Chapter 6: Kinds of Ecosystems and Communities

Transcription

1 Chapter 6: Kinds of Ecosystems and Communities Succession 1) Ecosystems: Dynamic, changing units. 2) Abiotic Factors: temperature, rainfall, intensity of sunlight, seasonality. (Chap 5) Biotic Factors: Include all forms of life with which it interacts. (Chap 5) It s possible, over long time period, to see trends in the way the structure of a community changes and to recognize that climate greatly influences the kind of community that becomes established in an area. Succession: 1) The concept that communities proceed through a series of recognizable, predictable changes in the structure over time. 2) It occurs because the activities of organisms cause changes in their surroundings that make the environment suitable for other kinds of organism. 3) When new species become established, they compete with the original inhabitants. 4) The original species may be replaced completely or become less numerous as invading species take a dominant role. 5) Factors that determine succession: climate, locally available seed sources, frequency of disturbance, and invasions of organisms from outside the area. 6) Process is not always predictable as once was believed. 7) Two kinds of succession: Primary and secondary. Climax community: 1) A relatively stable, long-lasting community that is the result of succession. 2) Traditionally, the way a climax community developed is primarily determined by climate. (e.g. forest, grassland or deserts) 3) Factors that determine the climax community: substrate/soil, water, climate, colonizing organisms (Fig. 6.1) Primary Succession Terrestrial Primary Succession: 1) A successional progression that begins with a total lack of organisms and bare mineral surfaces or water. (Ex. Begin on a bare rock surface, in pure sand, or in standing water) 2) Condition occurs: Volcanic activity causes lava flows or glaciers scrape away the organisms and soil. Lowering of sea level exposes new surfaces for colonization by terrestrial organisms. 3) Takes an extremely long time: because no soil and few readily available nutrients for plants to use for grow. 4) Factors that determine the rate of succession and the kind of climate community: The kind of substrate (rock, sand, clay) will greatly affect the kind of soil that will develop. The kinds of spores, seeds, or other reproductive structures will determine the species available to colonize the area. The climate will determine the species that will be able to live in an area and how rapidly they will grow. The rate of growth will determine how quickly organic matter will accumulate in the soil. The kind of substrate, climate, and amount of organic matter will influence the amount of water available for plant growth. 5) Stages involved: (Fig. 6.3) Pioneer Stages: Windblown spores or other tiny reproductive units of a few kinds of organisms can become established and survive in the inhospitable environment. The collection of organisms is known as the pioneer community. The inhospitable environments are bare rock or sand, no soil, little moisture, damaging wind, few nutrients available, temperature changing drastically, few places to hide or attach. Common organisms: 1

2 Lichens: mutualistic relationship between two kinds of organisms: (algae or bacteria: carry on photosynthesis, and fungi: attach to rock and retain water). The growth and development of lichens (e.g. producers) is a slow process. Factors contributing to accumulation of a thin layer of soil: (1) Acid produced by lichens breakdown the rock (2) Physical and chemical weathering process fragment the rock (3) Trapping the debris (4) Contribution of organic matter by the death of lichens and other organisms. Later Stages: The thin layer of soil is the key to the next stage in the successional process. The layer retain some water, support some fungi, certain worms, insects, bacteria, protozoa, and perhaps a few tiny plants that live only one year but produce flowers and seeds that fall to the soil and germinate the following growing season. As these organisms grow, reproduce and die, they contribute additional organic material for the soil-building process, and the soil layer increases in thickness and is better to retain water. Annual plants are dominate in this stage but are replaced by perennial grasses and herbs, which are often replaced by larger perennial woody shrubs and are in turn replaced by larger trees that require lots of sunlight, and in turn replaced by trees that can tolerate shade. Eventually, a relatively stable, long-lasting, complex, and interrelated climax community of plants, animals, fungi, and bacteria is produced. Successsional stage or seral stage: each step in this process from pioneer community to climax community. Sere: the entire sequence of stages, from pioneer community to climax community. Differences Between Successional and Climax Communities: Characteristics Climax Community Successional Community 1) Species 2) Time scale (p. 111) 1) Maintaining the mix of species for a long time 2) Slowly 1) Maintaining the mix of species only temporary 2) Rapidly Niches Many specialized niches More generalized niches Organisms Have more kinds of organisms and kinds of interactions among organisms Less kinds of organisms and kinds of interactions among organisms Nutrients and biomass Tend to recycle nutrients and maintain relatively constant biomass Tend to accumulate large amount of new material. Aquatic Primary Succession 1) Principle concepts of land succession can be applied to aquatic ecosystem. 2) Exception: Most of aquatic ecosystems are considered temporary, as eventually they wil disappear and be replaced by terrestrial ecosystem as a result of normal successsional processes. Early Stages Aquatic Vegetation: 1) Initially only floating plants and algae can exist. 2) As sediment accumulates, it becomes possible for certain species of submerged plants to establish their roots in the sediments of the bottom of shallow bodies of water. They can carry on photosynthesis, resulting in a further accumulation of organic matter. 2

