In order to understand about life, we must think hard about how life interacts with the physical aspects of the earth (abiotic). The most important abiotic aspect is the weather, or in regional terms, the climate. The nature of soil is dependent on the climate. And the nature of the plants is dependent on the soil and climate. This leads inevitably to the nature of the animals that are bound directly or indirectly to the plant life. Thus, climate, soil, plants and animals are inextricably bound to each other, interacting in many ways at various degrees of dependency.
It is useful therefore to start from a macro viewpoint and work our way to the micro, rather than the usual habit of text books which start at the micro and get more and more macro.
I think in an introductory course it is best to start with those aspects of biology that are commonly known to all people, and to specialise later in the course as knowledge increases.
A biome is the broadest justifiable subdivision of the plant and animal world - an assemblage and association of plants and animals that forms a regional ecological unit of sub-continental dimensions. A biome is actually an interacting set of ecosystems that extends over a large are of the earth, and its establishment and maintenance depends not only on climate and soils, but also plants and animals - from the tiniest bacteria to the largest of mammals.
The distribution of biomes results from 2 major factors - climate and terrain (or geography).
The key climatic factors are 1. the atmosphere and its circulation systems, which determine where moisture-carrying air masses do and do not go; and 2. the energy source of those circulatory systems - the sun. The sun's energy drives atmospheric movements, sustains photosynthesis, and propels the seasons.
The main geographic factors are 1. the distribution of the land masses and ocean basins; and 2. the topography of the continents.
Plant biomes are based primarily on the distribution of the dominant vegetation.
Animal biomes are usually named after regions because their distribution is more difficult to define.
A biome's boundaries are determined by climate more than any other factor. Eg tundra is colder and has a shorter growing season than other biomes, it has fewer kinds of vegetation. Towards the equator, precipitation becomes increasingly important, producing temperate communities of desert, grassland and forest in increasing order of precipitation. In the tropical and subtropical biomes which occur in the equatorial latitudes there is a relatively smaller range of temperature during the year, and their variation is also determined by the amount of precipitation. Thus there are not only tropical forests but also tropical grasslands and tropical deserts. In addition, seasonal distribution is important. Some areas could be tropical forest but that all their rain comes in just two months rather than evenly distributed
Another important factor is altitude. Changes in vegetation with increasing altitude resemble changes in vegetation due to increasing latitude. It isn't entirely the same. For example, increasing altitude means increasing UV. And increasing latitude usually means different amounts of light because of changing daylength, this doesn't happen in changing altitude.
Biomes are not just on land, and aquatic biomes will be mentioned later.
Click here for tundra Figure
Click here for another tundra Figure
is the northern most biome. Places wherever the snow melts seasonally (there is no Southern Hemisphere equivalent because there is no land above water in the proper latitudes.
Long harsh winters, very short summers.
Little precipitation (10-25cm per year) most of it in summer.
Tundra soils are geologically young, formed in the last ice age.
Soils are nutrient poor, little organic litter.
Permafrost. Surface melts in the summer. Permafrost prevents large plants from growing.
Landscape is thus flat, swampy, shallow lakes, bogs.
Species are few but often in great numbers.
Dominated by mosses. lichens, grasses, sedges, annuals.
Year round are: Weasels, Arctic foxes, snowshoe hares, snowy owls, hawks.
Summer visitors: musk-oxen, caribou.
No reptiles or amphibians
Insects: mosquitoes, flies are in great numbers after surviving the winter as eggs or pupae.
Tundra is very slow to regenerate
Taiga (northern boreal forest)
Click here for taiga Figure
Click here for another taiga Figure
Dominated by conifers.
just south of the tundra, stretches across N America and Eurasia. 11% of the land surface.
No equivalent in the Southern Hemisphere.
Winters cold and severe
Growing season a little longer than in tundra
precipitation is small (~ 50 cm per year)
acidic soil, mineral-poor, deep layer of pine and spruce needles at surface
permafrost is very deep or absent
numerous ponds and lakes created by last ice age ice sheets
Vegetation: dominated by spruce, fir and other conifers
deciduous trees - aspen, birch occur
conifers are drought resistant (needle leaves)
drought is in the winter when plant roots cannot absorb water, which is frozen
large animals: caribou (migrate to taiga i winter from tundra) wolves, bears, moose
small animals: rodents, rabbits, furry animals such as lynx, sable mink
birds: in summer
insects abundant
amphibians and reptiles few except southern parts.
