Environmental Science A Study of Interrelationships Twelfth Edition Enger & Smith Chapter 6 Kinds of Ecosystems and Communities Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Kinds of Ecosystems and Communities Outline . Succession . Biomes Are Determined by Climate . 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 Pioneer organisms 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 Primary succession on land 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 Succession Primary 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 Succession Secondary 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 Are Determined By Climate . 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 non-biological 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 Communities Biomes 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 Vegetation Relationship 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. Desert Temperate 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. Temperate 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. Temperate Grassland 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. Savanna 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. Mediterranean Shrubland (Chaparral) 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 from 50-200 cm. 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 Dry Forest 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. Tropical Rainforest 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