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Disturbance

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Bossenbroek, Wagner & Wiens 2006 Landcape Ecology ... Landscape Ecology. Hierarchical variance partitioning. Geographic. Space. Environmental ... – PowerPoint PPT presentation

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Title: Disturbance


1
Disturbance
  • What are some examples of disturbances?
  • Fire, hurricanes, insect outbreaks, volcanoes,
    floods, wind, drought
  • Definition
  • Disturbances are relatively discrete events in
    time that disrupt ecosystem, community or
    population structure and change resources,
    substrate availability or the physical
    environment.

2
Intermediate disturbance hypothesis.
3
Factors of Disturbance
  • Frequency
  • Severity

4
One Example Using Phytoplankton
5
Ph.D. research
Objective to determine the spatial structure of
biotic communities and how these patterns of
community composition change across a major
environmental gradient.
6
Taxon-dependent scaling beetles, birds and
vegetation at four North American grassland sites.
  • (1) What scale of environmental variables
    explains the most variance in community structure
    for beetles, birds and plants?
  • (2) Do these relationships change in a systematic
    way across a regional gradient?

Bossenbroek, Wagner Wiens 2006 Landcape Ecology
7
Study Sites
Pawnee National Grassland
Smoky Valley Ranch
Denver
Topeka
Fox Ranch
Konza Prairie
Location of the four sites sampled from
north-central Colorado to central Kansas.
8
Study Design
2 km
1m Soil sample (pH, texture) Temperature loggers
(hourly)
Beetle pitfall traps (3 days in June)
Vascular plant quadrat 1m2 (June, Aug)
Vegetation structure 5m cover for cacti and
shrub species 30m distance to nearest
medium/large shrub
Bird sightings along 50m segments (June)
Digital orthophotos (1m resolution) 2 landsat
scenes (30 m resolution)
9
General Results Species Number
10
Predictions
(1) What scale of environmental variables
explains the most variance in community structure
for beetles, birds and plants?
Scale of explanatory variables
Trap Local Landscape
Plants Beetles
Birds
Mobility
11
Predictions
(2) Do these relationships change in a
systematic way across a regional gradient?
Scale of explanatory variables
Trap Local Landscape
West
East
Heterogeneity
12
Canonical Correspondence Analysis
  • Ordination technique
  • Canonical Analysis
  • Reduces dimensionality of community structure.
  • Canonical Correspondence Analysis
  • Determines the environmental factors that are
    related to community structure.

13
Ordination
  • Logical means of ordering communities according
    to environmental parameters

14
Hierarchical variance partitioning
Variance
Communities
Cushman McGarigal 2003. Landscape Ecology
15
Hierarchical variance partitioning
Geographic Space
Environmental Variables
16
Hierarchical variance partitioning
Environmental Variables
Geographic Space
Trap
Landscape
Local
17
Total variance explained by environmental
variables and geographic space.
Variance Explained
Transect
East
West
18
Hierarchical variance partitioning
19
West
Homogeneous
Heterogeneous
East
20
Results
(1) What scale of environmental variables
explains the most variance in community structure
for beetles, birds and plants?
Scale of explanatory variables
Trap Local Landscape
Plants Beetles
Birds
Mobility
21
Results
(2) Do these relationships change in a
systematic way across a regional gradient? - NO!
Scale of explanatory variables
Trap Local Landscape
West
East
Heterogeneity
22
Conclusions
  • Regional differences are important.
  • Similarities between taxonomic groups do not
    always hold across a region.
  • Indicator taxa?
  • Multiple scales important for range of taxonomic
    groups.
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