Ecosystems and Biomes

Ecosystems and Biomes

Two organizing principles are ecosystem and biome.

Ecosystem—the totality of interactions among organisms and the environment in the area of consideration, can be looked at various scales

Encompasses both the living and nonliving portion and how energy flows among them.

Weakness—there is an almost infinite variety in the magnitude of ecosystems that can be studied:

Range includes the whole Earth itself to a drop of water.

Biome—a large, recognizable assemblage of plants and animals in functional interaction with its environment.

Most appropriate scale for understanding world distribution patterns.

Eleven major types

Often significant and even predictable relationships exist between the biota (particularly the flora) of a biome and the associated climate and soil types.

Ecotone—the transition zone between biotic communities in which the typical species of one community intermingle or interdigitate with those of another.

Terrestrial Flora

Geographers are interested in the natural vegetation of a landscape for three reasons:

1. Plants are likely to dominate a landscape (except where terrain is rugged, climate is harsh, or humans have intervened).
2. Vegetation is a sensitive indicator of other environmental attributes.
3. Vegetation is often instrumental in human settlement and activities.

Characteristics of Plants

Most are very hardy.

Survival potential is highly dependent on:

Subsurface root system

Reproductive mechanism

• Perennial—plant that can live more than a single year despite seasonal climatic variations.
• Annual—plant that perishes during times of climatic stress but leaves behind a reservoir of seeds to germinate during the next favorable period.

Common characteristics:

Roots (to gather nutrients and moisture and to anchor plant)

Stems and branches (to support and transport nutrients)

Leaves (to collect solar energy, exchange gases, and transpire water)

Reproductive organs

Floristic Terminology

Categorization by reproduction:

• Through spores
  • • Bryophytes—spore-bearing plants such as mosses and liverworts; never dominated in history, but can be very important in some localized situations.
    • Pteridophytes—spore-bearing plants such as ferns, horsetails, and club mosses; used to dominate continental vegetation, but no more.
• Through seeds
  • Gymnosperms—seed-reproducing plants that carry their seeds in cones; also known as conifers.
  • Used to be more important in the geologic past.
  • Angiosperms—plants that have seeds encased in some sort of protective body, such as a fruit, a nut, or a seedpod.
  • Have dominated planet vegetation for past 50 million to 60 million years

Categorization by stem or trunk composition:

• Woody plant—plant that has stem composed of hard fibrous material; refers mostly to trees and shrubs.
• Herbaceous—refers to plants that have soft stems; mostly grasses, forbs, and lichens.

Categorization by leaf retention:

• Deciduous—refers to trees that experience an annual period in which all leaves die and usually fall from the tree, either because of a cold or dry season.
• Evergreen—a tree or shrub that sheds its leaves on a sporadic or successive basis, but at any given time it appears to be fully leaved.

Categorization by leaf shape:

• Broadleaf—tree that has flat and expansive leaves.
  • Majority are deciduous.
• Needleleaf—refers to trees adorned with thin slivers of tough, leathery, waxy needles rather than typical leaves.
  • Almost all are evergreen.

Environmental Adaptations

Plants have two prominent adaptation strategies to protect against environmental stress.

• Xerophytic—refers to plants structurally adapting to withstand protracted dry conditions.
  • Roots, stems, leaves, and reproductive cycle can all adapt in various ways.
  • Succulent—plant that has a fleshy stem that stores water.
• Hygrophytic—refers to plants structurally adapting to withstand protracted wet conditions.
  • Hygrophyte—plant that requires a saturated or semisaturated environment (frequent soakings with water).
    • Likely to have an extensive root system for anchoring in soft ground.
    • Usually relies on the buoyancy of water for support rather than a stem.
    • Many have weak, pliable stems and so can withstand currents.
    • Hydrophytes are often grouped in with this category.
  • Hydrophyte—a water-loving plant that is adapted to live more or less permanently immersed in water.

Global Distribution of Plant Associations

Competition is key in determining which plants grow where.

