Outline Succession Biomes: Major Types of Terrestrial Climax Communities Major Aquatic Ecosystems
Succession Succession is a series of regular, predictable changes in community structure over time. Activities of organisms change their surroundings and make the environment suitable for other kinds of organisms. A climax community is a relatively stable, long- lasting community that is the result of succession. The kind of climax community that develops is primarily determined by climate.
Succession Primary succession begins with a total lack of organisms and bare mineral surfaces or water. Secondary succession begins with the disturbance of an existing ecosystem. • It is much more commonly observed, and generally proceeds more rapidly than primary succession.
Primary Succession Terrestrial primary succession • A pioneer community is a collection of organisms able to colonize bare rock (e.g., lichens). – Lichens help break down rock and accumulate debris, helping to form a thin soil layer. – The soil layer begins to support small forms of life.
Primary Succession Lichen community replaced by annual plants. Annuals replaced by perennial community. Perennial community replaced by shrubs. Shrubs replaced by shade-intolerant trees. Shade-intolerant trees replaced by shade-tolerant trees. Stable, complex, climax community eventually reached. • Each step in the process is known as a successional (seral) stage, and the sequence of stages is called a sere.
Primary Succession Climax communities show certain characteristics when compared with successional communities. • Climax communities maintain species diversity for an extended period. • They contain multiple specialized ecological niches. • They maintain high levels of organism interactions. • Climax communities recycle nutrients while maintaining a relatively constant biomass. The general trend in succession is toward increasing complexity and more efficient use of matter and energy.
Primary Succession Aquatic primary succession • Except for oceans, most aquatic systems are considered temporary. • All aquatic systems receive inputs of soil particles and organic matter from surrounding land. • This results in the gradual filling of shallow bodies of water. – Roots and stems below water accumulate more material. – Establishment of wet soil.
Primary SuccessionPrimary succession from a pond to a wet meadow.
Secondary Succession Secondary succession occurs when an existing community is disturbed or destroyed but much of the soil and some of the organisms remain. • Because the soil and nutrients remain, this process can advance more rapidly than primary succession. • Plants and organisms that survive the disturbance can grow quickly and reestablish themselves. • Nearby undamaged communities can serve as sources of seeds and animals. • The new climax community is likely to resemble the destroyed community.
Secondary SuccessionSecondary succession on land
Modern Concepts of Succession and Climax As settlers changed “original” ecosystems to agriculture, climax communities were destroyed. • Many farms were abandoned, and land began to return to its “original” condition. Ecologists began to recognize there was not a fixed, pre-determined community for each part of the world. • The only thing differentiating a climax community from any other successional community is its time scale.
Biomes: Major Types of Terrestrial Climax Communities Biomes are terrestrial climax communities with wide geographic distributions. • When different communities within a biome are examined, they will show differences in the exact species present, but the general structure of the ecosystem and the kinds of niches and habitats present are similar throughout.
Biomes: Major Types of Terrestrial Climax Communities Two primary nonbiological factors have major impacts on the kinds of climax communities that develop in any part of the world. • Temperature • Patterns of precipitation.
Biomes: Major Types of Terrestrial Climax CommunitiesBiomes of the world
The Effect of Elevation on Climate and Vegetation The distribution of terrestrial ecosystems is primarily related to precipitation and temperature. • Temperature is warmest near the equator and cooler toward the poles. • As altitude increases, average temperature decreases. • Moving from sea level to mountain tops, it is possible to pass through a series of biomes similar to what would be encountered moving from the equator to the North Pole.
The Effect of Elevation on Climate and VegetationRelationship between height above sea level, latitude, and vegetation.
Desert Deserts are areas that average less than 25 cm annual precipitation. • Unevenly distributed throughout the year. They are likely to be windy. They experience large daily temperature fluctuations. There is infrequent cloud cover. There are many species, but they are present in low numbers. Many species exhibit specialized adaptations to climate, such as the ability to conserve water.
Desert Human impact on deserts: • Humans have historically had little impact on deserts. • Modern technology allows for the transport of water to the desert. • This has resulted in the development of cities in some desert areas and some limited agriculture as a result of irrigation.
Grassland Temperate grasslands, also known as prairies or steppes, are widely distributed over temperate parts of the world. They typically receive 25 -75 cm of annual precipitation. Fire is an important force in preventing the invasion of trees and releasing nutrients from dead plants to the soil. The primary consumers are large herds of migratory grazing mammals. Many insect species are also common.
Grassland Human impact on grassland: • Most of the moist grasslands of the world have been converted to agriculture. • Most of the drier grasslands have been converted to the raising of domesticated grazers like sheep, cattle, and goats. • Little undisturbed grassland is left, and those fragments that remain need to be preserved as refuges for the grassland species that once occupied huge portions of the globe.
