RESEARCH ARTICLE Low effective population size and survivorship in a grassland grouse C. L. Pruett • J. A. Johnson • L. C. Larsson • D. H. Wolfe • M. A. Patten Received: 9 August 2010 / Accepted: 26 April 2011 / Published online: 11 May 2011 Ó Springer Science+Business Media B.V. 2011 Abstract Assessments of census size (N c ) and effective population size (N e ) are necessary for the conservation of species exhibiting population declines. We examined two populations (Oklahoma and New Mexico) of the lesser prairie-chicken (Tympanuchus pallidicinctus), a declining lek-breeding bird, in which one population (Oklahoma) has larger clutch size and more nesting attempts per year but lower survival caused by human changes to the landscape. We estimated demographic and genetic estimates of N e for each population and found that both populations have low N e estimates with a risk of inbreeding depression. Although Oklahoma females produce a larger number of offspring, the proportion of females successfully reproducing is not higher than in New Mexico. Higher reproductive effort has likely reached a physiological limit in Oklahoma prairie- chickens but has not led to a higher N e or even a larger N c than New Mexico. We propose that future conservation efforts focus on maximizing survivorship and decreasing the variance in reproductive success because these factors are more likely than increasing reproductive output alone to yield population persistence in lek-breeding species. Keywords Lek  Lesser prairie-chicken  Microsatellite loci  Mitochondrial DNA  Tympanuchus pallidicinctus Introduction Identifying the factors contributing to population decline and extinction are crucial for the conservation of wildlife. Wildlife managers primarily assess the health of popula- tions based on census size (N c ); however, estimates of effective population size (N e ) are arguably more informa- tive for determining the extinction risk of small populations because this measure reflects the actual number of breeders in the population (Traill et al. 2010). Populations with small effective population sizes are greatly affected by genetic drift and loss of adaptive potential and they have an increased risk of inbreeding depression (Keller and Waller 2002; Frankham 2005). For example in populations with small N e , deleterious alleles (which would be selected against in large populations) may behave as if they are neutral and are more likely to become fixed compared to populations with much larger N e (Ellegren 2009). Thus, estimates of N e are necessary for populations that are of conservation concern, so that managers can properly weigh extinction risks resulting from demographic and genetic factors. In virtually all populations, N e is smaller than the N c because of deviations from a Wright–Fisher ideal popula- tion (N e /N c = 1). These deviations include differences in demographic factors such as fluctuations in population size and survivorship and differences in mating systems and variance in reproductive success (Frankham et al. 2002). C. L. Pruett  L. C. Larsson  D. H. Wolfe  M. A. Patten Sutton Avian Research Center, University of Oklahoma, Bartlesville, OK, USA C. L. Pruett (&) Department of Biological Sciences, Florida Institute of Technology, Melbourne, FL 32901, USA e-mail: cpruett@fit.edu J. A. Johnson Department of Biological Sciences and Institute of Applied Sciences, University of North Texas, Denton, TX, USA M. A. Patten Oklahoma Biological Survey and Department of Zoology, University of Oklahoma, Norman, OK, USA 123 Conserv Genet (2011) 12:1205–1214 DOI 10.1007/s10592-011-0223-z