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Because of their proximity to oceanic waters, freshwater tidal forests are susceptible to impacts from future climate change and sea level rise. These wetlands are historically understudied and we conducted our study to improve the understanding of structural changes in forested wetlands as they become tidally influenced. Using 20 forested stands across a tidal gradient on the lower Apalachicola River, Florida we examined changes in forest structure (tree density, size classes), basal growth, sapling/shrub cover and richness, understory cover/richness, and coarse woody debris. Tidal wetlands had greater tree (>2.5 cm DBH) density compared to nontidal forests (1446 ± 159 and 962 ± 100 stems ha−1, respectively) and more small trees (2.5 to 5.0 cm DBH) (699 and 359 stems ha−1, respectively). Over a 3 y period (2007 to 2010), basal area increment ranged from −0.07 to 0.30 m2 ha−1 y−1 for tidal wetlands and 0.07 to 0.55 m2 ha−1 y−1 for nontidal wetlands. Both forests experienced tree mortality during the study that influenced basal area. Tidal wetland tree mortality appeared to result from saltwater intrusion while several nontidal forest plots were affected by downed trees during a winter wind storm. Mean sapling/shrub (<2.5 cm DBH) density and richness in tidal forests were more than twice that estimated for nontidal forests. Mean herbaceous cover in tidal wetlands (72 ± 4%) was significantly higher than nontidal forests (19 ± 4%) and dominated by perennial herbaceous plants as opposed to nontidal wetlands that were often dominated by tree seedlings. Mean, large, coarse, woody, debris biomass (>7.62 cm diameter) was significantly lower in tidal wetlands compared to nontidal wetlands. Results demonstrated that riparian forests can have large and sudden shifts in stand structure and species composition related to tidal influences where rivers approach the coast.
We examined vegetation changes in a mixed grassland-shrub community in eastern Colorado between 1999–2010, a period that encompassed both extreme drought and moisture recovery, as well as slightly higher than long term average temperatures. Shrub cover significantly increased while grass cover significantly decreased following the drought years of 2002–2003. Grass cover had still not fully recovered 7 y after the drought, primarily due to the slow recovery of blue grama (Bouteloua gracilis). Blue grama was no longer dominant in this community, becoming secondary in importance to alkali sacaton (Sporobolus airoides). Increase in shrub cover and density were especially notable in rabbitbrush (Ericameria nauseosa) and tree cholla (Cylindropuntia imbricata). Although rabbitbrush density declined in the drought, overall cover of remaining individuals increased, even during the drought. Cholla density increased by nearly 200 plants/ha from 543 plants/ha to 726 plants/ha, all post drought.
Tallgrass prairie is the most endangered ecosystem in North America, with less than one percent of its original extent remaining. The Nature Conservancy (TNC) has restored over 9000 ha of crop and fallow lands adjacent to native prairie with a primary goal of buffering remnant prairies to maintain plant community composition and reduce invasion by nonnative plants. We tested the efficacy of this approach by measuring plant community parameters at four TNC prairie restoration sites in Iowa, Minnesota, Illinois, and Indiana. We tested whether restorations protected remnant prairies from nonnative plants by comparing the effect of neighboring land use on community composition along transects running from the prairie edges toward the interior. Nonnative dominance increased from interior to edges by 78% when adjacent to roads/abandoned lands and by 29% when adjacent to crops, but remained even (and low) when adjacent to prairie restorations (nonsignificant increase of 5–11% for high and low diversity restorations). Native plant richness was maintained in prairies adjacent to restorations (nonsignificant losses of 0.03 species/0.25 m2 for low species richness restorations and 1.1 species/0.25 m2 for high species richness restorations from interior to edge), significantly less than the 3.8 species/0.25 m2 lost from interior to edge next to roads/abandoned lands. The change in native richness next to cropland was intermediate, but nonsignificant, with a loss of 1.4 species/0.25 m2. These results suggest that managers may be able to buffer remnant prairies against nonnative species invasion and protect native plant diversity by targeting restorations of roadsides, abandoned lands, and other adjacent areas dominated by non-native plants.
