in the fate of the host. Examples are numerous species of paraitoid wasps. Various types of parasites exist. In general we distinguish two types: - Parasites that live inside the body of the host are called endoparasites (e.g., - hookworms that live in the host gut); and Parasites that live on the outside are called ectoparasites (e.g., some mites). An epiparasite is a parasite that feeds on another parasite. Many endoparasites acquire hosts by passive mechanisms, such as the nematode Ascaris lumbricoides, an endoparasite of the human intestine. A. lumbricoides produces large numbers of eggs which are passed from the host's digestive tract into the external environment, relying on other humans to inadvertently ingest them in places without good sanitation. Ectoparasites, on the other hand, often have elaborate mechanisms and strategies for finding hosts. Some aquatic leeches, for example, locate hosts by sensing movement and then confirm their identity through skin temperature and chemical cues before attaching theselves. Parasites can also be one of the following: - Obligate parasite - the parasite cannot complete its life cycle without a host; - Facultative parasite - the parasite can complete its life cycle independent of a host. - Stem parasite - the parasite attaches to the host stem. - Root parasite - the parasite attaches to the host root. - Holoparasite - plants that are completely parasitic on other plants and have virtually no - chlorophyll. Hemiparasite - plant that is at least partly photosynthetic but also usually parasitic. Hemiparasites may just obtain water and mineral nutrients from the host plant. Many obtain at least part of their organic nutrients from the host as well. Below are examples of parasitic organisms: 2.3.1. Parasitic plants - Orobanche (Broomrape): The broomrape is a holoparasitic root parasite attacking a variety of plants, including broadbeans; - Cuscuta (Dodder): a emiparasitic stem parasite attacking a large variety of plants including thyme. ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 6 ______________________________________________________________________________ 2.3.2 Intestinal parasites: The are parasites that populate the gastro-intestinal tract (These are not endoparasites!). In humans, they are often spread by poor hygiene related to feces, contact with animals, or poorly cooked food containing parasites. -Taenia (Tape worm) Taenia is a genus of tapeworm that includes some important parasites of livestock and humans. All members of this genus have an "armed" scolex, meaning that there are hooks on the "head" region, used to grab onto the walls of the intestine. The lifecycle of of the Tapeworm is given below. Head (scolex) of Taenia 2.3.3 Endoparasites Various examples are present, most of which give rise to serious diseases. A few examples are: - Giardia lamblia (the most common intestinal protozoan in the United States): causes Giardiases; - Trypanosoma: protist causing sleeping sickness; - Leishmania: protist causing Leishmaniasis; - Plasmodium: protist causing malaria. This has two hosts that is mosquitos and humans. Therefore it has a very complex life cycle which is described in the diagram below: ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 7 ______________________________________________________________________________ - Liver flukes: very complex lifecycle involving two hosts. Two examples are given below: The Chinese liver fluke The Sheep Liver FLuke ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 8 ______________________________________________________________________________ 2.3.4. Ectoparasites Examples include the following - Acarina (Ticks, some mites); - Tsetse Flies; and - some leeches. 2.4 Symbiosis Symbiosis means living together. It therefore describes obligatory relationships which may be beneficial or harmful top one or both organisms. Symbiosis can be divided into commensalism, amensalism and mutualism. 2.4.1 Commensalism A symbiotic interaction between two living organisms, where one organism benefits and the other is neither harmed nor helped. The term commensalism derives from the Latin com mensa, meaning sharing a table. Examples are: - Phoresy: Using a second organism for transportation. Examples are the remora on a shark, or mites on dung bugs. Both temporary and permanent phoresy exist; and - Inquilinism: Using a second organism for housing. Examples are epiphytic plants (such as many orchids) which grow on trees, or birds that live in holes in trees. 2.4.2 Amensalism A symbiotic interaction between two species in which one impedes or restricts the success of the other without being affected positively or negatively, by the presence of the other. Usually this occurs when one organism produces a chemical compound that is detrimental to another organism. For example, the bread mold Penicillium secretes penicillin, which is a chemical that kills bacteria. A second example is the black walnut tree and eucalyptus. Their roots secrete a chemical that harms or kills some species of neighboring plants. 2.4.3 Mutualism An interaction between two or more species where both species derive benefit. Mutualisms can be lifelong interactions involving close physical contact They can also be briefer such as those between flowering plants and pollinators. Several examples are given below: 2.4.3.1 Lichens Lichens are in fact a symbiotic lifeform between a fungus and a alga. This symbiosis is so intense that seemingly a new lifeform generates: the lichen. This has a very specific structure shown in the diagram below. In brief a network (mycelium) of fungal hyphae host blue green algae within the network. The advantage is such that these symbionts are capable of living in conditions much harsher than the components making up the lichen would. In fact, they tolerate numerous dry habitats and may colonize bare stone. Lichens often are the first to settle in places lacking soil, ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 9 ______________________________________________________________________________ constituting the sole vegetation in some extreme environments such as those found at high mountain elevations and at high latitudes. Some survive in the tough conditions of deserts, and others on frozen soil of the arctic regions. In the relationship, the fungus gives the algae protection whilst the algae gives nutrients to the fungus, which nutrients it harvests from photosynthesis. 