Ecology = Scientific study of natural communities Process Pattern begets Observations Hypotheses Principles Predictions Experimental and observational tests suggest delimit lead to provisionally accept, revise or reject are tested by made of

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Types of Terrestrial Ecosystems Biomes are major groupings of plant and animal communities defined by a dominant vegetation type. Each biome is associated with a distinctive set of abiotic conditions. The type of biome present in a terrestrial region depends on climate—the prevailing, long-term weather conditions found in an area. Weather consists of the specific short-term atmospheric conditions of temperature, moisture, sunlight, and wind.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Distinct Biomes Are Found throughout the World Barrow Dawson Konza Prairie Chicago Yuma Belém

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Solar Radiation per Unit Area Declines with Increasing Latitude Low angle of incoming sunlight Moderate angle of incoming sunlight Sunlight directly overhead Large amount of sunlight per unit area Small amount of sunlight per unit area North pole

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Global Air Circulation Patterns Affect Rainfall Circulation cells exist at the equator … Atmosphere (not to scale) Hadley cell Hadley cell Cooled air is pushed poleward Warm air rises and cools, dropping rain Dense, dry air descends, warms, and absorbs moisture

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Global Air Circulation Patterns Affect Rainfall … and at higher latitudes. There are also three circulation cells in the Southern Hemisphere (draw them in) There are three circulation cells in the Northern Hemisphere

Figure 50-11

Figure Tropical wet forests are extremely rich in species

Figure 50-13

Figure Saguaro cacti are a prominent feature of the Sonoran Desert in the southwestern part of North America

Figure 50-15

Figure Grasses are the dominant lifeform in prairies and steppes

Figure 50-17

Figure Temperate forests are dominated by broad- leaved deciduous trees

Figure 50-19

Figure Boreal forests are dominated by needled-leaved evergreens, such as spruce and fir

Figure 50-21

Figure Arctic tundra is dominated by cold-tolerant shrubs, lichens, and herbaceous plants

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Increases in Rainfall Variability Affects Grassland Biomes

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Increases in Rainfall Variability Affects Grassland Biomes

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Increases in Rainfall Variability Affects Grassland Biomes

What factors influence the type and extent of prairies found in central North America?

Pattern occurs at different scales

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley How Predictable Are Communities? Frederick Clements promoted the view that biological communities are stable, integrated, and orderly entities with a highly predictable composition. Clements argued that communities develop by passing through a series of predictable stages dictated by extensive interactions among species, and that this development culminates in a stable final stage called a climax community. “All the stages which precede the climax are stages of growth.” ”As an organism the formation arises, grows, matures and dies.”

Old field Pioneering species Early successional community Mid-successional community Late-successional community Climax community Disturbance ends, site is invaded by short-lived weedy species. Weedy species replaced by longer-lived herbaceous species and grasses. Shrubs and short-lived trees begin to invade. Short-lived tree species mature; long- lived trees begin to invade. Long-lived tree species mature. Figure 50.11

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley How Predictable Are Communities? Henry Gleason, in contrast, contended that the community found in a particular area is neither stable nor predictable. According to Gleason, it is largely a matter of chance whether a similar community develops in the same area after a disturbance occurs. Which viewpoint is more accurate?

Whittaker’s studies of tree populations

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Identical Communities Do Not Develop in Identical Habitats

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Identical Communities Do Not Develop in Identical Habitats

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Identical Communities Do Not Develop in Identical Habitats

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Disturbance and Change in Ecological Communities Community composition and structure may change radically in response to changes in abiotic and biotic conditions. A disturbance is any event that removes some individuals or biomass from a community. The important feature of a disturbance is that it alters some aspect of resource availability.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Disturbance and Change in Ecological Communities The impact of disturbance is a function of three factors: (1) type of disturbance (2) frequency of disturbance (3) Severity of disturbance Most communities experience a characteristic type of disturbance, and in most cases, disturbances occur with a predictable frequency and severity. This is called a community's disturbance regime.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley History of Disturbance in a Fire-Prone Community Fire scars in the growth rings Fire scars Reconstructing history from fire scars

Community 1Community 2Community Species richness: Species diversity: A B C D E F Species Box 50.1, Figure 1 How do we measure diversity?

Simpson’s Index of Diversity Proportion of sample represented by species (p i ) Species A Species B Species C Species D Species E Community Community If you plug these numbers into the formula for Simpson’s Index, D = 5.00 for the community where all 5 species are at equal abundances (Row 3). In contrast, D = 2.81 for the community with the same 5 species at very unequal abundances (Row 4). As this example illustrates, Simpson’s index is more sensitive to changes in the abundant (rather than rare) species in a community. D = 1 /  (p i ) 2

Joseph Connell’s Intermediate Disturbance Hypothesis

Observational Evidence for IDH