3 3) Plants tend to trap more sediment that flow into the pond or lake, resulting in a further decrease in water depth. Eventually, emergent plants become established. They have leaves float on the surface or project into the air. 4) As the process continues, a wet soil is formed and grasses and other plants can live in wet soil become established. Later Stages Transition to Terrestrial Communities (Fig. 6.4) 1) Also called as a wet meadow. 2) Plants tend to draw moisture from the soil, and as more organic matter is added to the top layer of the soil, it becomes drier, which set for a typical terrestrial successional series of changes, eventually resulting in a climax community typical for the climate of the area. Observing Aquatic Succession: 1) In the central, deeper portions of lake: only floating plants and algae. 2) Near the shore, submerged plants (i.e. Elodea and algal mats) emergent vegetation (i.e. water lilies and cattails) grasses and sedges that tolerate wet soil on the share, the beginnings of a typical terrestrial succession resulting in the climax community typical for the area. 3) In many northern regions, sphagnum moss forms thick, floating mats that can be colonized by plants that tolerate wet soils. A network of roots ties the mat together to form a floating community (or bog). (Fig. 6.5) Secondary Succession Same processes and activities as in primary succession. Major difference: secondary succession occurs when an existing community is destroyed but much of the soil and some of the organisms remain. Causes: A forest fire, a flood, or the conversion of a natural ecosystem to agriculture. Rate: More rapidly than primary succession: soil remains and nutrients are still available. The new climax community is likely to resemble the one that was destroyed (Fig. 6.6): Some plants and organisms may survive and the undamaged communities adjacent to the disturbed area can serve as sources of seeds and animals that migrate into the disturbed area. Modern Concepts of Succession and Climax: Previous discussions: oversimplification of the true nature of the process. Ex. 1) European explorers or settlers removed the original forests and grasslands and converted to farming, the original climax community was destroyed. 2) Many farmers abandoned the land as poor farming practices destroyed the soil. The land was allowed to return to its original condition. This secondary succession often resulted in forests resembled those that had been destroyed. However, in some cases, these successional forests (also called climax communities) contained fewer species and were entirely different kinds of communities from the originals. 3) The introduction of species, on purpose or accidentally, from Europe and other parts of the world changed the mix of organisms that might colonize an area. Today, some communities are dominated by these introduced species including diseases. 4) Land is unable to return to preordained climax condition. Many human activities (e.g. agricultural practices, logging, damming, flooding) alter the nature of the successional process. Though the climax concept embraces the false notion (i.e. there is a specific end point to succession), it is still important to recognize that there is an identifiable, predictable pattern of change during succession and that later stages in succession are more stable and longer lasting than early stages. It s not really important whether we call a specific community of organisms a climax community or not. Biomes: Major Types of Terrestrial Climax Communities 1) Biomes: Terrestrial climax communities with wide geographic distribution. (Fig. 6.7) 3

