SciencePowerPoint Presentation

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