Resource selection by the eastern massasauga rattlesnake on managed land in southwestern Michigan

The eastern massasauga rattlesnake (Sistrurus catenatus catenatus) has experienced population declines throughout its range and is now a candidate for federal protection. However, little is known about massasauga habitat selection in Michigan, particularly in actively managed landscapes. Our objectives were to: 1) quantify whether massasaugas in southwestern Michigan select certain vegetation types disproportionately to their availability and 2) quantify whether the vegetation structure associated with snake locations differed between managed (e.g., burning, woody species removal) and unmanaged stands. We implanted radio transmitters in 51 snakes from 2004 to 2005 and 2008 to 2009. We quantified second-order resource selection using compositional analysis, and modeled the effect of habitat management efforts on vegetation using 4 structural variables. All snakes selected cover types disproportionately to their availability (P = 0.001); a ranking matrix ordered the vegetation types, from most to least used, as: early-mid successional deciduous wetland > early-mid successional deciduous upland > developed > late successional mixed lowland forest > late successional deciduous upland forest. We found that snakes in managed areas were associated with greater amounts of dead herbaceous cover (P = 0.005) and less woody stem density (P < 0.001) and tree dominance (P < 0.001) than were snakes in unmanaged areas; however, live herbaceous cover was comparable. Our results can be used by regional managers to provide early and mid successional habitat with structure similar to that selected by snakes in Michigan. © 2011 The Wildlife Society.     

Similarity of contemporary and historical gene flow among highly fragmented populations of an endangered rattlesnake

Populations of endangered taxa in recently fragmented habitats often show high levels of genetic structure, but the role that contemporary versus historical processes play in generating this pattern is unclear. The eastern massasauga rattlesnake (Sistrurus c. catenatus) is an endangered snake that presently occurs throughout central and eastern North America in a series of populations that are isolated because of habitat fragmentation and destruction. Here, we use data from 19 species-specific microsatellite DNA loci to assess the levels of genetic differentiation, genetic effective population size, and contemporary and historical levels of gene flow for 19 populations sampled across the range of this snake. Eastern massasaugas display high levels of genetic differentiation (overall θ(Fst) = 0.21) and a Bayesian clustering method indicates that each population represents a unique genetic cluster even at regional spatial scales. There is a twofold variation in genetically effective population sizes but little genetic evidence that populations have undergone recent or historical declines in size. Finally, both contemporary and historical migration rates among populations were low and similar in magnitude even for populations located <7 km apart. A test of alternate models of population history strongly favours a model of long-term drift-migration equilibrium over a recent isolation drift-only model. These results suggest that recent habitat fragmentation has had little effect on the genetic characteristics of these snakes, but rather that this species has historically existed in small isolated populations that may be resistant to the long-term negative effects of inbreeding.     

Evaluating Basking-Habitat Deficiency in the Threatened Eastern Massasauga Rattlesnake

ABSTRACT Woody plant succession is hypothesized to threaten many reptile populations by reducing the amount of solar energy available for thermoregulation. Mitigation via vegetation management is often recommended; however, the need for such management practices rarely has been evaluated. We examined the need for basking-site enhancement for the eastern massasauga rattlesnake (Sistrurus c. catenatus; hereafter EMR) in New York, USA, where only 2 populations remain: one at an open-canopy site and another at a closed-canopy site. Microhabitat temperatures were substantially lower at the closed-canopy site, where EMRs selected the warmest available basking sites. Eastern massasauga rattlesnakes in the open-canopy population selected basking sites that afforded greater cryptic cover. We recommend experimental reduction of shrub cover to improve EMR basking habitat at the closed-canopy site. More generally, we caution that management efforts to reduce shrub cover for basking EMRs should maintain adequate cryptic cover.     