Savanna Savannas are found in tropical parts of Africa, South America, and Australia. They are characterized by extensive grasslands spotted with occasional patches of trees. They receive 50-150 cm annual precipitation, unevenly distributed throughout year. Rainfall patterns produce a seasonally structured ecosystem. Fire is a common feature. Many trees are involved in nitrogen fixation.
Savanna Human impact: • Savannas have been heavily impacted by agriculture. • Because of long periods of drought, raising crops is difficult without irrigation. • Some areas support nomadic herding. • In Africa, there are extensive areas set aside as parks and natural areas and ecotourism is an important source of income.
Mediterranean Shrublands (Chaparral) Mediterranean shrublands are located near oceans and are dominated by shrubby plants. Their climate features wet, cool winters and hot, dry summers. They receive 40-100 cm annual precipitation. This biome is typical of the Mediterranean coast, coastal southern California, as well as parts of Africa, Chile, and Australia. Vegetation is dominated by woody shrubs adapted to hot, dry summers. Fire is a common feature.
Mediterranean Shrublands (Chaparral) Human impact: • Very little undisturbed Mediterranean shrubland still exists. • Agriculture is common, often with the aid of irrigation. • Major cities are located in this biome.
Tropical Dry Forest The tropical dry forest is another biome heavily influenced by seasonal rainfall. These biomes are found in Central and South America, Australia, Africa, and Asia. Annual precipitation ranges 50-200cm. Many exhibit a monsoon climate with highly seasonal rainfall. Plants have developed special adaptations to survive drought.
Tropical Dry Forest Human impact: • Many of these forests occur in areas of very high human population. • Harvesting of wood for fuel and building materials has heavily affected these forests. • Many of the forests have been converted to farming or the grazing of animals.
Tropical Rainforest Tropical rainforests are located near the equator where temperature is relatively warm and constant. Most areas receive 200+ cm annual rainfall, and some receive in excess of 500 cm. The soil allows high levels of leaching, thus most nutrients are tied up in biomass. Tropical rainforests have a multi-layered canopy. • Epiphytic plants They also host a very high diversity of species.
Tropical Rainforest Human impact • Tropical rainforests are under intense pressure from logging and agriculture. • Many of the countries where tropical rainforests occur are poor and seek to obtain jobs and money by exploiting this resource. • Forestry can be a sustainable activity, but in many cases it is not.
Temperate Deciduous Forest Temperate deciduous forests are typical of the eastern half of the United States, south-central and southeastern Canada, southern Africa, and many parts of Europe and Asia. These areas receive 75-100 cm annual precipitation, evenly distributed throughout the year. Trees typically lose their leaves during the winter and replace them the following spring.
Temperate Deciduous Forest This biome features mild winters and a long growing season (6 months). In contrast to tropical rainforests, where individuals of a tree species are scattered throughout the forest, temperate deciduous forests have many fewer species; some may have two or three dominant tree species.
Temperate Deciduous Forest Human impact: • Most of the temperate deciduous forests have been heavily affected by human activity. • Much has been cleared for farming. • Much of the current forest is subjected to periodic logging. • Major populations centers of eastern North America and Europe are in areas that were originally temperate deciduous forest.
Taiga, Northern Coniferous Forest, or Boreal Forest Throughout the southern half of Canada, parts of northern Europe, and much of Russia, there is an evergreen coniferous forest known as the taiga, northern coniferous forest, or boreal forest. This biome receives 25-100 cm precipitation annually.
Taiga, Northern Coniferous Forest, or Boreal Forest It features short, cool summers and long winters with abundant snowfall. The climate is humid because of the great deal of spring snowmelt; low temperatures reduce evaporation. The trees are adapted to winter conditions: • Needle-shaped leaves prevent water loss. • Flexible branches
Taiga, Northern Coniferous Forest, or Boreal Forest Human impact: • Human impact is less severe than with many other biomes because population density is low. • Logging is common. • Herding of reindeer occurs in northern Scandinavia.
Taiga, Northern Coniferous Forest, or Boreal Forest
Tundra North of the taiga is the tundra, an extremely cold region that lacks trees and has a permanently frozen subsurface soil. The permanently frozen soil layer is called permafrost. The tundra receives less than 25 cm annual precipitation.
Tundra This biome has a short, wet summer. Waterlogged soils and shallow ponds and pools are present in spring and summer. Plants are usually less than 20 cm tall. Tundralike communities known as alpine tundra are found on mountaintops throughout the world.
Tundra Human impact: • Few people live in this region. • Local native people often rely on subsistence hunting for food. • Because of the very short growing season, damage to this kind of ecosystem is slow to heal, so the land must be handled with great care.
Major Aquatic Ecosystems Aquatic ecosystems are shaped by key environmental factors: • The ability of the sun’s rays to penetrate the water • Depth of the water • The nature of the bottom substrate • The water temperature • The amount of dissolved salts.
Major Aquatic Ecosystems Aquatic ecosystems with little dissolved salt are called freshwater ecosystems. Marine ecosystems have a high dissolved salt content.
