Source/Sink Dynamics Project
Endangered butterflies as a model system for managing source-sink dynamics on Department of Defense lands
Elizabeth Crone (Harvard Forest)
William Morris (Duke University)
Cheryl Schultz (Washington State University)
Nick Haddad (North Carolina State University)
Brian Hudgens (Institute for Wildlife Studies)
Christine Damiani (Institute for Wildlife Studies)
IWS research ecologists have taken part in a study of source-sink dynamics (described below) on Department of Defense (DoD) lands with support from the Strategic Environmental Research and Development Program (SERDP).
Background
DoD lands provide the best available habitat for numerous threatened, endangered and at-risk (TER-S) species. Many of these species do best on DoD lands because they require disturbance-dependent habitats such as those created by fires and localized floods, and DoD resource managers can manage these disturbances with techniques that are difficult or impossible to employ on private lands. Restoration of habitat is another technique that may improve conditions for these species. Ideally, such management creates population sources (where births exceed deaths) that increase metapopulation viability. However, habitat management often has both beneficial and detrimental effects on populations of TER-S species. For example, where fires are necessary in grasslands to control woody plants and improve habitat quality for wildlife, those fires often kill animals, particularly less mobile juveniles. In this case, too-frequent management runs the risk of creating sinks (where deaths exceed births) rather than sources. Additionally, restoration and management have the potential to create ecological traps - habitat that animals perceive as high-quality, but acts as a population sink. Our work focuses on temporal change in habitat quality following management or restoration that may lead local habitat patches to cycle from sink to source status and back.
Objective
Through a combination of field studies and state-of-the-art quantitative models, we are comparing the effects of management on source-sink dynamics of three focal species, representing a continuum from extraordinarily well studied to relatively unknown, and a continuum of management strategies from regular, periodic management to de novo habitat creation. Butterflies have numerous advantages as models for source-sink dynamics, including rapid generation times and relatively limited dispersal, but they are subject to the same processes that determine source-sink dynamics of longer-lived, more vagile taxa.
Brian Hudgens of IWS searches for larvae.
Team searches for Fender's blue larvae
Species Studies
For all 3 species, we collect data on both demography and movement behaviors at all phases of the disturbance cycle that follows management or restoration.
Fender’s blue butterfly (Icaricia icarioides fenderi)
Evaluate source-sink dynamics in relation to controlled burning, and assess whether past restoration by direct planting could have created an ecological trap in an adjacent remnant population.
St. Francis satyr (Neonympha mitchellii francisci)
Test effects of patch isolation on population dynamics following two forms of habitat restoration: removal of hardwoods from late-successional wetlands, and wetland creation by controlled inundation.
Taylor’s checkerspot (Euphydryas editha taylori)
Assess whether herbicide and mowing, which are used to control invasion of native prairie by nonnative grasses and shrubs, are sufficient to convert sink to source habitat.
Simulation Models
IWS researchers use the collected data to parameterize dynamic source-sink models for each species, and will validate the models by testing whether they can reproduce the consequences of ongoing management. If fully-parameterized models are sufficient to explain past responses to restoration, we use them to test which features of demography and behavior are most important in determining population responses. In an attempt to find the simplest effective model, we then compare predictions that include only subsets of demographic and behavioral responses.
Christine Damiani of IWS samples vegetation
Representative butterfly species managed on military lands (focal species in the present study are in bold)
Smith’s blue
Status: Endangered
Location: Ft. Ord (CA)
Oregon silverspot
Status: Threatened
Location: Camp Rilea (OR)
Mardon skipper
Status: Candidate
Location: Fort Lewis (WA)
Crystal skipper
Status: Federal Species of Concern
Location: Possibly Camp LeJeune (NC)
Puget blue
State-listed
Location: Fort Lewis (WA)
Carson wandering skipper
Status: Endangered
Location: Sierra Army Depot (CA)
Fender’s blue
Status: Endangered
Location: Camp Adair & USACE Fern Ridge (OR)
Karner blue
Status: Endangered
Location: Fort McCoy (WI)
Quino checkerspot
Status: Endangered
Location: Camp Pendleton (CA)
St. Francis satyr
Status: Endangered
Location: Ft. Bragg (NC)
Benefits
With the validated models, we are collaborating directly with managers of our focal species to assess which management strategies have the greatest chance of improving metapopulation viability at the lowest cost. We can determine strategies such as appropriate return intervals of managed disturbances (fires and inundation), and the best locations to create new habitat patches and to augment or reintroduce populations.
Transition
We are creating statistical and spatial modeling tools that can be used to assess source-sink consequences of management for other TER-S species on DoD lands. We apply these tools to existing data for other, non-focal species (both butterflies and vertebrates), and assess the extent to which available data inform management of spatial populations in dynamic source-sink landscapes.
The team working on this project, including IWS researchers, has decades of experience working with TER-S butterflies and other taxa, and are leaders in measuring and modeling demography and behavior, as well as decision analysis. Our results will guide management of TER-S species on restored military lands to create sources and promote species recovery.