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Introduction
• The biosphere is the biologically inhabited portion of the Earth in which ecosystems operate
• Studies of the biosphere are linked with geology, ecology, soils, atmospheric processes and climate, oceans
• Humans influence the biosphere through a range of deliberate and inadvertent practices
• Biomes are major global scale zones with characteristic life forms of plants and animals
Functions and processes within the biosphere: characteristics
• The biosphere is characterized by its dynamism
• Boundaries within the biosphere result from a range of factors– Often along environmental gradients– Often not a sudden change but transitional areas
(ecotones)
• Each region of the biosphere has distinctive energy flows, biomass, trophic levels, nutrient cycling
Functions and processes within the biosphere: controlling factors
• Temperature regime– Actual temperature and seasonal pattern is critical for life– Growing season creates a base-line of food for others– Adaptability to temperature ranges
• Moisture availability– Local rainfall regime – esp. length of dry season– Potential evapotranspiration and accessibility to river/groundwater
• Zonal factors– Regional macroclimate (equatorial, monsoonal etc) correlate to biomes– Creates favourable/unfavourable conditions for life
• Azonal factors – Disrupt otherwise climatically-controlled pattern– Geomorphology affects drainage and aspect.– Geology
Functions and processes controlling the biosphere: The major biogeographic realms
• Biogeographical realms are divided into zones/biomes
• Classification of realms– Holarctic (from Laurasia) – Palaearictic (Eurasia) and Nearctic (N
America Greenland)
– Palaeotropic (from Gondwanaland) – southern continents; Afrotropical, Indian, Indomalaysian , Neotropical, Australia, Antarctic realms
– Usually ignores the oceanic realms
– Classification helps in taxonomy
• Past climatic and tectonic changes are vital to today’s patterns
• Climate– mean annual temp ~25o with little seasonal variation
– 2000mm rainfall/yr – dry season no longer than 5 months
– Further from equator = increased seasonality
• Soils– high rates of biogeochemical activity
– Infertile soils, lack of recently weathered rock – oxisols
– Fertility is dependent on continual leaf litter
– Soil type changes with variability in seasonality
• High net primary productivity – 40% global terrestrial productivity
– Degree of seasonality has a large impact on primary productivit
Equatorial and tropical forests
…cont• Rainforest vegetation
– Broad leaved evergreens dominate in a closed canopy
– Competition for light causes stratification of canopies and epiphytes and lianas (adaptive)
– Distinctive tree types within each stratum
– Adaptations for light, surplus water removal , phanerophytes
– Characteristics between realms remain similar but actual species vary - e.g. dipterocarps (Indian) vs legumes (S American)
• Rainforest animals– Animal species often restrict their range to a single stratum
– Animal adaptations (prehensile tails, fruit eating birds)
– Lack of under-storey vegetation allows space for large ground dwelling animals – wind pigs, jaguars, large rodents
…cont• Regeneration
– When natural clearings appear due to fire, wind or water species compete for the new niche (especially light)
– Soil erosion and nutrient loss at a minimal
– Mimicked by humans in shifting cultivation
• Complexity– Associations of vegetation rather than domination by single species
– High species diversity probably due to complex structure, length of time since major climatic disturbance
– Local specific azonal factors cause high diversity – e.g. slope, local geology, drainage
– Historical shifts between savanna and forest
Savanna• Climate
– Temperature is similar to rainforest but a longer dry season
– Dr season = >250mm/month for > 5 months
• Gradient from the equator– Savanna woodland → tree savanna → shrub savanna → savanna
grassland
• Soil = one of the major controls– Most found on continental shields – ancient infertile soil
• Ecosystem change– Easily influenced by human activities and major climatic readjustment e.g.
Quaternary
…cont• Vegetation
– More open canopy than forests: few trees except near water table
– Mosaic – diversity of structure due to differences in water and soil nutrients availability
– ‘Fire season’ – allows fruiting and nutrient supply
– Xeromorphic adaptations and Rhizomes
– Grassland stands dominated by few species
• Animals– Large numbers of herbivores (esp. Central and East Africa)
– Large animal predators occupy wooded areas of shelter, preying on herbivores
– Adaptations – nocturnalism to reduce water loss and migration to track seasonally available food
Deserts• Climate = dominant control (hot and dry all yr)
– Insufficient moisture for complete ground cover
– Large diurnal temp fluctuations
– Some areas = regular but insufficient rain to counteract evaporation
– Some areas = no sporadic rainfall for years
• Soils– Poorly developed but increased nutrients around roots
• Basic ecology– Vegetation = varied but low in height and very open stands
– Clustering dependent on water, local geology, geomorphology
– Biomass is mainly underground – geophytes or therophytes
– Low biodiversity
– Net primary productivity is strongly related to rainfall
…cont• Adaptations
– Plant and animal adaptations to control evaporation and maximise water conservation (xeromorphic)
• Plants adaptations– Control transpiration (nocturnal stomatal opening)
– Woodiness prevents wilting
– Lengthy dormant season
– Annual plants – dependent on rainfall season
• Animal adaptations– Physiological - surface area/body mass ratio, sweat control etc
– Behavioural – nocturnal, dormancy, cryptozoic
Summary • Themes for drawing geographical comparisons
between biomes– Climate, soil, wildlife types, adaptations– Local human factors also alter biomes
• Ecotones• Tropical biomes - forests, savanna, desert• Temperature biomes – forest, grasslands• Cold biomes – taiga, tundra