Even though all conditions (climatic, edaphic, etc.) are favorable, a plant may not take hold in one area because of competition.

Floristic pattern of Earth is impermanent.

Change can be slow and orderly, as in lake infilling.

Change can be abrupt and chaotic, as in wildfire.

Climax vegetation—a stable plant association of relatively constant composition that develops at the end of a long succession of changes.

Climax vegetation is an association in equilibrium with prevailing environmental conditions.

Should persist until an environmental disturbance/change occurs.

Seral association—various stages leading up to climax vegetation.

Spatial Associations of Plants

Geographers are usually more concerned with spatial groupings than individual plants.

Groups are based on dominant members, dominant appearance, or both.

Geographers can face significant difficulties in recognizing spatial groupings.

As one tries to identify patterns and recognize relationships, one must make generalizations.

When associations are portrayed on maps, boundaries usually represent approximations.

Human interference plays a major role.

Because of human impact, climax vegetation is now the exception rather than rule.

Maps often ignore human interference and so are actually maps of theoretical natural vegetation.

Many ways to classify plant associations.

Geographers usually place emphasis on structure and appearance of dominant plants.

Major associations include forests, woodlands, shrublands, grasslands, deserts, tundra, and wetlands.

• Forest—an assemblage of trees growing closely together so that their individual leaf canopies generally overlap.
  • Forests are likely to become climax association in any area where moisture is adequate and growing season is long.
• Woodland—tree-dominated association in which the trees are spaced more widely apart than those of forests and do not have interlacing canopies.
• Shrubland—plant association dominated by relatively short woody plants.
  • Wide latitudinal range but usually restricted to semiarid or arid areas.
• Grassland—plant association dominated by grasses and forbs.
  • Prominent types are savanna, prairie, and steppe.
  • Associated with semiarid and subhumid climates.
• Desert—actually a climate, not an association per se, but is typified by plants widely scattered on bare ground.
• Tundra—a complex mix of very low-growing plants, including grasses, forbs, dwarf shrubs, mosses, and lichens, but no trees.
  • Only in the perennially cold climates of high latitudes or high altitudes.
• Wetland—landscape characterized by shallow, standing water all or most of the year, with vegetation rising above the water level.
  • Have much more limited geographic extent than any other above associations.

Various plant associations will exist in relatively narrow zones when mountain slopes have significant elevational changes in short horizontal distances.

Vertical Zonation—the horizontal layering of different plant associations on a mountainside or hillside.

Elevation changes are a counterpart of latitude changes.

Tree-line elevation varies with latitude.

Southern and Northern hemispheres experience different elevation–latitude relationship, with the Southern Hemisphere having lower tree lines.

• Exposure to Sunlight—often a critical determinant of vegetation composition.
  • Adret slope—Sun slope; slope where Sun’s rays arrive at a relatively direct angle.
    • Relatively hot and dry, and its vegetation is sparser and smaller than that on adjacent slopes with different exposures.
    • Likely to have species composition different from adjacent slopes.
  • Ubac slope—a slope where sunlight strikes at a low angle and hence is much less effective in heating and evaporating than on the adret slope, thus producing more luxuriant vegetation of a richer diversity.
    • Difference between adret and ubac decreases with increasing latitude.
  • Valley-Bottom Location—can have vegetation composition significantly different from slopes running to it.
  • Riparian vegetation—streamside growth, particularly prominent in relatively dry regions, where stream courses may be lined with trees, although no other trees are to be found in the landscape.

Terrestrial Fauna

Animals occur over Earth in much greater variety than plants.

Animals, however, tend to be much less prominent than plants in the landscape.

They tend to be secretive and inconspicuous.

Also, environmental relationships are much less clearly evidenced by animals than plants.

Their inconspicuousness makes it more difficult to study them, and their mobility has led to greater environmental adaptability among them.

Characteristics of Animals

Variety of animal life is so great that it is difficult to find many unifying characteristics.

