Chapter 22 conceptsLandscape ecology examines ecological patterns and processes at large spatial scales.The number of species increases with area.On a global scale, biodiversity is highest near the equator and declines toward the poles.The distribution of species around the world is affected by Earth’s history.1245The equilibrium theory of island biogeography incorporates both area and isolation.3
Habitat heterogeneity1Landscape ecology: the field of study that considers the spatial arrangement of habitats at different scales and examines how they influence individuals, populations, communities, and ecosystems.Current habitat heterogeneity is a reflection of recent and historical events caused by natural and human forces.Legacy effects: a long-lasting influence of historical processes on the current ecology of an area.Example:Eskers are the remnants of streams of water that flowed inside glaciers; as the streams flowed, they deposited soil and rock on the streambed.After the glaciers melted, the streams appeared as long, winding hills.
Habitat heterogeneity1Natural forces (e.g., tornadoes, hurricanes, floods, mudslides, fires) continue to cause habitat heterogeneity.Human activity has influenced the intensity, frequency, and ecological influence of natural forces.Example:Throughout the twentieth century, natural fires were suppressed in Yellowstone National Park.In 1988, hundreds of fires were ignited by human activity and natural forces (e.g., lightning).Patterns of burning depended on landscape characteristics (e.g., amount of plant litter, wind patterns).
Habitat heterogeneity1Humans act as ecosystem engineers by constructing buildings, dams, irrigation channels, etc.Human activity causes habitat heterogeneity.Example:Villages and farms built by the Romans were abandoned by the fourth century CE.Ancient building materials broke down and contributed minerals to the soil; introduced crop species remained in the landscape.Recently, researchers found that sites closer to settlements had high soil pH, more phosphorus, and greater species richness.
Habitat heterogeneity and diversity1Species richness often increases from the local to landscape scale because habitat diversity increases along this gradient.Local (i.e., alpha) diversity: the number of species in a relatively small area of homogenous habitat, such as a stream.Regional (i.e., gamma) diversity: the number of species in all of the habitats that comprise a large geographic area.Example:In a survey of birds along 27 streams in Vermont, researchers found that each stream supported ~17 species (i.e., alpha diversity), whereas the combination of streams supported 101 species (i.e., gamma diversity).