Temperate forest areas of relatively high precipitation
temperate rain forest
Click here for Temperate Rainforest Figure
200-380 cm precipitation
eg nw coast of N America, se Australia, south S. America
rainfalls as moist airs is lifted up by mountains
temp rainforest usual close to the coast
maritime influence means narrow temp fluctuation - mild winters, cool summers.
dominated by evergreens such as western Hemlock, Douglas fir, Sitka spruce
rich in epiphytes - mosses, club mosses, lichens, ferns
animals: squirrels, deer, many birds.
presumably amphibians and reptiles
complex ecosystem easily disturbed and easily permanently damaged.
temperate deciduous forest
Click here for temperate deciduous forest Figure
75-125 cm precipitation per year
hot summers, cold winters.
rich soil overlying clay
in ne and mid-east US dominated by broad-leaved hardwood such as oak, hickory , beech
in southern areas of this biome broad-leaved evergreens occur.
large animals: puma, wolves, deer, bison, bears
many small mammals and birds
abundant amphibians and reptiles
much original forest has been logged, and regenerated forest is semi-natural
many areas deforested and used for agriculture
much soil depletion and erosion
Temperate grasslands
Click here for prairie Figure
moderate precipitation 25-75 cm
soil very high organic content
eg prairie, steppe
many kinds of grasses, up to 3 m high before man in N America
good for grazing, thus bison.
wolves, coyotes in drier areas. Kangaroos in Oz
prairie dogs, foxes, ferrets, birds of prey, grouse reptiles (eg snakes) lots of insects
this land very suited to agriculture, so little natural remains excepts some parts of east Eurasia
eg Ukraine, American mid-west
Chaparral
Click here for chaparral Figure
up to 150 cm precipitation, mostly in winter
mild winter, hot dry summer. Mediterranean climate. (Med, California, WA, Some of Chile, S Africa)
soil thin and infertile
frequent fires - vegetation is adapted to fire
many plants can grow again even if burnt to the ground - underground large root stock - lignotuber
problems if fires are not allowed to burn
dominated by dense growth of evergreen shrubs - drought resistant pine, oak
In Australia - various eucalypt species - called sclerophyll forest after leathery drought resistant leaves
Lush growth in rain season, dormant in hot season
small animals such as deer, chipmunks, kangaroos in Oz.
many reptiles such as lizards
Desert
Click here for desert Figure
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less than 25 cm precipitation
found in both temperate and tropical regions
low water content of air leads to temperature extremes daily
some deserts have so little rain that they are virtually devoid of plant life
(eg Namib desert, Atacam-Sechura desert of Chile and Peru)
soil thus has low organic material and high mineral content
plant cover is sparse and soil mostly exposed
Both perennials and annual plants (after rain)
plants adapted to extremes to conserve water and survive drought
plants adapted to prevention of grazing (each spines)
and can secrete substances to prevent other plants growing nearby
desert animals are small, often night foragers
many desert adapted insects
reptiles - snakes lizards, tortoises
mammals - rodents, kangaroos
birds of prey
Savannah (savanna)
Click here for savannah Figure
Click here for another savannah Figure
85-105 cm precipitation
tropical grassland with widely scattered clumps of low trees
yearly temp range is small, so seasons regulated by precipitation (as in temperate grasslands)
soil low in essential minerals, often rich in aluminium (red soils of Oz, bauxite in WA)
best known in Africa, but also in north Australia and in S. America continent
wide stretches of grasses interrupted by trees such as acacia (thorny for herbivore protection)
fire adapted vegetation
African savannah is amazing - the largest assemblage of hoofed animals in the world
great herds of wildebeest, antelope, giraffe, zebra
large predators such as lions hyenas
migratory herds
many parts of savanna used for grazing, overuse has caused desertification.