Two universal traits (though these aren’t always immediately recognizable):

Need to eat plants and/or other animals.

Kinds of Animals

Size and habits are not valid indicators of an animal’s significance to geographic study.

Minute and seemingly inconsequential organisms can play important roles.

Examples are carriers of disease, providers of scarce nutrients.

• Invertebrates—More than 90 percent of all animal species are invertebrates (without backbones).
  • Arthropods are the most prominent (insects, spiders, centipedes, millipedes, crustaceans).
• Vertebrates—Five groups of vertebrates (those with a backbone):
  • Fish, amphibians, reptiles, birds, and mammals.
• Most mammals are placentals, having young grow and develop in the mother’s body.
• About 135 species of mammals are marsupials, in which mothers carry young, not fully developed at birth, in pouches.
• Two species of mammals are monotremes—lay eggs.
• Echidna and duckbill platypus.

Environmental Adaptations

Three different kinds of evolutionary adaptation by animals:

• Physiological
• Behavioral
• Reproductive

Example of Animal Adaptations to Desert Life

• Faunal diversity can be astounding in desert areas where water is permanent or prolonged.
• Even in areas where open water is not available, there are pockets of localized favorable habitat that permit remnant populations to survive.
• Most animals are completely nocturnal.
• Animals are more conspicuous when it is cooler, such as at night and in winter.
• Some animals follow rains in a nomadic fashion.
• Most prominently displayed by birds.
• Some spend significant time underground.
• Some bury themselves to survive long dry spells, such as freshwater crayfish and crabs.
• Text provides detailed discussion of anatomic and physiological adaptations (pp. 295–299).
• A few species of rodents can exist from birth to death without ever taking a drink.
• They get their moisture from food.
• Some species display an ability to delay reproductive processes over long dry periods until more favorable conditions occur.
• Australian desert kangaroos can delay implantation of fertilized blastocyst so it remains in an inactive state in uterus until better weather conditions occur.
• Dromedary (one-humped) camel has developed the most remarkable series of adjustments to a desert environment.
• Anatomic adaptations include:
• Light-colored and shiny summer coat reflects hot sunlight.
• Deeply cleft upper lip allows moisture loss from nose to be recycled back into mouth.
• Nostrils are horizontal slits that keep sand and dust out.
• Eyes are set beneath shaggy brows for shade, and double eyelids protect eyes from sand.
• Broad and elastic feet for good traction and protection against the hot sand.
• Physiological adaptations include:
• Highly fluctuating body temperatures that allow them to conserve moisture through minimal perspiration.
• Little production of urine and little moisture voided in their feces.
• Can stand long periods without water and can rapidly rehydrate when drinking.
• They cannot, however, store moisture in their hump.

Competition Among Animals

Competition can be both direct and indirect.

• Indirect—rivalry for space and resources.
• Direct—antagonism of predation.

Many create social groups among own species.

Some across species, such as the communal relationship among zebras, wildebeest, and impalas in East African savannas.

Individual animals are concerned either largely or entirely with their own survival.

Some animal species are concerned with the survival of mates.

Some are concerned with the survival of young (more common as a maternal instinct, though some paternal too).

Still fewer are concerned with survival of a group.

Cooperation Among Animals

• Symbiosis—association of two dissimilar organisms in which they live together in some fashion.
• Mutualism—symbiotic relationship in which the association is mutually beneficial to both organisms.
• Commensalism—symbiotic relationship in which the association is neither beneficial nor injurious to either.
• Parasitism—symbiotic relationship in which the association benefits one but harms the other; that is, one lives on or in the other, to the detriment of the host.

Zoogeographic Regions

Animals’ distribution patterns are more complex and irregular than that of plants because of their mobility.

The broad distributions of animals nevertheless do reflect a general distribution of energy and food diversity.

Nine zoogeographic regions are generally recognized.

Represent average conditions and cannot portray some common pattern in which different groups of animals fit precisely.

