TitleMaximizing the effectiveness of grassland management for a grasshopper sparrow (Ammodramus savannarum) metapopulation
NameSeigel, Alison B. (author), Lockwood, Julie (chair), Lathrop, Richard (internal member), Jordan, Rebecca (internal member), Drake, David (outside member), Rutgers University, Graduate School - New Brunswick,
SubjectEcology and Evolution,
Grasshopper sparrow--Effect of habitat modification on,
DescriptionGrassland bird population declines have been attributed to habitat loss and fragmentation and the intensification of agricultural practices. Hayfields are being cut earlier and more frequently during the breeding season resulting in low reproductive success. Grassland bird conservation efforts generally focus on enrolling farmland into landowner incentive programs that require mowing to be delayed until after July 15. Delayed mowing improves grassland bird reproductive success by enabling breeding pairs to fledge at least one brood during the breeding season. This dissertation examines the effect of hayfield management on population viability of a grasshopper sparrow metapopulation in a fragmented landscape in New Jersey and uses statistical power analysis to assess the cost-effectiveness of grasshopper sparrow metapopulation monitoring programs.
I built a spatially-explicit, stage-structured, stochastic model of a grasshopper sparrow metapopulation to determine how probability of extinction (POE) is affected by: (1) total hayfield area enrolled, (2) size of enrolled hayfields, (3) number of hayfield patches enrolled, and (4) isolation of enrolled hayfields. I found that POE decreased quickly with increasing amounts of enrolled hayfield area. After 31 to 48% of hayfield area in the landscape was enrolled, POE decreased minimally with further enrollment. The number of grassland parcels enrolled was also negatively related to POE. When I incorporated a patch size effect (fecundity was directly related to hayfield size) into the model, POE increased within each enrollment category but still decreased with increasing amounts of enrolled grassland (Chapter 2). POE was directly related to the degree of isolation of enrolled hayfields.
Of the monitoring programs we evaluated, the most cost-effective program to detect a 7% population decline included 18 hayfields surveyed six times annually over five years. Additional survey effort would be necessary to detect a smaller population decline and to overcome observer variability in density estimates due to sampling error.
Hayfield management for grassland birds will be most effective when there is not only a focus on the amount of managed habitat, but also on local and landscape scale variables such as patch size and configuration. Cost-effective population monitoring is critical to evaluating the success of management decisions.
NoteIncludes bibliographical references
Noteby Alison B. Seigel
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.