Historical versus contemporary migration in fragmented populations

Separating historical effects from recent anthropogenic pressures on population structure is paramount for understanding how species have persisted over time and how conservation efforts should best proceed. In this issue of Molecular Ecology, Chiucchi & Gibbs (2010) have separated the impacts of ancient and modern habitat fragmentation on genetic structure and migration rates in an endangered species of rattlesnake, the eastern massasauga (Sistrurus catenatus). Previous studies have ignored ancient processes, estimated genetic isolation and migration using collections from different timescales, used markers with different rates of evolution or compared contemporary populations in both continuous and fragmented habitats (Keyghobadi 2007). Here, Chiucchi & Gibbs (2010) estimate migration parameters from microsatellites at two timescales using coalescent methods. Results strongly suggest that massasaugas are characterized by the low levels of migration with strong regional and range-wide differences, typical of many organisms residing in the patches of habitat surrounded by seas of agriculture, but that these patterns have existed since the Pleistocene. The novel methodology and hypotheses addressed in Chiucchi & Gibbs (2010) highlight future avenues for examining the impacts of fragmentation through time.     

Range-wide analysis of eastern massasauga survivorship

Decisions affecting wildlife management and conservation policy of imperiled species are often aided by population models. Reliable population models require accurate estimates of vital rates and an understanding of how vital rates vary geographically. The eastern massasauga (Sistrurus catenatus catenatus) is a rattlesnake species found in the Great Lakes region of North America. Populations of the eastern massasauga are fragmented and only a few areas harbor multiple, sizable populations. Eastern massasauga research has typically focused on single populations or local metapopulations but results suggest that demographic parameters vary geographically. We used 21 radiotelemetry datasets comprising 499 telemetered snakes from 16 distinct locations throughout the range of the eastern massasauga to characterize geographic patterns of adult survival using the known-fate model in Program MARK. Annual adult survival ranged from 0.35 to 0.95 (mean = 0.67) and increased along a southwest to northeast geographic axis. Further analysis of 6 datasets indicated no consistent difference in survival between males and females. Our results provide a better understanding of the relationship between survivorship and geography for the eastern massasauga and suggest that such variation should be incorporated into population models as well as local and regional management plans. © 2012 The Wildlife Society.     

Genetic identity of endangered massasauga rattlesnakes (Sistrurus sp.) in Missouri

An important application of DNA-based genetic techniques in conservation genetics is to establish the taxonomic identity of individuals whose ancestry is uncertain, especially those from declining populations. Massasauga rattlesnakes (Sistrurus catenatus) in Missouri currently persist in three isolated populations and have been classified as eastern massasauga rattlesnakes (S. c. catenatus), which is a candidate for listing as a Federally Threatened or Endangered species. However, previous morphological evidence has suggested that these snakes are either hybrids between the eastern massasauga (S. c. catenatus) and the non-threatened western massasauga (S. c. tergeminus) or are pure S. c. tergeminus. Here, we analyze microsatellite DNA and mtDNA variation to assess the taxonomic identity of individuals from two of the three populations specifically those found in Holt and Linn Counties, Missouri. Population and phylogenetic analyses strongly support the conclusion that snakes in both populations are genetically most similar to reference S. c. tergeminus individuals from Kansas and are not related to S. c. catenatus individuals from Illinois and Ohio. These results argue that the current classification of these snakes as endangered S. c. catenatus is unwarranted and hence that the overall range-wide numbers of S. c. catenatus are less than previously estimated. Nonetheless the Missouri populations, while not part of the federally listed taxon, are strongly deserving of protected status at the state level because of their rarity within the state.     

Individual‐based ecology of coastal birds

Conservation objectives for non‐breeding coastal birds (shorebirds and wildfowl) are determined from their population size at coastal sites. To advise coastal managers, models must predict quantitatively the effects of environmental change on population size or the demographic rates (mortality and reproduction) that determine it. As habitat association models and depletion models are not able to do this, we developed an approach that has produced such predictions thereby enabling policy makers to make evidence‐based decisions. Our conceptual framework is individual‐based ecology, in which populations are viewed as having properties (e.g. size) that arise from the traits (e.g. behaviour, physiology) and interactions of their constituent individuals. The link between individuals and populations is made through individual‐based models (IBMs) that follow the fitness‐maximising decisions of individuals and predict population‐level consequences (e.g. mortality rate) from the fates of these individuals. Our first IBM was for oystercatchers Haematopus ostralegus and accurately predicted their density‐dependent mortality. Subsequently, IBMs were developed for several shorebird and wildfowl species at several European sites, and were shown to predict accurately overwinter mortality, and the foraging behaviour from which predictions are derived. They have been used to predict the effect on survival in coastal birds of sea level rise, habitat loss, wind farm development, shellfishing and human disturbance. This review emphasises the wider applicability of the approach, and identifies other systems to which it could be applied. We view the IBM approach as a very useful contribution to the general problem of how to advance ecology to the point where we can routinely make meaningful predictions of how populations respond to environmental change.     

