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Sampling scales define occupancy and underlying occupancy-abundance relationships in animals
Robin Steenweg1, Mark Hebblewhite1, Jesse Whittington2
1Wildlife Biology Program, W.A. Franke College of Forestry and Conservation, University of Montana, Missoula, Montana, 59812, USA.
Ecology
|October 25, 2017
Summary
Occupancy-abundance relationships are crucial for ecological studies. This research reveals how sampling scales influence occupancy estimates for mobile species, with point sampling proving robust across spatial grains but longer surveys impacting rare species.
Area of Science:
- Ecology and wildlife population monitoring
- Ecological modeling and spatial analysis
Background:
- Occupancy-abundance (OA) relationships are fundamental in ecology, yet studies often isolate occupancy and abundance data.
- Current occupancy models are increasingly used for population trends but may be affected by sampling design, especially for mobile species.
- Geographical closure assumptions are often violated in occupancy studies, potentially altering the relationship between occupancy and abundance.
Purpose of the Study:
- To develop a conceptual framework for understanding how sampling scales affect occupancy definitions and OA relationships for mobile organisms.
- To investigate the impact of spatial and temporal sampling scales, and sampling units (areal vs. point), on OA relationships.
- To test predictions using simulations and empirical data from remote camera surveys of mammals.
Main Methods:
- Conceptual framework development linking sampling scales to occupancy definition and OA relationships.
- Simulation studies to predict the effects of spatial grain, temporal duration, and sampling units on OA relationships.
- Empirical testing using remote camera data from 11 medium-large mammal species.
Main Results:
- Point sampling showed OA relationships unaffected by spatial sampling grain (cell size), unlike areal sampling.
- Temporal sampling duration increased the curvature of OA relationships; longer surveys inflated occupancy estimates, especially for rare species.
- Occupancy estimates for mobile species without geographical closure do not represent true occupancy.
Conclusions:
- Point-sampling surveys offer unbiased, simultaneous occupancy estimates for multiple species regardless of home-range size.
- Sampling scale (spatial grain and temporal duration) critically influences occupancy-abundance relationships and occupancy estimates.
- Future occupancy-based trend monitoring must clearly define sampling scales and their impact on OA relationships.
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