Extirpation or Coexistence? Management of a Persistent Introduced Grass in a Prairie Restoration

Abstract Introduced perennial grasses are one of the greatest constraints to prairie restoration. Herbicides suppress but do not eliminate introduced grasses, so we explored the interaction of herbicide with two additional controls: heavy clipping (to simulate grazing) and competition from native species. A 50‐year‐old stand of the introduced perennial grass Agropyron cristatum (crested wheatgrass) in the northern Great Plains was seeded with native grasses and treated with herbicide annually for 7 years in a factorial experiment. Clipping was applied as a subplot treatment in the final 3 years. Both herbicide and clipping significantly reduced the cover of A. cristatum, but clipping produced an immediate and consistent decrease, whereas herbicide control varied among years. The cover of A. cristatum decreased significantly with increasing cover of a seeded native grass, Bouteloua gracilis (blue grama), suggesting that both top‐down (i.e., grazing) and bottom‐up (i.e., resource competition) strategies can contribute to A. cristatum control. No treatment had any effect on the seed bank of A. cristatum. Even in the most effective control treatments, A. cristatum persisted at low amounts (approximately 5% cover) throughout the experiment. The cover of B. gracilis increased significantly with seed addition and herbicide, and, after 7 years, was similar to that in undisturbed prairie. The total cover of native species increased significantly with clipping and herbicide, and species richness was significantly higher in plots receiving herbicide. Clipping season had no effect on any variable. In summary, no method extirpated A. cristatum, but clipping reduced its cover by 90% and doubled the cover of native species. Extirpation might not be a realistic goal, but relatively simple management allowed coexistence of native species.     

Exclosure fences around nests of imperiled Florida Grasshopper Sparrows reduce rates of predation by mammals

Increasing nest survival by excluding predators is a goal of many bird conservation programs. However, new exclosure projects should be carefully evaluated to assess the potential risks of disturbance. We tested the effectiveness of predator exclosure fences (hereafter, fences) for nests of critically endangered Florida Grasshopper Sparrows (Ammodramus savannarum floridanus) at a dry prairie site (Three Lakes; 2015–2018) and a pasture site (the Ranch; 2015–2016) in Osceola County, Florida, USA. We installed fences at nests an average of 8 days after the start of incubation, and nest abandonment after fence installation was rare (2 of 149 installations). Predation was the leading cause of failure for unfenced nests at both sites (48–73%). At Three Lakes, nest cameras revealed that mammals and snakes were responsible for 61.5% and 38.5% of predation events, respectively, at unfenced nests. Fences reduced the daily probability of predation (0.016 for fenced nests vs. 0.074 for unfenced nests). The probability that a fenced nest would survive from discovery to fledging was more than double that of unfenced nests (60.4% vs. 27.7%). However, we found no difference in daily nest survival at the Ranch between the year before nests were fenced (2015; 0.874) and the year when all but one nest were fenced (2016; 0.867) because red imported fire ants (Solenopsis invicta) were responsible for 86% of predation events at fenced nests at the Ranch. The use of cameras at fenced nests revealed that site‐specific differences in nest predators explained variation in fence efficiency between sites. Our fence design may be useful for other species of grassland birds, but site‐specific predator communities and species‐specific response of target bird species to fences should be assessed before installing fences at other sites.     

Drought mildly reduces plant dominance in a temperate prairie ecosystem across years

1. Shifts in dominance and species reordering can occur in response to global change. However, it is not clear how altered precipitation and disturbance regimes interact to affect species composition and dominance.
2. We explored community‐level diversity and compositional similarity responses, both across and within years, to a manipulated precipitation gradient and annual clipping in a mixed‐grass prairie in Oklahoma, USA. We imposed seven precipitation treatments (five water exclusion levels [?20%, ?40%, ?60%, ?80%, and ?100%], water addition [+50%], and control [0% change in precipitation]) year‐round from 2016 to 2018 using fixed interception shelters. These treatments were crossed with annual clipping to mimic hay harvest.
3. We found that community‐level responses were influenced by precipitation across time. For instance, plant evenness was enhanced by extreme drought treatments, while plant richness was marginally promoted under increased precipitation.
4. Clipping promoted species gain resulting in greater richness within each experimental year. Across years, clipping effects further reduced the precipitation effects on community‐level responses (richness and evenness) at both extreme drought and added precipitation treatments.
5. Synthesis: Our results highlight the importance of studying interactive drivers of change both within versus across time. For instance, clipping attenuated community‐level responses to a gradient in precipitation, suggesting that management could buffer community‐level responses to drought. However, precipitation effects were mild and likely to accentuate over time to produce further community change.

