Joseph R. Robb

Comparison of Three Burrowing Crayfish Capture Methods Based on Relationships with Species Morphology, Seasonality, and Habitat Quality

Abstract Three techniques used to capture burrowing crayfish were compared for efficiency and efficacy near Big Oaks National Wildlife Refuge. Excavation of burrows, Norrocky burrowing crayfish trap (NBCT), and burrowing crayfish mist nets (BCN) were simultaneously compared for capture efficiency and trap efficacy. Additional research goals were to evaluate patterns in capture rates with changes in seasonal activity, influence of burrow diameter size to capture success, relationships between differences in morphological characteristics of species and capture success, and capture success and habitat quality. Excavation caught significantly more burrowing crayfish than the other two methods (40.7%), but the NBCT (5.2%) was not significantly different from the BCN (4.5%) in trap efficiency. The relative percent efficacy success adjusted for effort of each method was 2.61% for the NBCT and 2.24% for the BCN. Positive correlations between habitat quality and increasing NBCT (rs = 0.414, P = 0.023) and increasing BCN (rs = 0.447, P = 0.013) trap efficiency success were found, while no significant linear relationship (rs = −0.134, P = 0.479) was observed between the Qualitative Habitat Evaluation Index score for habitat quality and excavation success. No significant correlation was observed between NBCT (rs = −0.273, P = 0.144) or BCN (rs = −0.286, P = 0.125) and annual date; however, a significant linear relationship was observed for excavation (rs = −0.372, P = 0.043) and annual date of collection. Individuals of Cambarus (Tubericambarus) polychromatus and Cambarus (Lacunicambarus) species “A” that were collected were significantly different in size; however, this was not a result of gear bias. A positive correlation was observed between C. polychromatus size and habitat quality indicating longer lived individuals occur in higher quality habitats.

Surveying a Threatened Amphibian Species through a Narrow Detection Window

Crawfish Frogs (Lithobates areolatus) are a relatively widespread but understudied North American species suspected to be in steep decline. Discussions to petition this species for federal listing have begun and therefore effective techniques to survey and monitor populations must be developed. Crawfish Frogs produce unusually loud breeding calls, making call surveys the most efficient way to assess populations; however, their peak breeding period lasts for only a few nights, sometimes for only one night. We used automated calling survey techniques at two wetlands where the numbers of Crawfish Frog males present were known (±1%) for the entire length of the breeding season to examine detection probabilities in relation to season, time of day, weather variables, survey duration, and the numbers of males present. We then used these data to ask three simple but important questions: 1) When should researchers listen—that is, what times and under what environmental conditions should surveys for Crawfish Frogs take place? 2) How long should surveys last? and 3) What can call surveys tell us about the size of a population? The most supported model for detection included the quadratic relationship of time and date, a positive linear relationship with temperature, and a negative linear relationship with recent rain, while the most supported model for estimating abundance included the quadratic relationship of time and date, and call rate. Five-minute surveys should suffice during peak breeding for known large populations; 15-minute surveys with repeat visits should be used for small populations or when sampling new areas. These findings should improve manually collected (auditory) call survey efficiencies for Crawfish Frogs, surveys that are being organized to provide the first objective data on the status of this species across its range.

Habitat Selection by Crawfish Frogs (Lithobates areolatus) in a Large Mixed Grassland/Forest Habitat

Abstract Our objective was to examine breeding dispersal, burrow-use characteristics, and burrow habitat selection by Crawfish Frogs (Lithobates areolatus) in two distinct vegetation types (open grasslands and a mosaic of forest and transitioning grasslands) in southeastern Indiana, from March to August 2009 and 2010. We captured 14 frogs at their breeding ponds and tracked them to their burrows using radio telemetry. Once we identified their burrows, we compared habitat metrics at the burrows to random locations. We used an information-theoretic model selection approach to approximate the parsimony of logistic regression models comparing the habitat features of burrows to random, available sites. Frogs dispersed a straight-line average distance of 215 m and used an average of four burrows. They generally did not change burrows after June. Our top model included covariates for the number of burrows, canopy cover, and a site covariate. Our results suggested that habitat selection by Crawfish Frogs occurred hierarchically; in mixed grassland/forest habitats, they first selected areas with low canopy cover, and then selected areas with many available burrows. To manage habitat for Crawfish Frogs, we recommend preventing woody encroachment and reducing canopy cover in grassland areas occupied by Crawfish Frogs. Additionally, areas with a large number of burrows appear to provide the most suitable Crawfish Frog habitat.