Describing fish habitat associations and their relevance to conservation remains a central challenge in stream fish ecology. Unfortunately, there are limited opportunities to investigate these associations in unaltered systems and identify critical habitats used by native fishes. Investigation of fish habitat associations in tallgrass prairie is especially vital, owing to their widespread destruction. Our study aim was to identify habitat factors associated with the distribution and density of fishes in two protected tallgrass prairie stream watersheds in eastern Kansas: Kings Creek on the Konza Prairie Biological Station (KPBS) and Fox Creek on the Tallgrass Prairie National Preserve (TPNP). We sampled fishes and measured eight habitat variables at three sites on KPBS (2006–2011) and four sites on TPNP (2008–2011). Multiple regression suggested that species richness was positively associated with pool area (partial r = 0.70) and discharge (partial r = 0.50) in Fox Creek (df = 15, Adj. R2 = 0.60, P < 0.001). In Kings Creek, species richness was only associated with pool area (df = 17, R2 = 0.44, P < 0.001). Redundancy analyses showed common prairie fish species exhibit ontogenetic habitat associations, partitioning adults in deep and juveniles in shallow pools. Strong species area relationships in these minimally altered systems indicates large volume habitats have greater species richness, suggesting water diversions or extractions that reduce habitat are likely to cause declines in native biodiversity.
The introduction of exotic fish can have profound effects on wetland ecosystems, making it important to understand wetland vulnerability to invasion. Recently, African jewelfish (Hemichromis letourneuxi) have invaded wetlands in a hydrologically altered agricultural landscape at Archbold Biological Station in peninsular Florida. We sampled 45 wetlands using minnow traps to determine the current distribution and relative abundance of African jewelfish and brown hoplo (Hoplosternum littorale), another established exotic fish. We examined whether wetland area, depth, or distance to nearest ditch influenced the distribution or catch-per-unit-effort (CPUE) of these species. We also measured the total length and weight of 864 African jewelfish and examined gut contents to determine the body condition and diet of this newly established population. African jewelfish were found in only 22% of wetlands but were the most frequently captured vertebrate in those wetlands (mean 8.30 ± 0.81 se individuals/trap-night). Wetland area was the only significant predictor of African jewelfish distribution and was positively correlated with the combined CPUE of African jewelfish and brown hoplo. Distance to nearest ditch and exotic fish CPUE were inversely correlated. None of the factors examined influenced brown hoplo distribution. The African jewelfish were in good condition, and their diet consisted primarily of fish and macroinvertebrates. Additional research is needed to determine the effects of African jewelfish on native freshwater communities.
Predation pressure has often been postulated as a major selective force for the evolution of life histories, with high predation (particularly on small sizes) resulting in a fast-living strategy characterized by fast growth, early maturation, and short lifespan. However, due to the difficulty of assessing actual predation pressure in the wild, evidence for a role of predation in life-history evolution is rare. We examined the relationship between avian predation and life-history strategy in replicate populations of fast and slow-living garter snake ecotypes. To assess avian predation, we first compiled a list of known and suspected predators based on direct observations of predation events recorded in our long term detailed field notes from 1978 – present. Furthermore, we added to this list with published records of snake predation involving avian species known to occur in our study site, and a novel method of inferring predator identity via analysis of bill marks on live snakes. Using this list of candidate predators, we conducted surveys quantifying predator incidence in replicate habitats of both ecotypes. We found that known and suspected predators are more abundant in habitats of the fast-living ecotype than in those of the slow-living ecotype. We also show a higher incidence of bill marks on slow-living snakes, which may indicate an increased effectiveness at escaping predation attempts. In general, we provide evidence to suggest that predation pressure may indeed have been an important selective force in the evolution of fast growth and early maturation in the fast-living ecotype and may continue to constitute an important source of extrinsic mortality leading to differences in lifespan between the two ecotypes.
We examined nest success and nest site selection of red-headed woodpeckers (Melanerpes erythrocephalus) in east-central Illinois. Overall nest success, estimated from a constant survival logistic-exposure model, was 56%. Cavities at greater height had greater success and daily survival rates increased with nest age. We also compared habitat variables at nest and random sites. Red-headed woodpeckers nested more frequently in snags than expected and habitat surrounding nest cavity trees had more cavities than habitat surrounding random trees, which were generally taller than nest cavity trees. Thus, the immediate preservation or creation of large diameter snags and snags high above the ground will likely improve nesting habitat and nest success of red-headed woodpeckers.