Marine Ecosystems The pelagic region is the open sea above the sea floor. The euphotic zone is the upper layer of ocean where the sun’s rays penetrate. Phytoplankton are microscopic plants floating in the ocean (perform photosynthesis). Zooplankton are microscopic animals of many kinds that feed on phytoplankton. Productive aquatic ecosystems contain a plentiful supply of essential nutrients.
Marine Ecosystems Benthic marine ecosystems • Benthic organisms, attached or non-attached, live on the ocean bottom. • Substrate and temperature are very important characteristics in determining benthic community development. • An abyssal ecosystem is a benthic ecosystem that occurs at great depths in the ocean. – There is no light to support photosynthesis. – Animals are scavengers; many are small and generate light for finding or attracting food.
Marine Ecosystems The substrate is important in determining the kind of benthic community that develops. • Large plants and algae cannot become established in shifting sand substrate. • Mud usually contains little oxygen but is a good substrate for some kinds of rooted plants. • Rocky surfaces in the ocean provide a good substrate for many kinds of algae. – A profuse growth of algae is associated with a large variety of animals.
Marine Ecosystems Coral reef ecosystems are composed primarily of coral animals that build cup-shaped external skeletons. Corals contain single-celled algae and carry on photosynthesis. They require warm water, thus are found only near the equator. Most require clear, shallow water with ample sunlight penetration.
Marine Ecosystems Mangrove swamp ecosystems are tropical forest ecosystems that occupy shallow water near the shore and adjacent land. Their trees tolerate high salt content and excrete salt from their leaves. They have extensively developed roots that can extend above water. The trees trap sediment in shallow areas, which results in the development of terrestrial ecosystems.
Marine Ecosystems Estuaries consist of shallow, partially enclosed areas where freshwater enters the ocean. Organisms are specially adapted to varying levels of salinity from tides and river flow. Estuaries are extremely productive ecosystems because areas are shallow, warm, and nutrient- rich. These areas are important nursery sites for fish and crustaceans.
Marine Ecosystems Human impact: • Oceans cover about 70% of the Earth’s surface. • Overfishing has destroyed many of the traditional fishing industries of the world. • Fish farming results in the addition of nutrients and has caused diseases to spread from farmed fish to wild fish. • Estuaries are affected by fertilizers, animal wastes, and pesticides that flow down rivers from farmland. • Use of the oceans as transportation results in oil pollution and trash floating onto the shore.
Freshwater Ecosystems Freshwater ecosystems may be divided into two broad categories: • Stationary water (lakes, ponds, and reservoirs) • Running water (streams and rivers)
Freshwater Ecosystems Lakes and Ponds • The littoral zone of a lake is the region of a lake with rooted vegetation. – Emergent plants have leaves that float on, or protrude above, the water’s surface. – Submerged plants stay submerged below the water’s surface. • The limnetic zone is the region of lake with no rooted vegetation.
Freshwater Ecosystems The productivity of a lake is determined by many factors. • Cold temperature reduces rate of photosynthesis. • Shallow water allows more photosynthesis. • Erosion from land increases nutrient levels. • Dissolved oxygen, input via wave action and photosynthesis from aquatic plants, determines the kinds of organisms that can inhabit the lake.
Freshwater Ecosystems Lakes and Ponds • Oligotrophic lakes are deep, cold, nutrient-poor. • Eutrophic lakes are shallow, warm, nutrient-rich. • Biochemical oxygen demand (BOD) is the amount of oxygen used by decomposers to break down a specific amount of organic matter.
Freshwater Ecosystems Streams and Rivers • Even though most streams are shallow, it is difficult for most photosynthetic organisms to accumulate nutrients necessary for growth. – Most clear streams are not very productive. – Most debris is input from terrestrial sources. • Periphyton is the collection of algae, animals and fungi attached to rocks and other objects on the bottom.
Freshwater Ecosystems Streams and Rivers • Swamps are wetlands containing trees able to live in environments that are permanently flooded, or flooded most of the year. • Marshes are wetlands dominated by grasses and reeds. • Many swamps and marshes are successional states that eventually become totally terrestrial communities.
Freshwater Ecosystems Human impact: • Most freshwater ecosystems have been heavily affected by human activity. • Any activity that takes place on land ultimately affects freshwater because of runoff from the land. • Agricultural runoff, sewage, sediment, and trash all find their way into streams and lakes.
Summary Ecosystems change as one kind of organism replaces another in a process called succession. The climax community is a relatively stable stage. Major regional terrestrial climax communities are called biomes. Primary determiners of the kinds of biomes that develop are temperature and yearly rainfall distribution.
Summary Major biomes are desert, grassland, savanna, Mediterranean shrublands, tropical dry forest, tropical rainforest, temperate deciduous forest, taiga, and tundra. Aquatic ecosystems can be divided into marine (saltwater) and freshwater ecosystems. The shore substrate determines the mixture of organisms that can live there. Lakes have a structure similar to that of the ocean, but with different species.