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Disturbance

Disturbance. What are some examples of disturbances? Fire, hurricanes, insect outbreaks, volcanoes, floods, wind, drought… Definition

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Disturbance

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  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 2006Landcape 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. * * * * * Environmental data Biotic data * 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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