2.4.3.2 Nitrogen Fixation Legumes such as clover, beans, alfalfa and peanuts, contain symbiotic bacteria called rhizobia within nodules in their root systems. These produce nitrogen compounds from atmospheric nitrogen and help the plant to grow and compete with other plants. 2.4.3.3 Mycorrhiza A mycorrhiza (typically seen in the plural forms mycorrhizae or mycorrhizas, Greek for fungus roots) is the result of a symbiotic association between a fungus and a plant. This symbiosis takes place at the root level, where individual hyphae extending from the mycelium of a fungus colonize the roots of a host plant. ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 10 ______________________________________________________________________________ 2.4.3.4 Ant-aphid mutualism The aphids are protected against predators by the ants who cultivate the aphids for their secretions of honeydew, a food source. 2.4.3.5 Evolutionary Importance of Mutualism Mutualism is important in evolution from a co-adaptation and a co-evolution point of view. Coevolution is a change in the genetic composition of one species (or group) in response to a genetic change in another, whilst co-adaptation is a joint adaptation to an environmental stimulus. Mutualists have co-evolved together and have a survival advantage over organisms occupying the same habitat, or else the individual organism in the association. Therefore, they are selected for, This is due to co-adaptation to harsh environments, allowing for a better survival. ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 11 ______________________________________________________________________________ 2.5 Summary of Interactions The following is a summary of the interactions described and more: Effect on X Effect on Y Type of interaction 0 0 Neutralism - 0 Amensalism + 0 Commensalism - - Synnecrosis + + Mutualism + - Predation or Parasitism Some types of relationships listed by the effect they have on each partner. '0' is no effect, '-' is detrimental, and '+' is beneficial. Neutralism is a lack of interaction. Since all species sharing an environment interact in some way, a complete lack of interaction is rarely seen in nature. However, the term can also signify a relationship in which each species derives neither benefit nor detriment to any measurable degree; and Synnecrosis is detrimental to both species. It is a rare and necessarily short-lived condition as evolution selects against it. ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 12 ______________________________________________________________________________ 3. The Ecological Niche 3.1 Definition and explanation A niche is a term describing the relational position of a species or population in an ecosystem. It is defined as the role amd relationships of an organism within its community. The niche for each species describes how a population responds to the abundance of its resources and enemies (e. g., by growing when resources are abundant, and predators, parasites and pathogens are scarce) and how it affects those same factors (e. g., by reducing the abundance of resources through consumption and contributing to the population growth of enemies by falling prey to them). The abiotic or physical environment is also part of the niche because it influences how populations affect, and are affected by, resources and enemies. The description of a niche also includes descriptions of the organism's life history, habitat, and place in the food chain. A niche can be depicted as a graph of productivity vs environmental characteristics as given below. This can be in one or two dimensions. On the, a niche is often shown as a hypervolume graph, that is a graph with several facets, as given below: ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 13 ______________________________________________________________________________ A generalist species would have a wide niche breadth. However a specialist species would have a niche which is less wide. A specialist species may have resulted from restriction of the niche of a generalist species. 3.2 Fundamental and realized niche The full range of environmental conditions (biological and physical) under which an organism can exist describes its fundamental niche. However, due to pressure from, and interactions with, other organisms (e.g. superior competitors) species are usually forced to occupy a niche that is smaller narrower than the fundamental niche. Organisms will occupy the part of the niche to which they are mostly highly adapted. This is termed the realized niche. Different species can hold similar niches in different locations and the same species may occupy different niches in different locations. The Australian grasslands species, though different from those of the Great Plains grasslands, occupy the same niche. Once a niche is left vacant, other organisms can fill into that position. For example, the niche that was left vacant by the extinction of the tarpan has been filled by other animals (in particular a small horse breed, the konik). When plants and animals are introduced into a new environment, they can occupy the new niches or niches of native organisms, outcompete the indigenous species, and become a serious pest. ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 14 ______________________________________________________________________________ 3.3 Competition and niche breadth According to the competitive exclusion principle, no two species can occupy the same niche in the same environment for a long time. If they do occupy the same niche, or else the hypervolume overlaps, intraspecific competition for a resource occurs. The result would be competitive exclusion, that is one species is selected against and dies, as occurred in the example of Paramecium. Alternatively, as seen further above in the example of the warblers, if two or more species have an identical niche, these must change in order to coexist. Therefore, an evolutionary change in the niche occurs, as depicted in the diagram below Interspecific competition thus narrows the niche when coexistence occurs. Alternatively, if competitive exclusion occurs and one species dies out, the species that is selected for can also occupy the niche of the species that died out. ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 15 ______________________________________________________________________________ 4. Ecological Succession 4.1 Basic Concepts Within any community some species may become less abundant over some time interval, or they may even vanish from the ecosystem altogether. Similarly, over some time interval, other species within the community may become more abundant, or new species may even invade into the community from adjacent ecosystems. This observed change over time in what is living in a particular ecosystem is ecological succession. This is the predictable and orderly changes in the composition (species occurring) or physical structure of a community over time. This occurs in all ecosystems and may be initiated either by formation of new, unoccupied habitat (e.g., a new island through lava flow or a severe landslide) or by some form of disturbance (e.g. fire, severe windthrow, logging) of an existing community. Succession occurs from an initial pioneer community (dominated by pioneer species such as lichens and mosses), through a series of different communities (called seres) until a climax community is formed where composition changes no longer occur with time. The climax community is the highest community to form for the particular place for example a woodland community. It is often seen as the end of succession since it is the most advanced community which a set of conditions can hold. The concept of a climax community assumes that the plants colonizing and establishing themselves in a given region can achieve stable equilibrium. 4.2 Forms of succession Two types of succession occur: - Primary succession: This succession occurs naturally from a new habitat for example - bare rock of a new island, from sand on a beach and from water. Secondary succession: Occurs after a particular habitat has been disturbed. For example, grassland created by logging, abandoned fields and other habitats created by man. Secondary succession is usually much quicker than primary succession since there is already an existing seed bank of suitable plants in the soil and the soil is rather fertile and deep. 4.3 Secondary succession Secondary succession occurs when for example an abandoned field develops into an Oak Forest. This occurs as given below: The first stage of succession was characterized by the pioneering colonization of annual plant species on bare ground and nutrient poor soils of the abandoned field. These annual species had short lifespans (one growing season), rapid maturity, and produce numerous small easily dispersed seeds. The annuals were then quickly replaced in dominance in the next year by biennial plants and grasses. After about 3 to 4 years, the biennial and grass species gave way to perennial herbs and shrubs. These plants live for many years and have the ability to reproduce several times over their lifespans. ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 16 ______________________________________________________________________________ After about 5 to 15 years, the sites were then colonized by a number of different softwood tree species including loblolly pines (Pinus sp.). As the softwoods increased in their numbers and grew in height, they began forming a forest canopy. This canopy reduces the amount of light reaching the forest floor. The resulting shaded under storey conditions caused the exclusion of many light loving perennial herb and shrub species. Low light conditions also inhibited the germination of pine seedlings. Perennial herb and shrub species that were adapted to low light conditions now began to take over the ground cover. The canopy also changed the microclimate of habitat near ground level. It was now more humid, has moderated temperatures, and less wind. These conditions, plus the development of a soil litter layer, allowed for the germination of hardwood species, like oak (Quercus spp.) and various species of hickory (Carya spp). The seedlings of these tree species also tolerate low light levels. By about 50 to 75 years after the initial colonization of the pioneer species, the hardwoods started to replace the softwood species in the developing forest. At this stage in the succession, the pines had maximum heights of about 25 meters, while the oaks and hickories were on average about 10 meters tall. Because of their shorter lifespans (50 years), many of the softwood species were beginning to die out and the gap that was created was then filled by a subdominant hardwood tree. Hardwood species, like oak and hickory, can live for more than 100 years. Sites more than 100 years old were found to be dominated by mature oak forests. 