4 2) Two primary nonbiological factors that determine climax community: Precipitation pattern: Total amount of precipitation per year The form (rain, snow, sleet) in which it arrives Its seasonal distribution (spread evenly or concentrated at particular time) Temperature pattern: (Fig. 6.8) Tropical Area: relatively unchanging temperature around the year Near Poles Area: long winter with extremely cold temperature and relatively short, cool summer. Other Area: evenly divided between cold and warm periods of the year. 3) Other factors: Periodic fire: important in maintaining grassland and shrub climax community by preventing establishment of larger, woody species. Frequent, strong wind: Preventing the establishment of trees and cause rapid drying pf the soil. Type of soil: Sandy soils dried out quickly not allowing the establishment of more waterdemanding species (trees). Extremely wet soils may allow only certain species of tree to grow. The Effect of Elevation on Climate and Vegetation 1) Precipitation and temperature are primarily related to distribution of terrestrial ecosystem. 2) At the equator, it s possible to pass a series of biomes that is similar to what would be encountered as one traveled from the equator to the North Pole when the height above sea level increases. (Fig 6.9) Deserts: Found throughout the world. Climate: Sahara Desert and the deserts of the southwestern United States and Mexico: hot. Gobi Desert and the deserts of northwestern United States: cold. Temperature: High (hot) during the day; low (cold) during the night. Primary Factor: Lack of water. Average less than 25 cm (or 10 inches) of precipitation per year. Forms of precipitation: snow or rain in winter months; rains as heavy thundershower. Rate of evaporation: high and thus likely to be windy. Plant growth and flowering: usually coincide with the periods when moisture is available. Organisms: Many species but low numbers of individuals live in the desert. Ex. Plants: 1) have very small leaves or none during the driest season 2) have significant amount of space between them 3) have some parts or seeds lie dormant until rains come. 4) grow rapidly, reproduces and die or become dormant until the next rains. 5) many are spiny discouraging large animals from eating the leaves and young twigs. Animals: 1) populations: low and size: small. 2) inactive during the hot part of the day or in underground burrows to conserve water. 3) able to survive with minimal amount of water. Human Impact: 1) Little impact: as harshness not allowing agriculture. 2) Hunter-gatherer societies: the most common ones associated with deserts. Nomadic herding: herders move their livestock to find patches of vegetation for grazing. 4

5 Modern technology: allowing transport of water to the desert resulting in the development of cities in some desert areas and some limited agriculture as a result of irrigation. Grassland: Temperate grassland (i.e. prairies or steppes) widely distributed over temperate parts of the world. Receiving 25 to 75 cm (10 to 30 inches) of precipitation per year. Windy with hot summers and cold-to-mild winters. Fire is an important force in preventing the invasion of trees and releasing nutrients from dead plants to the soil. Organisms: Grasses: make up 60-90% of the vegetation with other kinds of flowering plants interspersed with them. Usually their roots form a network that binds soil together. Trees, requiring greater amount of water, are rare in the region except along watercourses. Primary consumers are grazing animals, which in turn supply fertilizers from their dung and discourage invasion by woody plants by eating the young roots. Other species: grasshoppers, other herbivorous insects, dung bettles, and kinds of flies, and birds. Human Impact: Moist grasslands: converted to agriculture for corn and wheat due to its rich, deep soil. Drier grasslands: converted to the raising of domesticated grazers (cattle, sheep and goats). Undisturbed grassland: few, served as refuges for the grassland species. Savanna: (Fig. 6.12) Found in tropical parts of Africa, South American and Australia. Characteristics: extensive grasslands spotted with occasional trees or patches of trees. Receive cm (20-60 inches) of rain, not distributed evenly throughout, per year. A very seasonal ecosystem: a period of heavy rainfall followed by a prolonged drought. Organisms: Plants and animals time their reproductive activities to coincide with the rainy period. Predominant plants: grasses. Other plants: drought-resistant flat-topped, thorny trees are common. Common feature: Fire. Trees: resistant to fire damage; nitrogen-fixing (legumes). Other species: wallabies, zebras, elephants, capybaras (rodents), lions, birds, insects, mound-building termites. Human Impact: Heavily by agriculture. Moist regions: farming. But difficult without irrigation due to long periods of drought. Drier regions: raising livestock or nomadic herding. In Africa: extensive areas set aside as parks and natural areas, and ecotourism is an important source of income. Constant struggle between agriculture, grazing and preserve it in a more natural state. Mediterranean Shrublands (Chaparral): Located near oceans and are dominated by shrubby plants. Wet cool winters and hot, dry summers. Rainfall: cm (15-40 inches) per year. 5

