Download Edge effects

Introduction – Landscape Ecology
• Landscape Ecology: Study of landscape
structure and processes.
– Landscape: Heterogeneous area composed of
several ecosystems.
– Landscape Elements: Visually distinctive
patches in an ecosystem.
Human Land Use Practices
Ecosystem simplification:
Intensive Agriculture
&
Clean Farming
Timber Extraction
&
Fragmentation
Roads: Formation of Barriers in Landscapes
Formation of
Terrestrial “Islands”
Habitat Fragmentation
• Process of breaking contiguous unit into
smaller pieces; area & distance
components
• Leads to:
• Community & Ecosystem processes
altered
#patches
Patch isolation
Patch size
Edge
Habitat Fragmentation
• area-sensitive species: species that
require minimum patch size for daily
life requirements
• Edge effects: influence of factors from
outside of a patch
Increased Edge Habitat
Increased Edge Habitat
Edge Effects
• Habitat surrounding a patch can:
- change abiotic conditions; e.g., temp.
- change biotic interactions, e.g.,
predation
Example of nest predation = edge effect of
approximately 50 m into forest patch
Habitat Fragmentation
• First-Order Effects: fragmentation leads
to change in a species’ abundance and/or
distribution
Habitat Fragmentation
• Higher-Order Effects: fragmentation
indirectly leads to change in a species
abundance and/or distribution via altered
species interactions
Habitat Fragmentation: SpeciesSpecific Sensitivity?
• Rare species = more vulnerable
• Wide ranging species = large-area
requirements
• Species with reduced mobility = more
vulnerable
• Species with low fecundity (related to
rarity?)
• Species with short life cycle (or multistage life cycle?)
Habitat Fragmentation: SpeciesSpecific Sensitivity?
• Interior-dependent species
• Species vulnerable to human exploitation
or disturbance
• Specialist species?
Implications of Changes in Scale
Insects sampled at 10-m intervals for 100 m
45
40
35
30
25
Predator
Prey
20
15
Pr
ey
Pr
ed
at
or
10
5
0
Implications of Changes in Scale
Insects sampled at 2000-m intervals for 20,000 m
45
40
35
30
25
Predator
Prey
20
15
Pr
ey
Pr
ed
at
or
10
5
0
Landscape Processes
• Landscape structure influences processes
such as the flow of energy, materials, and
species between the ecosystem within a
landscape.
Landscape Structure and
Dispersal of Small Mammals
Habitat Patch Size and Isolation
and Density of Butterfly
Populations
Introduction – Geographical Ecology
• MacArthur defined geographical ecology as
search for patterns of plant and animal life
that can be put on a map.
– Above level of landscape ecology
Island Area and Species Richness
Species-Area Relationship
Island Biogeography
• equilibrium model suggesting number of
species occurring on an island represents
a balance between immigration (in) and
extinction (out)
• Robert MacArthur & E.O. Wilson
Equilibrium Model of Island
Biogeography
• Proposed rates of extinction on islands would be
determined mainly by island size.
– LG near islands will support highest number.
– SM far islands will support lowest number.
– SM near and LG far will support intermediate number.