• Ethiopian region
  • Has most diverse vertebrate fauna and greatest number of mammalian families.
• Oriental region
  • Similar to Ethiopian but with less diversity (save for birds and reptiles; large number of venomous snakes).
• Palearctic region
  • Poorer fauna than the previous two.
  • Probably a function of higher latitudes and more rigorous climate.
• Nearctic region
  • Faunal assemblage is relatively poor (save for reptiles being well represented).
  • Largely a transitional zone between Palearctic and Neotropical groups.
  • Great similarity to Palearctic, so that some group together into a superregion, the Holoarctic.
  • Reflects how faunal dispersal occurred via Bering land bridge in geologic past.
• Neotropical region
  • Has rich and distinctive faunal assemblage.
  • Variety of habitats and isolation from other regions.
  • Has a larger number of endemic mammal families than any other region.
  • Bird fauna is exceedingly diverse and conspicuous.
• Madagascar region
  • Dominated by a relic assemblage of unusual forms.
  • Primitive primates (lemurs).
• New Zealand region
  • Fauna dominated by birds (mostly flightless).
  • Almost no terrestrial vertebrates.
  • No mammals and only a few reptiles and amphibians.
• Pacific Islands region
  • Limited faunal assemblage.
• Australian region
  • Has the most distinctive fauna of any region.
  • Lack of variety is made up for by animals’ uniqueness.

The Major Biomes

Named for dominant vegetation but encompasses fauna as well as interrelationships with soil, climate, and topography.

Tropical Rainforest or Selva— a distinctive assemblage of tropical vegetation that is dominated by a great variety of tall, high-crowned trees.

• Probably most complex of all terrestrial ecosystems.
• Distribution closely related to climate.
• Consistent rainfall and relatively high temperatures.
• Layered structure, with the second layer being a branch canopy formed by the high trees that crest above the canopy.
• Undergrowth is relatively sparse because of the lack of light.
• Interior is region of heavy shade, high humidity, windless air, continuous warmth, aroma of mold and decomposition.
• Fauna is largely arboreal—tree dwelling.
• Canopy serves as the principal food source.

Tropical Deciduous Forest

• Not closely correlated with specific climatic types; distribution is more irregular and fragmented.
• Compared to rainforest, canopy is less dense, trees are shorter, and there is less diversity of tree species (but greater variety of shrubs and other lesser plants).
• Response to either less total precipitation or less periodic precipitation.
• Many trees shed leaves at the same time, so more sunlight can penetrate.
• Produces classic jungle conditions.

Tropical Scrub

• Widespread in drier portions of A climatic realm (covers extensive areas in the tropics and subtropics).
• Dominated by low-growing scraggly trees and tall bushes, usually with an extensive understory of grasses.
• Plant species diversity is less than that in tropical rainforest and tropical deciduous areas.
• Faunal diversity is very different from that in tropical rainforest and tropical deciduous areas.
• Moderately rich assemblage of ground-dwelling mammals and reptiles, and of birds and insects.

Tropical Savanna

• Distribution of biome doesn’t exactly correlate with distribution of tropical savanna climate.
• Incomplete correlation is most noticeable where seasonal rainfall contrasts are greatest (which is associated with annual shifting of the Intertropical Convergence Zone [ITCZ]).
• Dominated by tall grasses.
• Some regions are actually former tropical deciduous forest and even tropical rainforest, but humans converted it through fires and by grazing domestic animals.
• Has a very pronounced seasonal rhythm: wet season, dry season, and wildfire season.
• Savanna fauna varies according to continent.
• Africa has the most remarkable, diverse large wildlife.
• Latin America has only a sparse population of large wildlife.

Desert

• Occurs extensively in midlatitude locations in Asia, North America, and South America, with a fairly close correlation to Bwh and Bwk climates.
• Vegetation is surprisingly variable.
• Shrubs are typical, with succulents common in drier parts.
• Trees can be found, particularly in Australia.
• Most deserts have a moderately diverse faunal assemblage.
• Variety of large mammals is limited.