Piping plover habitat selection and nest success on natural,managed, and engineered sandbars

Loss of breeding habitat and nest predation have contributed to the decline of many shorebird species. The United States Army Corps of Engineers (USACE) initiated a piping plover (Charadrius melodus) habitat creation and augmentation program on the Missouri River in the summer of 2004. The USACE increased unvegetated sandbar habitat by depositing dredged material (engineered sandbars) and by clearing vegetation from existing sandbars (managed sandbars). We evaluated the effects of this increase in nesting and foraging habitat on habitat selection and nest daily survival rate (DSR) of piping plovers on Lewis and Clark Lake and the Gavins Point Reach of the Missouri River from 2005 to 2007 (n = 623 nests). Piping plovers selected engineered sandbars more often than expected based on area and selected natural and managed habitats less than expected based on area. Daily survival rate on engineered sandbars was significantly higher than on natural or managed sandbars (log odds: 2.50, 95% CI: 1.05–5.94). Thus, plovers' habitat selection may have increased their nesting success. Our results suggest that habitat augmentation may stave off declines in piping plover populations limited by insufficient habitat and low nesting success. © 2011 The Wildlife Society.     

To forage,mate, or thermoregulate: Influence of resource manipulation on male rattlesnake behavior

Male animals should preferentially allocate their time to performing activities that promote enhancing reproductive opportunity, but the need to acquire resources for growth and survival may compete with those behaviors in the short term. Thus, behaviors which require differing movement patterns such as ambushing prey and actively searching for mates can be mutually exclusive. Consequently, males that succeed at foraging could invest greater time and energy into mate searching. We radio‐tracked sixteen male massasauga rattlesnakes (Sistrurus catenatus) and supplemented the diets of half the snakes with mice across an active season. We tested the predictions that reduced foraging needs would allow fed snakes to move (i.e., mate search) more, but that they would consequently be stationary to thermoregulate less, than unfed controls. Contrary to our first prediction, we found no evidence that fed snakes altered their mate searching behavior compared to controls. However, we found controls maintained higher body temperatures than fed snakes during the breeding season, perhaps because fed snakes spent less time in exposed ambush sites. Fed snakes had higher body condition scores than controls when the breeding season ended. Our results suggest the potential costs incurred by devoting time to stationary foraging may be outweighed by the drive to increase mating opportunities. Such instances may be especially valuable for massasaugas and other temperate reptiles that can remain inactive for upwards of half their lives or longer in some cases, and for female rattlesnakes that generally exhibit biennial or more protracted reproductive cycles.     

Landscape-Level Assessment of Brood Rearing Habitat for Greater Sage-Grouse in Nevada

Abstract: Loss of quality brood rearing habitat, resulting in reduced chick growth and poor recruitment, is one mechanism associated with decline of greater sage-grouse (Centrocercus urophasianus) populations. Low chick survival rates are typically attributed to poor-quality brood rearing habitat. Models that delineate suitability of sage-grouse nesting or brood rearing habitat at the landscape scale can provide key insights into the relationship between sage-grouse and the environment, allowing managers to identify and prioritize habitats for protection or restoration. We used Southwest Regional Gap landcover types to identify early and late greater sage-grouse brood rearing in east-central Nevada. We conducted an Ecological Niche Factor Analysis to 1) examine the effect these landcover types and other ecogeographical variables have on sage-grouse selection of brood rearing habitat, and 2) generate landscape-scale suitability maps. We also evaluated if incorporating a fitness component (brood survival) in landscape spatial analyses of habitat quality influenced our assessment of habitat suitability. Because 36% of our 6,500-km² study area was identified as early brood rearing habitat, we believe this habitat may not be limiting greater sage-grouse populations in east-central Nevada, USA, at least in wet years. We found strong selection for particular landcover types (e.g., higher elevation, moist sites with riparian shrubs or montane sagebrush) during late brood rearing. Late brood rearing habitat on which broods were successfully reared represented only 2.8% of the study area and had a restricted distribution, suggesting the potential that such habitat could limit sage-grouse populations in east-central Nevada.     