Tropical rainforests
Click here for tropical rainforest Figure
Click here for Surinam Figure
Click here for snake Figure
temperatures always high, daily rainfall
200-450 cm precipitation
much of the rain is from locally re-cycled water from tree transpiration
often in areas where the local soil is highly leached by high rainfall - poor in nutrients and organic material
high temp means rapid decomposition, the nutrients are quickly absorbed by the plant growth
thus most of the mineral nutrients are locked in the vegetation, not the soil
so when a tropical forest is chopped down or burnt, it cannot recover.
very productive (captures a lot of light energy from photosynthesis)
very high in species diversity and variation
no single species dominates
vegetation sparse on the understorey floor except near rivers or re-growth areas
very high humidity beneath the overhead canopy
three distinct storeys of vegetation
at the top are the crowns of the tallest trees, exposed to direct sunlight
the middle storey is a continuous canopy of leaves that lets in little sunlight
understorey is small plants specialised for low light levels, and seedling of taller trees.
trees usually evergreen flowering plants (angiosperms)
shallow roots forming a mat of about 1 metre on the surface
extensive communities of epiphytes, many climbing plants
animals are extremely abundant - insects, reptiles, amphibians, mammals, birds
most mammals live in trees, such as monkeys and sloths
some ground dwellers, such as elephants, tigers, pigs
human populations used to live in balance, but new invaders causing extensive destruction
hope to talk more about this when discussing problems in biology
Rivers and streams are flowing water ecosystems
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wetlands are transitional between aquatic and terrestrial ecosystems
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Click here for littoral zone Figure
Highly productive zone ie the most photosynthesis, in part because it receive nutrients form the land
animals include amphibians, crustaceans, worms reptiles such as turtles, fish, insects.
limnetic zone is open water and as deep as sunlight penetrates.
main organisms are plankton, large fish
profundal zone
beneath the limnetic zone
lack of light precluded vegetation.
area of decomposition
thus mineral rich and anaerobic
fewer forms of life.
Thermal stratification and turnover
Click here for water circulation Figure
the layering due to light penetration ability is also enhanced by thermal stratification - vertical layering by temperature
This is because water warmed by sunlight is less dense (rises)
so cool water remains at the bottom of the lake
there is an abrupt temp transition called the thermocline
In temperate lakes, falling temperatures in Autumn causes a mixing of the water
the surface water cools and descends, mixing with the bottom water
the water rises and descends, mixing everything to an even temperature
the same things happens in spring when ice melts and cold water descends to push up the bottom water (4C)
This mixing brings essential minerals and nutrients to the surface for use by organisms
In the tropics, this doesn't occur because the temp changes very little
Click here for marine zones Figure
oceans are deep
oceans profoundly influenced by tide and currents,
coastal areas can be influenced by big currents, eg Gulf Stream to UK and Norway
intertidal zone - shoreline separating low and high tides
high levels of nutrients, abundance of oxygen, so biologically productive
but action of water makes environment changeable, even on a daily basis
most sand dwellers are thus burrowers (no anchorage sites)
rocky shores provide anchorage for eg mussels, barnacles, intertidal algae are all adapted to anchor and to survive mechanical damage from wave action
the neritic province
is open ocean from the shoreline to a depth of 200 metres
nekton such as sharks, tuna, porpoises; larger benthic organisms such corals, spiny lobsters, starfish, are confined to shallow neritic waters (less than 60 metres deep) because that is where the food is (food is plankton, algae, etc)
upper reaches of neritic province called euphotic region, where light penetrates sufficiently to provide for photosynthesis (to about 100 metres)
oceanic province
open ocean deeper than 200 m
it is most of the ocean
88% of the ocean is deeper than 1,500 m
there are few organisms at depths past the penetration of light
principal exceptions being organisms found at thermal vents
animals of the abyss rely on food that drifts down from above
All terrestrial and aquatic life interact with one another
The various biomes and aquatic zones have been discussed separately, but of course they do not exist in isolation.
for example:
* when parts of the Amazon basin flood, many fish leave the river bed and range the forest floor, where they play a role in seed dispersal.
* in the Antarctic the waters are more productive than the land, but birds and other animals that rest on the shoreline provide nutrients from their waste products (feathers, excrement, etc) that support insects, fungus, lichens on the land. These animals thus provide a link between the two environments.
* inhabitants of different life zones may interact over very long distances - eg migratory birds and fish.
eg tuna migrate across the pacific ocean; flycatchers spend summer in N America and winter in central and South America. Many migratory animals spend critical parts of their life cycles in different land areas (and therefore different political boundaries), thus making their conservation difficult (how can you save a rare bird by conservation in your country if everyone in the next country shoots them?!!) Such phenomena makes it difficult for people to understand ecological concepts and certainly makes it difficult to apply them.
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