Mediterranean Woodland and Shrub

• Six widely scattered and relatively small areas in the midlatitudes.
• Have pronounced precipitation—dry summer, wet winter.
• Dominant vegetation associations are physically similar, but taxonomically are quite varied.
• Dominated by dense growth of woody shrubs, but also have open, grassy woodlands.
• Plant species vary from region to region, but the trees and shrubs are primarily broadleaf evergreens.
• Many plants are adapted to rapid recovery after wildfire.
• Fauna are not particularly distinctive.
• Seed-eating, burrowing rodents are common.
• General overlap of animals between this biome and adjacent ones.

Midlatitude Grassland

• Locational coincidence between this biome and steppe climatic type is very pronounced in the Northern Hemisphere.
• Less distinct climatic correlations in the Southern Hemisphere.
• Occurs widely in the midlatitudes of North America and Eurasia.
• Low precipitation and/or frequency of fire prevent the growth of tree or shrub seedlings.
• Characteristics of grasses depend on moisture: taller in wetter areas (prairie); shorter in drier areas (steppe); and sometimes are not continuous, but grow in discrete tufts.
• Before human encroachment, fauna comprised large numbers of relatively few species, with migratory larger herbivores.

Midlatitude Deciduous Forest

• Used to be far more extensive in all Northern Hemisphere continents and to some extent in tracts in the Southern Hemisphere.
• Humans have cleared away large portions for agriculture.
• Fairly dense growth of tall broadleaf trees with a complete canopy in summer.
• Winter is very different, with seasonal fall of leaves.
• Tree species vary greatly from region to region.
• Generally has the richest assemblage of fauna in the midlatitudes.
• Seasonal variation of fauna (hibernation and migration).

Boreal forest—an extensive needleleaf forest in subarctic regions of North America and Eurasia; also called taiga.

• One of most extensive biomes, occupying a vast expanse of northern North America and Eurasia.
• Close correlation with subarctic climate.
• Has perhaps the simplest assemblage of plants.
• Most trees are conifers, though in some places deciduous trees interrupt the coniferous cover.
• Trees become spindlier, short, and openly spaced in the north.
• Bogs and swamps are numerous because of permanently frozen subsoil and derangement of normal surface drainage from past glaciers.
• Faunal diversity is limited because of the limited food supply.
• Populations of some species can fluctuate enormously in the space of a year or so.
• Insects are absent in winter but superabundant in the brief summer.

Tundra

• Distribution along the northern edge of Northern Hemisphere continents.
• Essentially a cold desert or grassland.
• No trees, but a considerable mixture of species (grasses, mosses, lichens, flowering herbs, and a scattering of low shrubs).
• Dominant animal life consists of bird and insects during summer.
• Few species of mammals and freshwater fishes, and almost no reptiles or amphibians.

Alpine Tundra

• Found in many high-elevation regions.
• Above the timberline there is sparse vegetation cover, consisting mostly of herbaceous plants, grasses, and low shrubs.

Human Modification of the Biosphere

Human activities severely alter the natural distribution patterns of biota.

Humans directly influence biotic distributions in three ways:

1. Physical removal of organisms
2. Habitat modification
3. Artificial translocation of organisms, or what is known as the introduction of exotic species.

• Physical Removal of Organisms
  • Humans severely modify the landscape, affecting both plants and animal inhabitants.
  • Cut down, plow up, pave over, burn out, poison, shoot, trap, otherwise eradicate.
• Habitat Modification
  • Humans affect native plants and animals by changing their habitat.
  • Humans change the soil environment through farming, grazing, engineering, and construction.
  • Humans degrade the atmospheric environment through pollution.
  • Humans impound, divert, and pollute waters.
• Introduction of Exotic Species
  • Humans have introduced many wild plants and animals into so-called new habitats.
  • Exotic species—organism that is introduced into habitats in which it did not naturally occur.
  • Sometimes deliberate, sometimes accidental.
  • Exotics have had great impacts (cats on flightless bird populations in New Zealand, European flea in all parts of the world).