Selection of nest-site habitat by interior least terns in relation to sandbar construction

Federally endangered interior least terns (Sternula antillarum) nest on bare or sparsely vegetated sandbars on midcontinent river systems. Loss of nesting habitat has been implicated as a cause of population declines, and managing these habitats is a major initiative in population recovery. One such initiative involves construction of mid-channel sandbars on the Missouri River, where natural sandbar habitat has declined in quantity and quality since the late 1990s. We evaluated nest-site habitat selection by least terns on constructed and natural sandbars by comparing vegetation, substrate, and debris variables at nest sites (n = 798) and random points (n = 1,113) in bare or sparsely vegetated habitats. Our logistic regression models revealed that a broader suite of habitat features was important in nest-site selection on constructed than on natural sandbars. Odds ratios for habitat variables indicated that avoidance of habitat features was the dominant nest-site selection process on both sandbar types, with nesting terns being attracted to nest-site habitat features (gravel and debris) and avoiding vegetation only on constructed sandbars, and avoiding silt and leaf litter on both sandbar types. Despite the seemingly uniform nature of these habitats, our results suggest that a complex suite of habitat features influences nest-site choice by least terns. However, nest-site selection in this social, colonially nesting species may be influenced by other factors, including spatial arrangement of bare sand habitat, proximity to other least terns, and prior habitat occupancy by piping plovers (Charadrius melodus). We found that nest-site selection was sensitive to subtle variation in habitat features, suggesting that rigor in maintaining habitat condition will be necessary in managing sandbars for the benefit of least terns. Further, management strategies that reduce habitat features that are avoided by least terns may be the most beneficial to nesting least terns. © 2011 The Wildlife Society.     

Genetic variation in field and laboratory populations of the spined soldier bug,Podisus maculiventris

The predatory spined soldier bug, Podisus maculiventris (Say) (Heteroptera: Pentatomidae), is an economically important and highly valued biological control agent. There is substantial information on the biology, ecology, behavior, and rearing of this stink bug. However, virtually nothing is known of its genetic variation, in natural or domesticated populations. To address this lacuna, we used amplified fragment length polymorphism (AFLP) to assess the genetic variability of field and laboratory populations. Four AFLP universal primer combinations yielded a total of 209 usable loci. The AFLP results showed greater genetic variability between populations from Missouri and Mississippi (both USA), and relatively low variability within Missouri populations. We infer little genetic isolation among Missouri field populations and within laboratory populations, but a significant genetic isolation between Missouri and Mississippi populations.     

Spatial patterns of the frog Oophaga pumilio in a plantation system are consistent with conspecific attraction

The conspecific attraction hypothesis predicts that individuals are attracted to conspecifics because conspecifics may be cues to quality habitat and/or colonists may benefit from living in aggregations. Poison frogs (Dendrobatidae) are aposematic, territorial, and visually oriented—three characteristics which make dendrobatids an appropriate model to test for conspecific attraction. In this study, we tested this hypothesis using an extensive mark‐recapture dataset of the strawberry poison frog (Oophaga pumilio) from La Selva Biological Station, Costa Rica. Data were collected from replicate populations in a relatively homogenous Theobroma cacao plantation, which provided a unique opportunity to test how conspecifics influence the spatial ecology of migrants in a controlled habitat with homogenous structure. We predicted that (1) individuals entering a population would aggregate with resident adults, (2) migrants would share sites with residents at a greater frequency than expected by chance, and (3) migrant home ranges would have shorter nearest‐neighbor distances (NND) to residents than expected by chance. The results were consistent with these three predictions: Relative to random simulations, we observed significant aggregation, home‐range overlap, and NND distribution functions in four, five, and six, respectively, of the six migrant–resident groups analyzed. Conspecific attraction may benefit migrant O. pumilio by providing cues to suitable home sites and/or increasing the potential for social interactions with conspecifics; if true, these benefits should outweigh the negative effects of other factors associated with aggregation. The observed aggregation between migrant and resident O. pumilio is consistent with conspecific attraction in dendrobatid frogs, and our study provides rare support from a field setting that conspecific attraction may be a relevant mechanism for models of anuran spatial ecology.     