Fire and non‐native grass invasion interact to suppress tree regeneration in temperate deciduous forests

Summary 1. While many ecosystems depend on fire to maintain biodiversity, non-native plant invasions can enhance fire intensity, suppressing native species and generating a fire–invasion feedback. These dynamics have been observed in arid and semi-arid ecosystems, but fire–invasion interactions in temperate deciduous forests, where prescribed fires are often used as management tools to enhance native diversity, have rarely been investigated. 2. Here we evaluated the effects of a widespread invasive grass on fire behaviour in eastern deciduous forests in the USA and the potential effects of fire and invasions on tree regeneration. We planted native trees into invaded and uninvaded forests, quantified fuel loads, then applied landscape-scale prescribed fires and no-burn controls, and measured fire behaviour and tree seedling and invasive plant performance. 3. Our results show that fires in invaded habitats were significantly more intense, including higher fire temperatures, longer duration and higher flame heights, even though invasions did not alter total fuel loads. The invasion plus fire treatment suppressed native tree seedling survival by 54% compared to invasions without fire, and invasions reduced natural tree recruitment by 66%. 4. We also show that invasive plant biomass did not change from one season to the next in plots where fire was applied, but invader biomass declined significantly in unburned reference plots, suggesting a positive invasive grass–fire feedback. 5. Synthesis and applications. These findings demonstrate that fire–invasion interactions can have significant consequences for invaded temperate forest ecosystems by increasing fire intensity and reducing tree establishment while promoting invasive plant persistence. To encourage tree regeneration and slow invasive spread, we recommend that forest managers remove invasions prior to applying prescribed fires or avoid the use of fire in habitats invaded by non-native grasses.

Population and Conservation Genetics of Crawfish Frogs, Lithobates areolatus, at Their Northeastern Range Limit

Abstract Crawfish Frogs (Lithobates areolatus) are a North American ranid, considered near threatened globally with populations in decline throughout their range. We studied populations of Crawfish Frogs on local and regional scales at their northeastern range limit to (1) assess the level of genetic diversity within populations, (2) estimate fine-scale genetic structure, and (3) estimate genetic differentiation between populations at the regional level. We used 10 microsatellite loci to genotype frogs collected from three regional sites in Indiana separated by 50–172 km and at one of these sites within a network of three breeding ponds <1 km apart. Heterozygosity estimates revealed high levels of diversity within these populations (mean HO: 0.54–0.67 per site), which is encouraging for future management. The degree of population subdivision was low at the regional level (FST = 0.071 for sites within 172 km). Genetic differentiation was related to geographic distance between sampling sites, as predicted by an isolation-by-distance model. We observed no genetic differentiation between individuals sampled from ponds approximately 250 m apart and slight divergence of individuals from a pond approximately 750 m away. This suggests ponds within 1 km form a genetically distinct single breeding unit composed of multiple subpopulations. Finally, we observed high genetic differentiation between southwest and southeast Indiana sites indicating historical (rather than recent) isolation of these sites. These data will be applied to a regional management plan in an attempt to recover Crawfish Frogs along the northeastern extreme of their range.

Factors affecting nest survival of Henslow's Sparrows (Ammodramus henslowii) in southern Indiana

ABSTRACT Populations of Henslow’s Sparrows have declined dramatically in recent decades, coinciding with widespread loss of native grassland habitat. Prescribed burning is a primary tool for maintaining grassland patches, but its effects on nest survival of Henslow’s Sparrows remains largely unknown, especially in conjunction with other factors. We monitored 135 nests of Henslow’s Sparrows at Big Oaks National Wildlife Refuge in southern Indiana from 1998–2001 in an effort to understand factors influencing nest survival, including prescribed burning of habitat. We used a mixed-effects implementation of the logistic exposure model to predict daily nest survival in an information theoretic framework. We found that daily survival declined near the onset of hatching and increased with the height of standing dead vegetation, although this relationship was weak. We found only nominal support to suggest that time since burn influenced nest survival. Overall, nest age was the most important factor in estimating daily nest survival rates. Our daily survival estimate from our marginal model (0.937) was similar to that derived from the Mayfield method (0.944) suggesting that our results are comparable to previous studies using the Mayfield approach. Our results indicate that frequent burning to limit woody encroachment into grassland habitats might benefit Henslow’s Sparrow, but that a variety of factors ultimately influence daily nest survival. However, we note that burning too frequently can also limit occupancy by Henslow’s Sparrows. We suggest that additional research is needed to determine the population-level consequences of habitat alteration and if other extrinsic factors influence demographics of Henslow’s Sparrows.

Biological Diversity, Ecological Health and Condition of Aquatic Assemblages at National Wildlife Refuges in Southern Indiana, USA

Abstract The National Wildlife Refuge system is a vital resource for the protection and conservation of biodiversity and biological integrity in the United States. Surveys were conducted to determine the spatial and temporal patterns of fish, macroinvertebrate, and crayfish populations in two watersheds that encompass three refuges in southern Indiana. The Patoka River National Wildlife Refuge had the highest number of aquatic species with 355 macroinvertebrate taxa, six crayfish species, and 82 fish species, while the Big Oaks National Wildlife Refuge had 163 macroinvertebrate taxa, seven crayfish species, and 37 fish species. The Muscatatuck National Wildlife Refuge had the lowest diversity of macroinvertebrates with 96 taxa and six crayfish species, while possessing the second highest fish species richness with 51 species. Habitat quality was highest in the Muscatatuck River drainage with increased amounts of forested habitats compared to the Patoka River drainage. Biological integrity of the three refuges ranked the Patoka NWR as the lowest biological integrity (mean IBI reach scores = 35 IBI points), while Big Oaks had the highest biological integrity (mean IBI reach score = 41 IBI points). The Muscatatuck NWR had a mean IBI reach score of 31 during June, which seasonally increased to a mean of 40 IBI points during summer. Watershed IBI scores and habitat condition were highest in the Big Oaks NWR.