Although extensively studied in upland landscapes, little has been published regarding Eastern Wild Turkey (Meleagris gallopavo silvestris) nest site selection and reproductive ecology in bottomland systems. Wild Turkeys in these systems face unique conditions, such as persistent flooding, so facets of nesting ecology observed in primarily upland landscapes may not apply directly to Wild Turkeys in bottomland systems. We studied nesting ecology of radio-marked female Wild Turkeys during six nesting seasons (2002–2004, 2008–2010) in a bottomland hardwood system in south-central Louisiana. We studied landscape level nest site selection at three spatial scales (200 m, 400 m, and 800 m) and found Wild Turkeys selected nesting locations in areas that offered greater proportions of nonflooded bottomland forests and higher forest edge density than generally available across the study site at all scales. At smaller spatial scales, forest openings were also important to nest site selection, while at large scales, nest location was negatively related to landscape diversity. All nests were located in dry higher elevation forests (n = 35) or forest openings (n = 6). These habitats were likely selected because they offered protection from flood-related nest mortality and access to brood-rearing habitat. At the micro habitat scale, ground level cover was important to nest site selection, and likely provided protection from ground predators. Nests were often associated with small recent breaks in the canopy, presumably as a response to the resulting growth in understory cover. Wild Turkeys avoided nesting in managed forest stands with large areas of open canopy, likely because rapid successional growth in these areas made understory growth too dense. Nest predation was the greatest cause of nest failure (55%). Nesting rates (60%) and female success rates (24%) were among the lowest reported for the species, whereas nest success (39%) was near the range wide average. Reproductive performance may have been hampered by a scarcity of quality nesting habitat due to flooding and generally sparse understory vegetation, which left nests vulnerable to predation. Despite low nesting rates and female success, there was no evidence of a declining population on our study area. We suspect this may be a result of either high poult survival due to high quality brood-rearing habitat or because high female survival rates allow individual birds multiple chances to successfully reproduce.
We examined effects of forest treatments on Cerulean Warbler relative abundance and spatial attributes of territories between pretreatment (2007–2008) and post treatment (2009–2010) years in Yellowwood and Morgan-Monroe state forests in southern Indiana. Three management units received uneven aged harvests (patch cuts), three units received even aged harvests (shelterwood and clearcut), and three units received no treatment (control). Cerulean Warblers occurred in greater abundance at study sites that received even aged harvests than in uneven aged harvested stands based on point - count surveys. Cerulean Warblers were attracted to areas with large canopy gaps resulting from even-aged harvests. Territory sizes were not significantly smaller after harvest treatments. Cerulean Warbler territories on harvested and control sites were clustered, closer to roads and streams, and on steeper slopes with an eastern aspect compared to random sites. Our relative abundance estimates suggested that Cerulean Warblers responded positively to some types of forest treatments during the 2 y post harvest period.
It is now well known that biodiversity in agricultural landscapes can be increased by converting production lands (i.e., farmland) into more natural habitat. However, it remains relatively unknown to what extent biodiversity can also be enhanced by changing the composition and configuration of farmland per se. We examined relationships between farmland structure and avian biodiversity in six watersheds representing a gradient in rowcrop intensity in the American Mid-west. We used canonical correspondence analysis (CCA) to model relationships at the site (0.8 ha), field (21 ha), section (165 ha) and watershed (4000–18,000 ha) extents to explore these questions: (1) At what spatial extent do birds respond most strongly to farmland structure? (2) Which farmland variables are most important? (3) Does avian biodiversity increase with increasing farmland heterogeneity? Most variation in bird assemblages was explained at the field versus the site or section extents. Of the top 20 field-extent variables in CCA, most important were: % woodland, an index of compositional heterogeneity (the modified Simpson's evenness index, MSIEI), % rowcrop, % core pasture (i.e., away from an edge), and edge density. Eighteen species were associated with woodland; their richness increased with woodland from 0% to 10%. Nine species were associated with rowcrop; their richness decreased two-fold with a change in rowcrop from 80% to 3%. Twelve species were associated with farmland heterogeneity; their richness increased four-fold with more field cover heterogeneity (MSIEI) and decreased three-fold with increasing mean field size from 1.2 to 7 ha. Field-extent α and β species richness were significantly higher than expected in the null model in the two most heterogeneous watersheds and lower in the two most intensely farmed watersheds. Differences among watersheds were significant and evident in the CCA ordination plot. Our results show empirically that policies to influence farmland heterogeneity could provide a conservation benefit to avian biodiversity.
Bird aircraft collisions (bird strikes) are a recognized safety hazard and land uses that attract birds hazardous to aircraft should be avoided on and near airports. Many airfields contain large areas of anthropogenic grassland habitats, often dominated by cool season grasses. Land managed as native warm season grasses (NWSG) potentially could increase bird strike hazards on and near airports by attracting hazardous birds and harboring small mammals that are prey for hazardous raptors. We investigated bird and small mammal communities at three NWSG areas and three adjacent on airfield grassland areas in western Ohio, U.S.A. to determine whether NWSG increased bird strike hazards. Species specific differences in bird abundance and density were evident between the two landcover types, presumably the result of differences in plant community characteristics. Seven species of birds were found exclusively in NWSG or airfield grasslands. Birds of species categorized as ‘moderate’ to ‘extremely high’ in regard to hazard (severity) level to aircraft accounted for only 6% and 2% of all birds observed in airfield grasslands and NWSG areas, respectively. Small mammal capture success was approximately three times higher in NWSG areas, although raptor abundance did not differ between the two landcover types. Our findings suggest that NWSG might be considered a viable land use adjacent to airfields; however, similar research at additional locations, including larger NWSG areas, should be conducted.