Genetic structure of populations of the threatened eastern massasauga rattlesnake, Sistrurus c. catenatus: evidence from microsatellite DNA markers

Throughout its distribution in North America, the threatened eastern massasauga rattlesnake ( Sistrurus c. catenatus ) persists in a series of habitat-isolated disjunct populations of varying size. Here, we use six microsatellite DNA loci to generate information on the degree of genetic differentiation between, and the levels of inbreeding within populations to understand how evolutionary processes operate in these populations and aid the development of conservation plans for this species. Samples were collected from 199 individuals from five populations in Ontario, New York and Ohio. Our results show that all sampled populations: (i) differ significantly in allele frequencies even though some populations are < 50 km apart, and may contain genetically distinct subpopulations < 2 km apart; (ii) have an average of 23% of alleles that are population specific; and (iii) have significant F _IS values (mean overall F _IS= 0.194) probably due to a combination of Wahlund effects resulting from fine-scale genetic differentiation within populations and the presence of null alleles. Our results imply that massasauga populations may be genetically structured on an extremely fine scale even within continuous populations, possibly due to limited dispersal. Additional information is needed to determine if dispersal and mating behaviour within populations can account for this structure and whether the observed differentiation is due to random processes such as drift or to local adaptation. From a conservation perspective, our results imply that these massasauga populations should be managed as demographically independent units and that each has high conservation value in terms of containing unique genetic variation.     

Abundance and habitat preferences of the southernmost population of mink: implications for managing a recent island invasion

Since 2001 invasive American mink has been known to populate Navarino Island, an island located in the pristine wilderness of the Cape Horn Biosphere Reserve, Chile, lacking native carnivorous mammals. As requested by scientists and managers, our study aims at understanding the population ecology of mink in order to respond to conservation concerns. We studied the abundance of mink in different semi-aquatic habitats using live trapping (n = 1,320 trap nights) and sign surveys (n = 68 sites). With generalized linear models we evaluated mink abundance in relation to small-scale habitat features including habitats engineered by invasive beavers (Castor canadensis). Mink have colonized the entire island and signs were found in 79% of the surveys in all types of semi-aquatic habitats. Yet, relative population abundance (0.75 mink/km of coastline) was still below densities measured in other invaded or native areas. The habitat model accuracies indicated that mink were generally less specific in habitat use, probably due to the missing limitations normally imposed by predators or competitors. The selected models predicted that mink prefer to use shrubland instead of open habitat, coastal areas with heterogeneous shores instead of flat beaches, and interestingly, that mink avoid habitats strongly modified by beavers. Our results indicate need for immediate mink control on Navarino Island. For this future management we suggest that rocky coastal shores should be considered as priority sites deserving special conservation efforts. Further research is needed with respect to the immigration of mink from adjacent islands and to examine facilitating or hampering relationships between the different invasive species present, especially if integrative management is sought.     

Foundations of spatial ecology: the reification of patches through quantitative description of patterns and pattern repetition

Insect populations tend to be patchy, and the nature of the patches is a critical component of ecology. Predator-prey interactions, coexistence of competing species, survival of rare species as habitat is destroyed, and damage to crops are just a few examples of spatially-dependent ecological processes. For want of tractable quantitative approaches, understanding of spatial ecology has lagged far behind recognition of its importance. We assert that a quantitative foundation of a spatial ecology involves the reification of patches as objects of study. We introduce two new measures of patch dynamics: total covariance for comparing degrees of patchiness between populations, and quantile variance for quantifying the constancy of dispersion patterns through time. These new measures, in combination with the long-established spatial covariance from geostatistics, comprise a rudimentary toolbox for reification of patches and empirical field studies in spatial ecology.     