Tropical Rainforest Removal

Over the past 40 years, tropical deforestation has become one of the most serious environmental problems.

The total extent of forest lost and exact deforestation globally are not precisely known.

Between 1990 and 2010, about 45 million hectares (111 million acres) of rainforest was cleared in Brazil, and Indonesia lost about 15 million hectares (37 million acres).

Annual rate of deforestation between 2000 and 2012 in Indonesia (0.84 million hectares per year) surpassed that of Brazil (0.46 million hectares per year).

Approximately 47 percent of equatorial Africa’s rainforest is now gone, as is about 45 percent of South and Southeast Asia’s, and close to 40 percent of Latin America’s.

Current situation varies in five major rainforest regions.

In the mid-1980s, extinction rates equated to about 1 species per day.

In the mid-1990s, extinction rates equated to about 2 species per hour.

Loss of forest also contributes to:

Accelerated soil erosion

Drought

Flooding

Water-quality degradation

Declining agricultural productivity

Greater poverty for rural inhabitants

Increasing atmospheric carbon dioxide (greenhouse effect)

Anticipated economic benefits are usually illusory.

Continuous heavy (and expensive) fertilization is necessary for sustainable agriculture.

Losing potential valuable resources—pharmaceutical products, new food crops, natural insecticides, industrial material, and crop hybridizations (for resisting disease, insects, parasites, and other environmental stresses).

Development of agroforestry (the planting of crops with trees) has counteracted some of the destruction.

UNESCO project to set aside reserves to protect biodiversity.

At present, about 651 biosphere reserves have been established in 120 countries.

Global rate of forest loss has generally decreased in many places during the past 10 years.

Replanting efforts are likewise expanding.

Net forest loss decreased from 8.3 million in 1990–2000 hectares per year to 5.2 million hectares per year in 2000–2010.

However, more recent studies suggest the FAO underestimated forest loss from 1990–2000.

However, replanted and naturally regenerated forests do not produce the same biodiversity as original forests.

Only about one-third of Earth’s forest cover is primary forest (forest with its natural species composition and few signs of human activity).

Global Environmental Change: Rainforest Loss in Brazil and Southeast Asia

More than half of all species reside in tropical rainforests.

Brazil is home the highest biodiversity in the world, followed closely by Indonesia.

Rainforest of Rondônio, Brazil, began experiencing deforestation by 1990 in a “fishbone”

Forest was being cleared for agriculture, ranching, and logging.

By 2012 the extent of deforestation was incredible.

More than 90 percent of agricultural land is used for cattle grazing or annual crops.

The greatest deforestation has shifted east and north to Mato Grosso and Pará.

Thus far, about 20 percent of the Amazon Rainforest has been cleared.

Since 2012, deforestation in Indonesia has outpaced that in Brazil.

Between 2000 and 2012, some 15 million acres of forest were removed for oil palm and pulp plantations.

Developers target carbon-rich wetlands for farming.

Draining and burning of wetlands releases carbon, produces air pollution, and displaces native species.

Local actions can influence global reactions.

The effects of tropical deforestation are global in scale.

People and the Environment: Invasive Species in Florida

Over the past 40 years, Florida has experienced massive in-migration of human population and major land use changes.

Natural ecosystems have since been destabilized, making them susceptible to invasive species.

A steady supply of exotic plants and animals has arrived in the past few decades.

Prominent among widespread exotic plant species is the melaleuca tree from Australia (“paperbark” trees).

Seeds were dispersed in the 1930s in the hopes of developing a timber industry.

The spread of the melaleuca has changed swamp to forest and radically altered ecosystems.

Spread of exotic weeds have been more extensive.

By the 1990s, hydrilla (Hydrilla verticillata), a native of tropical Africa and Southeast Asia, has clogged more than 60,000 hectares (150,000 acres) in Florida.

Recent mitigation efforts have greatly reduced its extent.