6 Found in coastal southern California, the southern tip of Africa, a portion of the west coast of Chile, and southern Australia. Organisms: Woody shrubs: withstand the hot, dry summer (Fig. 6.13). Plants are dormant during the summer. Shrubs are adapted to withstand occasional fires. Common feature: fire. Animals: vary widely in the different regions of the world, such as insects, reptiles, birds, rattlesnakes, spiders, coyotes, lizards, and rodents. Human Impact: Heavily altered by human activity due to mild climate and closeness to the ocean. Agriculture is common with the aid of irrigation resulted many major cities. Tropical Dry Forest: Heavily influenced by seasonal rainfall. Found in parts of Central and South America, Australia, Africa, and Asia (particularly India and Myanmar). Monsoon climate: several months of heavy rainfall followed by extensive dry periods ranging from few to as many as eight months.. Rainfall: highly seasonal: cm (20-80 inches) per year. Organisms: Plants: drop their leaves during the dry period. Animals: found here also found in more moist tropical rainforests of the regions. But fewer kinds than in rainforests. Human Impact: In area of heavy human population. Harvesting wood for fuel and building materials. Converting to farming or the grazing of animals. Tropical Rainforest: Located in near the equator in Central and South America, Africa, Southeast Asia, and some islands in the Caribbean Sea and Pacific ocean. (Fig. 6.15) Normally warm and relatively constant. Rainfall: most areas > 200 cm (80 inches); some area > 500 cm (200 inches) per year. Organisms: A greater diversity of species than any biome. Plants: 1) Grow very rapidly due to warm temperature and abundant rainfall. 2) Have extensive root networks, associate with fungi, near the surface of soil, allowing them to catch nutrients from decaying vegetations before the nutrients are washed away. 3) Hundreds of species of trees within a few km 2. 4) > km between two individuals of the same species. 5) Home to a set of animals and plants (ferns, mosses and orchids) that use trees as food, shelter or support. 6) Only shade-tolerant plants live beneath the trees canopy. 7) Vines attached to supporting trees and compete for sunlight. 8) Source of new nutrients: rainfall as atmospheric particles and gasses dissolve as the rain fall. Insects: ants, termites, moths, butterflies, and beetles. Animals: mammals, lizards, tree frogs, nectar and fruit-feeding birds, etc. Soils: poor in nutrients as water tends to carry away any nutrients not immediately taken up by plants. Communication between animals: by making noise due to low light levels and difficult of maintaining visual contact with other animals. 6

7 Human Impact: Tropical rainforests suffer Intensive logging and agriculture. Many countries with tropical rainforests are poor and seek to obtain jobs and money by exploiting this resource. Agriculture is not successful as nutrients are in biomass, not in the soil, and high rainfall quickly carries away the nutrients. Poor people: 1) Raising food by burning the forest and raising crops for a year or two. 2) Forest are cleared for cattle ranching. Temperate Deciduous Forest Have a winter-summer change of the season. Typical in the major population centers: eastern half of U.S.A., parts of south central and southeastern Canada, southern Africa, and many areas of Europe and Asia. Receive cm (30-60 inches) of evenly distributed precipitation per year. Winter: mild. Organisms: Plants: 1) Actively grow for about half the year. 2) Fewer species: common ones are maples, aspen, birch, beech, oaks, and hickories in North America and Europe. 3) Wildflowers bloom in spring before leaves come out from tall trees. Birds: 1) Most are primarily migrants that arrive in spring, raise their young during the summer and leave in the fall. 2) Year-round residents: woodpeckers, grouse, turkeys and some finches. Amphibians and reptiles: pray on insects and other small animals (mice, squirrels, moles, etc.) Predators: foxes, badgers, weasels, coyotes, etc. Human Impact: Heavily affected: farming and periodic logging. Taiga, Northern Coniferous Forest, or Boreal Forest (Fig. 6.17) i.e. evergreen coniferous forest. Throughout the southern half of Canada, parts of northern Europe, and much of Russia. Short, cool summers and long winters (extremely harsh, ~ 6 months) with abundant snowfall. Receive cm (10-40 inches) per year. Winter: dry. Spring: humid due to a great deal of snowmelt and low temperatures reduce evaporation. Landscape: dotted with lakes, ponds and bogs. Organisms: Plants: 1) Conifers: spruces, firs and larches are common trees. 2) Needle-shape leaves to prevent water loss. 3) Branches are flexible allowing to bend under a load of snow, which slides off the pyramid-shape trees without damaging them. Birds: 1) Most are primarily migrants and feed on abundant summer insect population. 3) Year-round residents: woodpeckers, grouse, and owls. Animals: deer, caribou, moose, wolves, weasels, mice, snowshoe hares, and squirrels. Human Impact: Less severe: due to low population density. Common activity: logging, some herding of reindeer in northern Scandinavia. Native peoples: rely on subsistence hunting for food. 7