Despite the importance of winter roosts to bat ecology, much less is known about tree roosts used by bats in winter than in summer. Rafinesque's big-eared bat (Corynorhinus rafinesquii) and southeastern myotis (Myotis austroriparius) are species of concern whose winter tree roost selection may be constrained by seasonal flooding in cypress-gum swamps. To evaluate winter roost selection by these species, we compared characteristics of winter roosts to trees not occupied in winter and to summer roost trees in the Oconee River floodplain, Laurens County, Georgia. We located 23 Rafinesque's big-eared bat winter roosts and 5 southeastern myotis winter roosts by climbing and visually inspecting hollow trees and by radio telemetry. We analyzed differences between used and unused trees in winter and between winter and summer roosts. Despite extensive flooding in winter, Rafinesque's big-eared bats roosted in cypress-gum swamps in summer and winter. Accordingly, they used similar large hollow water tupelo (Nyssa aquatica) in both seasons, although roost entrances were higher in winter. In contrast, southeastern myotis roosted in cypress-gum swamps in summer and switched to a diverse hardwood floodplain forest with shallower flood waters in winter. As a result they used smaller roosts in different tree species in winter than in summer. The divergent roosting habits in winter are likely due to the height of roost entrances in relation to flood waters. In summer Southeastern myotis use basal openings that are submerged during winter flooding, whereas Rafinesque's big-eared bats use openings located higher on the tree bole that are not submerged. Therefore, management for southeastern myotis may require provision of separate summer and winter roosting habitats.
In 1994 two 0.65 ha deer exclosures were built in a second growth forest in northeastern Pennsylvania, one under an oak-maple canopy and the other under eastern hemlock. We hypothesized that populations of white-footed mice (Peromyscus leucopus) outside the exclosures were depressed because of herbaceous cover removal by white-tailed deer (Odocoileus virginianus) and/or by acorn competition with deer and would be higher inside the exclosures. For 10 y, the small mammal communities were censured with one 10 × 4 Sherman live-trap grid in each exclosure and one control grid of identical dimensions immediately outside each exclosure. Paired-T comparisons between the oak-maple exclosure and control grids, and the hemlock exclosure and control grids indicated that more total males were captured in the oak-maple exclosure grid than in the oak-maple control grid. Although repeated-measures ANOVA indicated that habitat (tree canopy type) produced more differences in mice numbers than did the presence of the exclosures, it also demonstrated that numbers of large females fluctuated less in the oak-maple exclosure than in the corresponding control. A repeated measures ANOVA of Jolly-Seber population estimate indicated that more mice were trapped in the combined oak-maple and hemlock exclosure grids than in the combined control grids.
Decreases in white-tailed deer (Odocoileus virginianus) fawn recruitment have been noted at several locations across the Southeast. Understanding the reason for these decreases is important for management of deer populations. We monitored fawns from birth until 6 mo to examine age and cause specific mortality rates, at Fort Rucker, Alabama. During 2009–2010, 14 fawns were captured immediately after birth and monitored, with three surviving until 6 mo of age. Six of 7 predation events were attributed to coyotes (Canis latrans), and we determined coyote density in the study area during 2010, using DNA isolated from 44 coyote scats, to be 0.40 coyotes/km2. This study, like other recent studies in the Southeast, has found low fawn recruitment seems to be driven by coyote predation.
Reuse of ephemeral open cup nests by passerines is an uncommon behavior. We report the first case of nest reuse by federally endangered black-capped vireos (Vireo atricapilla). The initial use of the nest was unsuccessful because the clutch was parasitized by a brown-headed cowbird (Molothrus ater) during egg laying and then depredated during incubation. During reuse, apparently by the same pair of vireos, the nest escaped parasitism but was depredated when the nestlings were 7 d old. Although rare, this behavior may be an example of phenotypic plasticity in black-capped vireo nesting strategies. Despite failure in this instance, nest reuse may be adaptive if it reduces the risk of brood parasitism but could be maladaptive if it increases the risk of nest predation.