ch 21: Landscape Ecology: Structure, Processes, and Change

Landscape Ecology

Introduction to Landscape Ecology

Landscape ecology is a sub-discipline of ecology that examines how spatial variation in the landscape (structure) affects ecological processes (function). It focuses on the study of landscape structure, processes, and changes, integrating multiple ecosystems within a heterogeneous area.

• Landscape: A heterogeneous area composed of several ecosystems.

• Landscape Elements: Visually distinctive patches in an ecosystem, such as forests, ponds, or towns.

Example: A rural area with fields, forests, and rivers forms a landscape with multiple interacting ecosystems.

Large Scale Ecology

Overview of Large Scale Ecology

Large scale ecology encompasses landscape ecology, geographic ecology, and global ecology, each addressing ecological phenomena at increasing spatial scales.

• Landscape Ecology: Focuses on spatial variation and ecological processes within landscapes.

• Geographic Ecology: Studies patterns of plant and animal life that can be mapped, including biological diversity and species ranges.

• Global Ecology: Examines ecological phenomena and changes at a global scale, including human impacts on Earth.

Landscape Structure

Components of Landscape Structure

Landscape structure refers to the size, shape, composition, number, and position of ecosystems within a landscape. The arrangement of patches (e.g., woods, ponds, towns) forms a mosaic that defines landscape structure.

• Patch: A discrete area within a landscape, differing from its surroundings in composition or function.

• Mosaic: The pattern formed by the arrangement of patches.

Example: Forested and non-forested land patches in different regions can be quantified and compared to reveal landscape structure.

Quantifying Landscape Structure

Landscape structure can be analyzed by measuring patch area, shape, and distribution. These factors influence ecological processes and species interactions.

• Patch Area: Larger patches may support more species and individuals.

• Patch Shape: Circular patches have less edge per area than elongated patches, affecting edge effects and species movement.

Landscape	Forest Cover (%)	Patch Shape
Monroe	Low	Less circular
Somerset	High	More circular
Hudson	Medium	Medium
Boston	Low	Less circular
Washington	High	More circular

Additional info: Patch shape affects perimeter-to-area ratio, influencing edge effects and movement of species.

Landscape Processes

Influence of Structure on Processes

Landscape structure influences ecological processes such as the flow of energy, materials, and species between ecosystems within a landscape.

• Dispersal of Organisms: Movement of species between patches.

• Local Population Density: Number of individuals per unit area within a patch.

• Extinction of Local Populations: Loss of species from isolated patches.

• Lake Chemical Composition: Variation in water chemistry based on landscape position.

Landscape Structure and Dispersal

Dispersal of Small Mammals

Landscape structure can influence the movement of organisms between suitable habitats. Metapopulations are populations of species that occur in spatially isolated patches, with significant exchange of individuals.

• Metapopulation: A group of spatially separated populations of the same species, connected by migration.

• Example: Desert bighorn sheep in isolated mountain ranges of the southwestern U.S. and Northern Mexico.

Patch Size and Movement

Diffendorfer et al. studied how patch size affects movement of small mammals (rats, voles, mice). Animals move farther in fragmented landscapes to obtain resources and stay longer in isolated patches.

Patch Size	Mean Dispersal Distance	Proportion Remaining
Small	Low	Low
Medium	Medium	Medium
Large	High	High

Additional info: Fragmentation increases movement distance; isolation increases time spent in patches.

Butterfly Populations and Habitat Patch Size/Isolation

Hanski et al. found that butterfly density is significantly affected by the size and isolation of habitat patches in southwestern Finland.

• Population size within a patch increases with patch area.

• Population density decreases as patch area increases.

• Isolated patches have lower butterfly densities, partially maintained by immigration.

Habitat Corridors

Connecting habitat fragments with corridors of similar habitat can mitigate the effects of fragmentation. Haddad and Baum found that corridors increased movement of butterflies in early successional habitats.

Habitat Type	Butterfly Density
Connected patches	High
Isolated patches	Low

Landscape Position and Lake Chemistry

Effects of Landscape Position

Webster explored how the position of a lake in a landscape affects its chemical responses to drought. Lake position determines the proportion of water received as groundwater and the concentration of dissolved ions.

• Lakes at upper positions receive less groundwater, lower ion concentrations.

• Lakes at lower positions receive more groundwater, higher ion concentrations.

Lake Position	Groundwater Input	Dissolved Ions
Upper	Low	Low
Middle	Medium	Medium
Lower	High	High

Origins of Landscape Structure and Change

Geological Processes and Climate

Landscapes are structured and change in response to geological processes (volcanism, sedimentation, erosion) and climate (floods, droughts).

• Geological Processes: Volcanism creates new landforms; sedimentation and erosion reshape landscapes.

• Climate: Variation over time (e.g., floods) interacts with geological events to form landscape mosaics.

Organisms and Landscape Structure

Plants and animals can significantly influence landscape structure, sometimes acting as ecosystem engineers.

• Plants: Nitrogen-fixing legumes enrich soil, altering plant community structure.

• Animals: Keystone species such as elephants and beavers modify landscapes through their activities.

Example: Beavers build dams, create ponds, and alter hydrology, increasing wetlands and changing plant communities.

Effects of Beavers on Landscapes

• Increase extent of wetlands

• Change hydrologic regime (water flow)

• Trap sediments

• Increase patchiness of plant communities

• Reduce population size of preferred tree species

Johnston and Naiman documented that over 63 years, beaver-created area increased from 200 ha to 2,661 ha, transforming boreal forest into a complex mosaic.

Human Activities and Disturbance

Human activities and disturbances such as fire also play major roles in structuring and changing landscapes.

• Human Activities: Urbanization, agriculture, and resource extraction alter landscape structure.

• Disturbance: Events like fire can reset ecological succession and change landscape patterns.