4.4 Mechanism of Primary Ecological succession Two examples are given below: - Succession from an aquatic to a terrestrial habitat: This is a hydrosere that is a succession which starts in water. A wetland, which is a transitional area between open freshwater and dry land, provides a good example of this and is an excellent place to see several stages of a hydrosere at the same time. ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 17 ______________________________________________________________________________ In time, an area of open freshwater such as a lake, will naturally dry out, ultimately becoming woodland. During this process, a range of different habitats such as swamp and marsh will succeed each other. This succession from open water to climax woodland is likely to take at least two hundred years (probably much longer). Some intermediate stages occur. 1st sere: Open water: Deep freshwater will not support rooted, submerged plants because there is not enough light for photosynthesis in the depths. There will be micro-organisms and plankton floating in the water. 2nd sere: Sumerged plants: Over time, sediments will be transported into the lake (or pond) by streams or rainwater draining into it from the land. Large amounts of sediment can be deposited in this way. The water depth will gradually decrease, allowing rooted, submerged plants, such as starwort and pondweed to grow. Waterlilies, which are rooted, but with floating leaves may also become established. 3rd sere: Marshland: By this stage, the water may be too shallow to support fully submerged plants. Instead, emergent plants,such as Yellow Iris, reed and reedmace, grow partly in and partly out of the water. The form a type of community called the marshland. 4th sere: Willow and Alder forest: The soil is still wet, but no longer completely waterlogged. Thereforem willows start growing and dominatee the ground. Willows will support a diverse range of invertebrates (more than 450 different species). This means that there is plenty of food for insectivorous birds. Climax Oak Forest: The soil is deep and tree species present include Oak, Ash and Beech. They are slow-growing, but because they are also tall and long-lived, in time, they will come to dominate an area. Succession from bare rock to a hardwood forest: ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 18 ______________________________________________________________________________ Rocks are colonized by lichens and mosses at first. These form the pioneer community which is the first sere. During this phase soil is deep and lacks nutrients. However, lichens create soil by dissolving rocks and mosses trap sediments, thus initiating soil formation. Eventually when the soil gets deep enough, the pioneer community is replaced by the second sere that of the grassland. This is made up of herbaceous species such as grasses and legumes which are ruderal (r) species. Ruderals grow rapidly and a high turnover occurs. The soil is still shallow and lacks nutrients. However, legumes have a symbiotic relationship with bacteria that perform nitrogen fixation. Therefore, soil nitrogen is increased. In addition, when these plants die they form part of soil humus. Therefore soil richness and depth increases. The third sere eventually replaces the grassland. This would be made up of small bushes which have deeper roots and contribute more to soil fertility and depth. The fourth and fifth sere are eventually formed both of which are forests. However, the fifth is made up of larger trees. This is the climax community which is made up of equilibrium (K) species. The climax community is stable and will remain in place as long as the present conditions are present. 4.5 Causes of Succession Succesion can be of two types. Autogenic succession occurs through a natural process of change from one community to another until the climax for a particular habitat and conditions is reached. The stimulus for change is an internal one. For example gradual soil improvement could allow a new species to develop. Conversely, an autogenic succession occurs due to an external change affecting the community. For example a sudden flood of an area could bring about a change in species, and from one succesional series, the community jumps onto another. The ultimater aim would be to reach the climax community permitted under such conditions. 4.6 Disturbance of succession Succession is a relatively delicate procedure which needs stable habitat conditions in order to reach a climax. Disturbance, which is defined as a temporary change in environmental conditions is known to affect succession. These may be natural or anthropogenic for example fire, grazing, flood, landslide, drought If conditions change temporarily due to disturbance a pronounced change in ecosystem structure that lasts longer than the change in the environment will occur. Ecosystem changes include a reversion of succession to a previous sere due to altered populations or behaviour of difference species as they respond to the stressful conditions imposed by the disturbance. ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 19 ______________________________________________________________________________ 4.7 Succession in the Maltese Islands Succession in the Maltese Islands is quite interesting, and is typical of a Mediterranean habitat. In the Maltese Islands the following succession occurred and is still occurring: Bare rock Steppe Karst landscape Garrigue Maquis Woodland ________________________________________________________________________________________________________ J. Henwood The Biosphere- Biological Communities 20