GEOG20009 Lecture Notes - Lecture 5: Fractal Dimension, Measuring Instrument, Species Richness
15 May 2018
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Department
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Professor
LECTURE 5: HABITAT COMPLEXITY AND DIVERSITY
• RECAP: Limits to local diversity: dispersal constraints, environmental conditions at localities,
& new species unable to invade established community
ENVIRONMENTAL HETEROGENEITY
• Vague term, meaning variability in the environment
• Terrestrial ecologists: think about variety of
vegetation, and how this drives diversity
o Look at land cover, climate, soil
• How does variability translate into the number of
species in a locale?
• In this lecture, focus on vegetation + topography as
sources of heterogeneity
• There is a strong consistent relation between environmental heterogeneity & species
richness
o Higher heterogeneity = higher species richness
• Aquatic ecologists: environmental heterogeneity is also measurable in aquatic environments
o Higher heterogeneity = higher species richness
o Look at habitat complexity, diversity etc.
HABITAT COMPLEXITY
• Habitat Complexity: the coexistence of different kinds of elements that constitute a habitat
• Used by aquatic ecologists to infer heterogeneity
• Recognises 5 aspects: scales of habitat complexity, diversity of complexity-generating
elements, spatial arrangement of elements, sizes of elements and abundance/density of
elements
o So complex that it provides issue in measurement
FRACTAL DIMENSION
• As measuring scale decreases, total length increases – depends on size of measuring instrument
o There can be a consistent relation between length & measuring instrument
• Measuring fractal dimension is one way that can take account of some aspects of complexity
• Properties of landscapes can be scale-independent – look the same regardless of scale which you are examining
from (coastlines)
Effects of Physical Complexity
• Smaller animals walk further on complex surfaces
• Smaller animals can achieve higher densities on complex surfaces
• Complex environments gain higher species diversity than simple environments
• Plants have different complexities – affecting ability of fauna to move over them
• More complex the fractal dimension of an environment = higher range of species
THEORIES CONNECTING HABITAT COMPLEXITY & SPECIES DIVERSITY
• Physically complex habitats have different kinds of resources that provide for many diff species compared to simple
habitats
• New models: spatial scaling model, modern as compared to fractal experiments
o Requires that:
▪ Essential resources are patchy & distributed fractally
▪ Animals vary in their dispersal ability
o Data suggests this model may effectively connect habitat complexity &
species diversity
▪ Greater species diversity occurs in areas of a river where there are larger densities of
emergent rocks
Topics
• Environmental
heterogeneity & habitat
complexity
• Measuring these through
fractal dimension
• Examples of fractal
environments
• Fractal dimension &
diversity
Papers/Studies
• Tokeshi & Arikaki (2012)
• Jiang & Brandt (2016)
HIGHER HETEROGENEITY =
HIGHER SPECIES RICHNESS
(terrestrial & aquatic
environments)
Self-Similarity: an object which
is exactly like a part of itself
(Eg. fern fronds)
Species diversity is predictable
from dispersal ability and fractal
distributions of resources
Document Summary
Lecture 5: habitat complexity and diversity: recap: limits to local diversity: dispersal constraints, environmental conditions at localities, & new species unable to invade established community. Environmental heterogeneity: vague term, meaning variability in the environment. Terrestrial ecologists: think about variety of vegetation, and how this drives diversity. In this lecture, focus on vegetation + topography as sources of heterogeneity. There is a strong consistent relation between environmental heterogeneity & species richness: higher heterogeneity = higher species richness, aquatic ecologists: environmental heterogeneity is also measurable in aquatic environments, higher heterogeneity = higher species richness. So complex that it provides issue in measurement. Fractal dimension: as measuring scale decreases, total length increases depends on size of measuring instrument, there can be a consistent relation between length & measuring instrument. Environmental heterogeneity & habitat complexity: measuring these through fractal dimension.