8 Tundra (Fig. 6.18) North of taiga, an extremely cold region. Permanently frozen subsurface soil (i.e. permafrost); no trees. Precipitation: < 25 cm (10 inches) per year. Summer: < 10 o C (50 o F) reducing evaporation rate, wet as snows melt. Winter: up to 10 months, extremely cold and windy. Waterlogged soil, many shallow ponds and pools. Organisms: Plants: grasses, dwarf birch, dwarf willow; short, < 20 cm (8 inches). Insects: common during the summer; serving as food for migratory birds. Birds: ducks and geese: migrate to tundra in spring; mate and raise their young during the summer; migrating to south in the fall. Mammals: hardy. Musk oxen, caribou (reindeer), arctic hare, and lemmings. Predators: arctic foxes, wolves, and owls. Alpine tundra: 1) Scattered patches of tundralike communities on mountaintops. 2) Birds and animals migrate up to alpine tundra during the summer and return to lower elevations when weather turns cold. Human Impact: Local native people rely on subsistence hunting for food. Slow to heal if the ecosystem is damaged due to very short growing season. Major Aquatic Ecosystems Important factors: 1) the ability of sun s rays to penetrate the water 2) the depth of water 3) the nature of the bottom substrate 4) the water temperature 5) the amount of dissolved salts/nutrients to be used in photosynthesis Ecosystems: 1) Freshwater ecosystems: having little dissolved salt 2) Marine ecosystems (Fig. 6.19): Having high salt content Pelagic Marine Ecosystems: the ecosystem that the pelagic organisms (not attached to the bottom of the ocean, actively swimming) belong to. Plankton: very small aquatic organisms, weakly swimming, carried by currents. Phytoplankton: small, microscopic floating algae and bacteria are planktonic organisms, carrying on photosynthesis in euphotic zone. Euphotic zone: 1) the upper layer of ocean where sun s ray can penetrate. 2) thickness depending on the clarity of the water, ~ 150 m (500 ft) in depth. Zooplankton: 1) small, weakly swimming animals, feed on phytoplankton. 2) in greater depth of ocean but migrate upward at night and feed on phytoplankton. 3) eaten by larger animals (fish, large shrimps), which are eaten by larger fish (salmon, tuna, sharks and mackerel) Benthic Marine Ecosystems: the ecosystem that the benthic organisms (whether attached or not to the bottom) belong to. Benthic organisms: some fish, clams, oysters, various crustaceans, sponges, and others live on the bottom. 1) In shallow water: seaweeds are common as sunlight can penetrate to perform photosynthesis. 2) Substrate and temperature respectively determine the development and establishment of the kind of benthic community. Ex. Sand: difficult for large plants or algae to establish as it shifts and moves. 8

