Module 4.4.2: Biomes and Biodiversity of Africa and Albertine Rift

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1 Module 4.4.2: Biomes and Biodiversity of Africa and Albertine Rift Key Definitions -Biome: This is a large area with similar flora, fauna and microorganisms e.g. Tropical Rainforest, Tundra in the Arctic. Each of these large communities contains species that are adapted to its varying conditions of water, temperature and soil. -Ecoregion: These are large units of land and water that contain distinct assemblages of species, habitats and ecological processes and whose boundaries attempt to depict the original extent of natural units before major land-use change.

2 Ecoregion Ecoregion reflect broad ecological patterns occurring on the landscape. In general, each ecoregion has a distinctive composition and pattern and animal species distribution. Abiotic factors such as climate, landform, soils and hydrology are important in the development of ecosystems and thus help to define ecoregions. Within an individual ecoregion, the ecological relationships between species and their physical environment are essentially similar. OR A reccuring pattern of ecosystems associated with characteristic combinations of soil and landforms that characterize that region

3 Definitions contd. Biodiversity: Biological diversity or biodiversity is the sum of species, ecosystems and genetic diversity of the earth. It also includes biological processes, some of which may operate at scales larger than single ecosystems. There are 9 biomes across Africa and its islands, and a total of 119 terrestrial ecoregions, most of them derived from the vegetation of Africa sensu White (1983). WWF uses ecoregions as a framework to establish conservation priorities and targeted programs of conservation action across large areas of land.

4 Biomes of Africa (ranked by total coverage) Tropical and subtropical grasslands, savannas, shrublands and woodlands Desert and xeric shrublands Tropical moist forests Montane grasslands and shrublands Mediterranean forests, woodlands and scrub Flooded grasslands and savannas Tropical dry forests Mangroves Temperate conifer forests (discuss each separately)

5 Lecture 2: Main Global Patterns of Species Biodiversity " Diversity would not be interesting if the level of diversity were the same everywhere. " Diversity is influenced by many interacting factors and processes notably ecological, evolutionary, geological and biogeochemical processes.

6 Latitudinal Gradients of Species Diversity " Species diversity is lowest near the poles and increases towards the tropics. " Understanding diversity gradients is not simple as there are many factors that are correlated with gradient that could possibly affect species diversity such as temperature and precipitation variability, annual net productivity and geologic history. " Factors could be +vely or vely correlated with latitude.

7 Reverse Latitudinal Gradients " Sea Birds- Non-migratory birds that forage for fish and crustaceans. The avian group reach maximum diversity in the upper latitudes (high 1 0 and 2 0 productivity of open oceans in high latitudes. " Lichens (A symbiotic relation between fungi and algae). Lichens are most abundant where high vascular plants cannot survive. Dry or cold regions (refer to Facilitation process in succession). " Other groups of taxa having reverse latitudinal gradients include marine benthic organisms, parasitic wasps and soil nematodes.

8 Altitudinal Gradients " Species diversity decreases with increasing elevation. An increase in elevation of 100m results in a decrease of temperature by 6 0 C. This is equivalent to increase in latitude corresponding to a linear distance of km. " Other physical conditions such as seasonal variations also change along altitudinal and longitudinal gradients. " Moisture increases with increasing elevation, but highest diversity of plant species (all growth forms) were found in the intermediate to low elevations (see figure).

9 Factors Correlated with Diversity " Latitude per se, does not influence species diversity, but other factors that change with latitude e.g. sun angle; day length; seasonality; temperature means and extremes; rainfall amounts and timing; winds and storms are some of the causative factors. " Primary productivity is the basic resource that fuels life on earth. Productivity is correlated with diversity both positively and negatively.

10 Positive Correlation of Diversity and Productivity " On a global scale primary productivity of terrestrial ecosystems is +vely correlated with plant species diversity. " There is a strong +ve correlation of the species richness of major taxonomic groups (i.e. trees, birds, mammals, amphibians, and reptiles) with Potential Evapo-Transpiration (PET). PET is a quotient estimated from air temperature and solar radiation. " Productive forest ecosystems are more diverse in terms of species than the less productive deserts or grasslands. " In N. American deserts the species richness and diversity of seed eating ants and rodents is +vely correlated with precipitation.

11 Negative Correlations of Diversity and Productivity " This is also known as the paradox of enrichment since this phenomenon perplexed many ecologists in the 1960s and 70s. " A common phenomenon in aquatic systems where addition of nutrients (N & P) greatly increases productivity (EUTROPHICATION). This effect reduces algal diversity and other aquatic organisms as well, and promotes algal blooms. " Addition of fertilizer to plant communities results in sharp decrease in species diversity. The same pattern is observed along natural gradients of soil fertility.

12 Diversity and Size of the Sample Area " Species/Area Curve concept. " Large areas have more species than small areas. " Species/area curves can be used to compare the rate of increase in species number with area between different regions. " Relationship S=kA z K is a constant which is the rate at which the number of species increases with area. This is related to : nature of the area and isolation and equilibrium between immigration and extinction.

13 Explanations for Increase in Diversity with Area " It could be sampling artefact. " It results from equilibrium between extinction and immigration as described by the equilibrium theory of Island (MacArthur & Wilson, 1963; 1967). " It could be a result of environmental heterogeneity.