Biodiversity Past Paper PDF

BIODIVERSITY WHAT IS BIODIVERSITY?  Hens & Boon (2003) stated that biodiversity is a contraction of “biological diversity” and refers to the number, variety and variability of living organisms.  It embraces two different concepts: one is a measure of how many different living things th...

BIODIVERSITY WHAT IS BIODIVERSITY?  Hens & Boon (2003) stated that biodiversity is a contraction of “biological diversity” and refers to the number, variety and variability of living organisms.  It embraces two different concepts: one is a measure of how many different living things there are and the other is the measure of how different they are. WHAT IS BIODIVERSITY  Convention on Biological Diversity (1992) defines biodiversity as the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems”  It therefore refers to the variety of all life on earth, and explicitly recognises how the interaction of the different components of ecosystems results in the provision of essential ecosystem services on the one hand, and social and recreational opportunities on the other, including being a source of inspiration and cultural identity WHAT IS BIODIVERSITY  Biodiversity takes into account the diversity of species (a population or group of populations whose members have the potential to interbreed and produce fertile offspring), , their genes, their populations (group of similar organisms in the same area), and their communities (groups of populations).  There is growing evidence that biodiversity has a vital role in attaining the Millennium Development Goals: It contributes to poverty reduction and to sustaining human livelihoods and well- being through, for example, underpinning food security and human health, providing clean air and water, and supporting economic development (UNEP 2007; MA 2005a)  Biodiversity encompasses several levels of life’s organization:  Species diversity (Interspecific): Expressed in terms of the number or variety of species in the world or in a particular region.  Genetic diversity (Intraspecific): Encompasses the differences in DNA composition among individuals within a given species.  This means that it focuses on variation of the set of genes carried by different organisms  Ecosystem diversity: Community diversity, habitat diversity, and landscape diversity are all ways to view biodiversity. E.g. bio- geographic zones, biomes, eco-regions, and oceanic realms BENEFITS OF BIODIVERSITY  Biodiversity provides ecosystem services free of charge.  Biodiversity helps maintain ecosystem function.  Biodiversity enhances food security.  Biodiversity provides traditional medicines and high-tech pharmaceutical products.  Biodiversity provides economic benefits through tourism and recreation.  People value and seek out connections with nature = biophilia, “the connections that human beings subconsciously seek with the rest of life.”  Question to be answered: Do we have an ethical responsibility to prevent species extinction? CONTROLS OF SPP DIVERSITY HABITAT DIVERSITY  In some regions spp diversity is positively correlated with habitat diversity (habitat heterogeneity)  This means that habitat diversity correlates positively with greater resource gradient length and greater available niche space.  Habitat diversity is a function of differences in the physical or biological environment.  E.g. Areas with complex topography gives rise to a number habitats and wider variability of habitat types than areas with flat topography  Topography influences habitat diversity at both small and large scales  At a small scale, a field with gently rolling topography might include relatively dry hilltop soils, mesic hillslope soils, and moist soils in low-lying areas.  This means that different habitats will host different organisms that require dry and wet conditions.  Such undulating landscapes with different habitats will have greater spp diversity than a flat surface characterised by a homogenous habitat (mesic soils conditions)  At a large scale, mountainous regions can have a variety of environments extending from hot and dry low-elevation deserts, cooler and moister mid elevation regions that support woodlands and forests, and cold high-elevation tundra.  Diverse topography of mountains can often lead to reproductive isolation of spp populations and produce increased rates of allopatric speciation.  Different mountain environments support different vegetation formations.  Vegetation structure is therefore an important biological contributor to habitat diversity.  Habitat can therefore vary horizontally and vertically.  Vertical structure of a forest will produce a variety of habitats (habitat diversity).  E.g. A highly stratified forest provides differences in plant composition and microclimate in each stratum and presents a wide range of habitats for birds, mammals, reptiles, amphibians and insects.  This means that different plant species that occupy a particular stratum will provide different food sources. LARGE LAND AREAS OF THE TROPICS  Large continuous land area of the tropical zone in Africa, S. America & Australia contributes to the development and maintenance of high species diversity.  The presence of large areas of continuous habitat in the equatorial zone, such as the Amazon rainforest, allows species to have large populations and large geographic distributions.  This means that large geographic distributions that support large population sizes lead to decreased risk of extinction.  ENVIRONMENTAL STABILITY  Stable environmental climate on a short-time scale (days, months seasons & years) promotes higher biodiversity than unstable climates.  Environs with low amount of daily, seasonal, and annual variability allow spp to become finely adapted.  Such spp will develop the most efficient form and behaviour to take advantage of available resources without requiring special mechanisms that allow them to cope with a variability in environment.  E.g Short-term and long-term variability of the higher latitudes requires spp to be more generalistic in terms of survival.  Because they are generalistic, spp therefore tend to survive due to their adaptability to a wide range of conditions. DEFINITIONS  Ecological Niche - Description of the role a species plays in a biological community, or the total set of environmental factors that determines species distribution.  Generalists - Broad niche  Specialists - Narrow niche  Fundamental Niche - Full range of resources or habitat a species could exploit if there were no competition with other species.  Realized Niche - Resources or habitat a species actually uses  Deep oceans are stable in terms of temperature and salinity concentrations.  