9 Mud: suitable habitat for rooted plants like mangrove trees and sea grasses. Warm water: suitable for coral reefs (near equator, shallow clear water) or mangrove swamps. 3) Coral reef ecosystem: (Fig. 6.21) I. Produced by coral animals that build cup-shaped external skeletons around themselves. II. Corals protrude from their skeletons to capture food and expose themselves to the sun, which allows single-celled algae living in their bodies to perform photosynthesis to provide nutrients to both. (Mutualistic relationship) III. Coral skeletons provide a living surface for many other kinds of animals. Some eat corals directly, some feed on small skeletons or algae. IV. Members include fish, sponges, clams, snails, crustaceans, etc. 4) Mangrove swamp ecosystem: (Fig. 6.22) I. Tropical forest ecosystems that occupy shallow water near the shore and the adjunct land. II. Organisms: special kinds of trees, excreting salt from their leaves, which can tolerate the high salt content of the ocean. III. Trees can become established when water is shallow and wave action is not too great. Germinated seed falls from tree, floats in the water, and become trapped in mud and takes root and trap sediment and provide places for living. (fish, crabs, jellyfish, oysters, etc.) 5) Abyssal ecosystem: I. Occurs at great depths in the ocean. II. No light to support photosynthesis. III. Rely on a continuous rain of organic matter from euphotic zone. IV. Organisms are eventually scavengers. V. Animals: small and generate light for finding or attracting food. 6) Estuaries: I. A special category of aquatic ecosystem, consisting shallow, partially enclosed area where freshwater enters the ocean. II. Saltiness of water in the estuary changes with tide and the flow of water from rivers. III. Organisms: Adapted to the condition and the number of species are less than in the ocean or in freshwater. IV. Productive: o Large amounts of nutrients introduced into the basin from rivers. o Light penetrates shallow water to allow photosynthesis by phytoplankton, algae and plants. o A nursery site for fish and crustaceans (flounders and shrimp) Human Impact on Marine Ecosystems: 1) Overfishing: destroy the traditional fishing industries. 2) Fish farming: adding nutrients and has caused diseases to spread from farmed species to wild fish. 3) Estuaries: important fishing areas but affected by the flow of fertilizers, animal waste and pesticides. 4) Mangroves: converted to fishing farms. Freshwater Ecosystems Differences from marine ecosystems: 1) Amount of salt present: much less 2) Temperature of water: can change greatly 3) Water is in the process of moving to the ocean 4) Oxygen is often in short supply 9

10 5) Organisms inhabit are different from the marine ecosystem Two categories: stationary (lakes, ponds)and running (streams, rivers) 1) Lakes and Ponds: Emergent plants: a) plants that have leaves float on the surface. b) protrude above the water. c) cattails, bulrushes, arrowhead plants, water lilies, etc. Submerged plants: a) rooted plants that submerged below the surface of the water b) Elodea, Chara, etc. Littoral zone: the portion of lake that has rotted vegetation. Limnetic zone: the portion of lake that does not have rooted vegetation. Productivity: determining by several factors: 1) Temperature: cold temperature reduces photosynthesis 2) Water depth: shallow lake, tend to be warmer, can have light penetrating to the lake bottom and thus the photosynthesis can occur throughout the entire water. 3) Amount of nutrients present: primarily determined by streams and rivers that carry nutrients to the lakes. Human activities: farming and construction: expose soil and release nutrients Depositing sewage into streams and lakes Kinds of lakes: a) oligotrophic: deep, clear, cold, nutrient-poor, low productivity b) eutrophic: shallow, murky, warm, nutrient-rich Biochemical oxygen demand (BOD): p ) Dissolved oxygen content of water determines the kinds of organisms that can inhabit the lake. 2) The amount of oxygen used by bacteria and fungi to decompose or break down organic molecules that enter water is called BOD. 3) In winter, many bodies of water experience a reduced oxygen level when producers die. 4) The amount and kinds of organic matters determine how much oxygen is left to be used by other organisms (fish, crustaceans, snails, etc.) 2) Streams and Rivers: Periphyton: a) the collection of attached algae, animals, and fungi. b) not very productive even though water is shallow, light can penetrate, difficult to accumulate nutrients for grow as water is running c) major source of nutrients: falling organic matters, primary leaves, bodies of living and dead insects. Swamps: wetlands that contain trees that are able to live in places that are either permanently flooded or flooded for a major part of the year. Marshes: wetlands that are dominated by grasses and reeds. Human Impact on Freshwater Ecosystems: Agricultural runoff, sewage, sediment, trash, etc. 10