     

Effects of Patch-Burn Management on Dickcissel Nest Success in a Tallgrass Prairie

Abstract Grassland birds have declined more than any other North American habitat-associated bird community. Because most species of grassland birds evolved within heterogeneous landscapes created by the interaction of fire and grazing, traditional rangeland management that promotes homogeneity, including annual dormant-season burning combined with early-intensive grazing, might be partly responsible for these declines, especially in some regions of the Great Plains, USA. Recently, an alternative grassland management practice known as patch-burning has been promoted as a means of restoring heterogeneity to grasslands by mimicking the grazing-fire interaction that once occurred on the prairie before European settlement. From 2003 to 2004, we examined effects of patch-burning and traditional management (annual burning followed by early-intensive grazing) on the reproductive success of dickcissels (Spiza americana) in tallgrass prairie in Oklahoma. We monitored 296 dickcissel nests and found that dickcissel nesting phenology differed between traditional and patch-burned pastures. Specifically, dickcissels tended to initiate their nests later in the traditional pasture. Mean number of eggs laid and fledglings produced were similar between the treatments, but nest densities were higher in traditional pastures. Predation was the predominant cause of nest failure and was higher in traditional pastures than in patch-burned pastures. Brown-headed cowbird (Molothrus ater) parasitism was higher in traditional pastures than in patch-burned pastures. Overall, dickcissel nest success was higher in patch-burned pastures than in traditional pastures. The positive response of dickcissel nest success to patch-burn management provides further evidence that this practice can be a useful tool for grassland bird conservation. By creating a mosaic of different stature vegetation, patch-burn management enhances productivity of grassland bird species by providing a refuge area in the unburned patches that affords dickcissels and other nesting grassland birds some protection from the direct (e.g., trampling) and indirect (e.g., cowbird parasitism and predation) effects of grazing, which are not available under traditional management. Patch-burn management should be encouraged as a conservation strategy for grassland birds throughout the Great Plains.     

Occupancy of Mountain Plover and Burrowing Owl in Colorado

Abstract: Concern over the decline of grassland birds has spurred efforts to increase understanding of grassland bird-habitat relationships. Previous studies have suggested that black-tailed prairie dogs (Cynomys ludovicianus) provide important habitat for shortgrass prairie avifauna, such as mountain plover (Charadrius montanus) and western burrowing owl (Athene cunicularia hypugaea), although such studies are lacking in Colorado (USA). We used methods to estimate occupancy (ψ) of mountain plover and burrowing owl on prairie dog colonies and other shortgrass prairie habitats in eastern Colorado. Mountain plover occupancy was higher on prairie dog colonies (ψ = 0.50, 95% CI = 0.36–0.64) than on grassland (ψ = 0.07, 95% CI = 0.03–0.15) and dryland agriculture (ψ = 0.13, 95% CI = 0.07–0.23). Burrowing owl occupancy was higher on active prairie dog colonies (ψ = 0.80, 95% CI = 0.66–0.89) compared with inactive colonies (ψ = 0.23, 95% CI = 0.07–0.53), which in turn was much higher than on grassland (ψ = 0.01, 95% CI = 0.00–0.07) and dryland agriculture (ψ = 0.00, 95% CI ψ 0.00–0.00). Mountain plover occupancy also was positively correlated with increasing amounts of prairie dog colony in the landscape. Burrowing owl occupancy was negatively correlated with increasing amounts of prairie dog colony in the surrounding landscape. Our results suggest that actions to conserve mountain plovers and burrowing owls should incorporate land management to benefit prairie dogs. Because managing for specific colony attributes is difficult, alternative management that promotes heterogeneity may ensure that suitable habitat is available for the guild of grassland inhabitants.     

Development of retinal layers

A noticeable characteristic of nervous systems is the arrangement of synapses into distinct layers. Such laminae are fundamental for the spatial organisation of synaptic connections transmitting different kinds of information. A major example of this is the inner plexiform layer (IPL) of the vertebrate retina, which is subdivided into at least ten sublayers. Another noticeable characteristic of these retina layers is that neurons are displayed in the horizontal plane in a non-random array termed as mosaic patterning. Recent studies of vertebrate and invertebrate systems have identified molecules that mediate these interactions. Here, we review the last mechanisms and molecules mediating retinal layering.     

Hyperpigmentation of Chinchilla Stria Vascularis Following Acoustic Trauma

This report describes morphological alterations of the chinchilla stria vascularis seen 30 days after exposure to impulse noise. The observed changes included a dramatic increase in strial melanin content which occurred in 7 of 36 animals exposed to electronically synthesized impulses presented in various temporal patterns at either 135 or 150 dB peak SPL. In these animals, densely pigmented areas of stria 1.5 to 3 mm in length were found in the basal cochlear turn. Light and electron microscopic study revealed that these areas contained large numbers of melanin granules situated primarily in pale-staining cells of the middle layer of the stria. Unlike the pigment granules present in normal chinchilla stria, the melanosomes found in the noise-exposed material clearly showed ultrastructural features characteristic of eumelanin. Melanin granules were also observed in marginal and basal cells of the noise-exposed stria. In some cases, pigment granules which had apparently been expelled from the marginal cells were present in the endolymphatic space beneath Reissner's membrane and on the strial surface. These findings support the view that the melanin-bearing cells of the inner ear are capable of markedly increased activity in response to stressful conditions.     

One-Sided Barrier Impact of an International Railroad on Mongolian Gazelles

Abstract: We conducted a carcass census of Mongolian gazelles (Procapra gutturosa) along the Trans-Mongolian railroad in June 2005. We counted 241 gazelles that had died within the previous 12 months. Carcass numbers were greater on the southwestern side in the northern 3 zones, but we found carcasses only on the northeastern side in the southernmost zone. It suggests that impact of the railroad was stronger on one side and that the strength of this impact varied among regions.