However, such environments are characterised by lower diversity of fish and invertebrates  On the other hand, shallow-water areas are environmentally unstable but are characterised by high biodiversity of fish and invertebrates.  Saline lakes have lower diversities of aquatic organisms. DISTURBANCE  Disturbance and species diversity can be argued from the intermediate disturbance hypothesis proposed by ecologist JH Connell.  According to the hypothesis, if an ecosystem remains free of disruption and disturbance, the stable homogeneous environmental conditions will favour some spp but will lead to the extinction of other spp for which the stable habitat is not favourable.  However, disturbance will produce a heterogeneous environment that will favour spp that would not survive in a stable undisturbed environments.  If however, disturbance occurs too frequently and it is too severe, it will lead to the extinction of disturbance-sensitive spp that have long generation time or occur in low numbers and are prone to extinction. COMPETITION  Natural selection and evolution of spp in the mid-latitudes is driven by adaptation to physical stresses related to climate, such as cold or aridity.  However, evolution in the warm and moist tropics is driven by interspecific competition.  The high degree of competition in the lower latitudes leads to spp developing specialised adaptation methods that restricts their distribution in terms of habitat and resource gradients.  Such spp are therefore competitively superior within narrow ranges of environmental conditions.  E.g Narrow habitat preferences decreases direct competition with other spp. JUST A REMINDER  Interspecific - Competition between members of different species.  Intraspecific - Competition among members of the same species.  Often intense due to same space and nutritional requirements PREDATION  High numbers of predator and parasite spp, particularly in the tropics, maintain high biodiversity by keeping prey populations low and decreasing the competitive exclusion of one prey spp by another.  The reduction in competition allows for more prey spp to evolve.  This leads to the coevolution of additional specialist and generalist predators.  According DH Janzen hypothesis, tropical forests contain high numbers of different tree species which occur as isolated individuals.  No tree spp appears to be capable of effectively excluding others at a landscape scale.  The restricted distribution of tropical trees is due to concentration of seed predators that limit the distribution of seeds.  Very high concentrations of specific seed predators are common in the vicinity of their host trees.  Most seeds that are found near the parent tree are devoured and this keeps the area close to the parent tree free of its own offspring  However, seeds that are transported away from the parent tree are not devoured and have greater chance of survival.  The inability of trees to establish close to other members of the same spp keeps the populations of tree spp small and dispersed. PRODUCTIVITY  Regions with high primary productivity will have high biodiversity.  This is because the vegetation in such areas produces more energy that can support more spp at the higher trophic levels.  The availability of abundant energy allows primary consumer spp to have specialised niches in terms of food.  This means that, the greater the number of primary consumers, the greater the number of predators that can be supported by the environment.  The large number of different herbivores promotes greater diversity of plants through the coevolution of specialised herbivores, pollinators and seed dispersers. CAUSES OF BIODIVERSITY LOSS BIOLOGICAL CAUSES  Habitat loss:  Habitat loss due to human intervention has accelerated biodiversity loss  Habitat loss is due to habitat fragmentation through the construction of roads, dams settlements, canals etc.  E.g. Africa by 2005 had approximately 48,9% of undisturbed environment compared to Europe’s 15,6%.  Introduction of exotic species: Some species have been intentionally and unintentionally introduced in many parts of the world.  E.g. Foxes, rabbits and cats, which were taken to Australia aboard European ships, have decimated Australia’s indigenous wildlife.  In freshwater, the stocking of exotic fish for sport, or (rarely) for food, has caused approximately 18 extinctions of fish species in North American rivers.  Catastrophic changes in the fish biodiversity of Lake Victoria (East Africa) resulted from the introduction of Nile perch  Eucalyptus, which is indigenous in Australia, has been introduced in many tropical and subtropical regions in the world, where the tree merely behaves as a pest.  Over-harvesting  Over-harvesting through poaching causes biodiversity loss  Over-harvesting due to systematic cutting of wood for heating purposes or charcoal production also lead to biodiversity loss.  The use of medicinal plants might also contribute to biodiversity loss.  E.g Common medicinal plants of South Africa include Bitter aloe (Aloe ferox), African ginger (Siphonochilus aethiopicus), Wild rosemary (Eriocephalus africanus), Pepperbark tree (Warburgia salutaris), Pineapple flower (Eucomis autumnalis), etc.  Co-evolution problems  Species that are co-evolved with another, such as plants with specialised insect pollinators, will go extinct if one of the pair goes extinct.  E.g. Moabi (Baillonella toxisperma) used to be a common tree in West-Africa.  The fruits are eaten, cooking oil is extracted from the seeds (karite) and the bark is used for medicinal purposes.  However, the plant depends on the elephants for reproduction.  Elephants swallow and disperse the seeds.  However, the reduction of elephants in countries such as the Ivory Coast, Ghana and Benin has had an important impact on the distribution of the tree.  Homogenisation in agriculture and forestry  The use of limited number of species in industrial agriculture and forestry also lead to biological diversity reduction. MODERN BIOGEOGRAPHIC REGIONS  (1) Nearctic and Palearctic (The Holarctic),  (2) Neotropical,  (3) Ethiopian (African),  (4) Oriental and the  (5) Australian COMMON BIOGEOGRAPHICAL DISTRIBUTIONAL PATTERNS  The distributions of organisms provide important evidence regarding the ecology and evolutionary history of organisms.  Endemic and cosmopolitan distributions  Plants and animals that possess very large geographic ranges distributed over most continents are cosmopolitan.  Taxa with restricted geographic ranges are classified as endemics.  Endemics are species that are found in one biogeographic region.  Species that occur in three or four regions are classified as semicosmopolitan  Species that have a large range (>4, 400, 000 km2 range) within a biogeographic region in which they are found are classified as macro- areal.  Those with small ranges are classified as micro- areal (