Genetic effects of habitat fragmentation on blue sucker populations in the upper Missouri River (<Emphasis Type="Italic">Cycleptus elongatus</Emphasis> Lesueur, 1918)

The blue sucker, Cycleptus elongatus, is a large catostomid fish that occurs in main stem rivers throughout the Mississippi basin of North America. Although not federally listed as threatened or endangered, populations are not considered stable in any of 21 states where they occur. Included in the range is the Missouri River, which flows more than 3,200 km from Montana to St. Louis, Missouri. Historically, C. elongatus was distributed continuously throughout the main stem Missouri and its major tributaries, but from 1952 to 1963, six major impoundments were constructed on the upper Missouri by the US Army Corps of Engineers. The resulting reservoirs have inundated and fragmented large riverine habitat from Yankton, South Dakota to the headwaters. C. elongatus still occurs in remnant stretches between reservoirs; however, little is known of the impacts of the dams on these populations. In order to test for such effects, 231 individuals from nine sites were genotyped at 14 variable microsatellite loci. An additional 142 individuals from six sites in the Mississippi River were also genotyped for comparative purposes. In the Missouri, allelic richness was reduced in inter-reservoir sites relative to those in the free flowing lower river. In addition, significant isolation by distance occurs in the Missouri, a pattern not present in the unimpounded Mississippi. These results are consistent with reduced intradrainage gene flow in the Missouri River and are the first to indicate effects of impoundments on genetic structure in the system. This information will assist governing agencies in making informed decisions regarding conservation of C. elongatus in the Missouri River drainage and throughout the range.     

Road avoidance and its energetic consequences for reptiles

Roads are one of the most widespread human‐caused habitat modifications that can increase wildlife mortality rates and alter behavior. Roads can act as barriers with variable permeability to movement and can increase distances wildlife travel to access habitats. Movement is energetically costly, and avoidance of roads could therefore impact an animal's energy budget. We tested whether reptiles avoid roads or road crossings and explored whether the energetic consequences of road avoidance decreased individual fitness. Using telemetry data from Blanding's turtles (Emydoidea blandingii; 11,658 locations of 286 turtles from 15 sites) and eastern massasaugas (Sistrurus catenatus; 1,868 locations of 49 snakes from 3 sites), we compared frequency of observed road crossings and use of road‐adjacent habitat by reptiles to expected frequencies based on simulated correlated random walks. Turtles and snakes did not avoid habitats near roads, but both species avoided road crossings. Compared with simulations, turtles made fewer crossings of paved roads with low speed limits and more crossings of paved roads with high speed limits. Snakes made fewer crossings of all road types than expected based on simulated paths. Turtles traveled longer daily distances when their home range contained roads, but the predicted energetic cost was negligible: substantially less than the cost of producing one egg. Snakes with roads in their home range did not travel further per day than snakes without roads in their home range. We found that turtles and snakes avoided crossing roads, but road avoidance is unlikely to impact fitness through energetic expenditures. Therefore, mortality from vehicle strikes remains the most significant impact of roads on reptile populations.     

A comparison of RAPD versus microsatellite DNA markers in population studies of the massasauga rattlesnake

We compared genetic differentiation among populations of the threatened massasauga rattlesnake (Sistrurus c. catenatus) using two types of nuclear molecular markers: randomly amplified polymorphic DNA (RAPD) markers and microsatellites. Analyses of molecular variance (AMOVA) and G(ST) and F(ST) analyses indicated that levels of among-population differentiation between regional populations (>100 km) were comparable for both markers. However, microsatellites were superior in population assignment tests and at discerning fine-scale genetic differentiation between subpopulations separated by tens of kilometers. These results argue that both types of markers are suitable for defining broad-scale genetic structures in snake populations and can provide important inputs into conservation initiatives of focal taxa. However, our analyses suggest that microsatellites 3re better for detecting structure at limited spatial scales.