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.     

Stable isotope-based statistical tools as ecological indicator of pollution sources in Mediterranean transitional water ecosystems

N-stable isotope analysis of macroalgae has become a popular method for the monitoring of nitrogen pollution in aquatic ecosystems. Basing on changes in their δ¹⁵N, macroalgae have been successfully used as biological traps to intercept nitrogen inputs. As different nitrogen sources differ in their isotopic signature, this technique provides useful information on the origin of pollutants and their extension in the water body. However, isotopic fractionation potentially resulting from microbial nitrogen processing, and indirect isotopic variations due to effects of physicochemical conditions on algal nutrient uptake and metabolism, may affect anthropogenic N isotopic values during transportation and assimilation. This in turn can affect the observed isotopic signature in the algal tissue, inducing isotopic variations not related to the origin of assimilated nitrogen, representing a “background noise” in isotope-based water pollution studies.In this study, we focused on three neighbouring coastal lakes (Caprolace, Fogliano and Sabaudia lakes) located south of Rome (Italy). Lakes were characterized by differences in terms of anthropogenic pressure (i.e. urbanization, cultivated crops, livestock grazing) and potential “background noise” levels (i.e. nutrient concentration, pH, microbial concentration). Our aim was to assess nitrogen isotopic variations in fragments of Ulva lactuca specimens after 48 h of submersion to identify and locate the origins of nitrogen pollutants affecting each lake. δ¹⁵N were obtained for replicated specimens of U. lactuca spatially distributed to cover the entire surface of each lake, previously collected from a benchmark, unpolluted site. In order to reduce the environmental background noise on isotopic observations, a Bayesian hierarchical model relating isotopic variation to environmental covariates and random spatial effects was used to describe and understand the distribution of isotopic signals in each lake.Our procedure (i) allowed to remove background noise and confounding effects from the observed isotopic signals; (ii) allowed to detect “hidden” pollution sources that would not be detected when not accounting for the confounding effect of environmental background noise; (iii) produced maps of the three lakes providing a clear representation of the isotopic signal variation even where background noise was high. Maps were useful to locate nitrogen pollution sources, identify the origin of the dissolved nitrogen and quantify the extent of pollutants, showing localized organic pollution impacting Sabaudia and Fogliano, but not Caprolace. This method provided a clear characterization of both intra- and inter-lake anthropogenic pressure gradients, representing a powerful approach to the ecological indication and nitrogen pollution management in complex systems, as transitional waterbodies are.     

Perspectives on measurement of denitrification in the field including recommended protocols for acetylene based methods

Of the biogeochemical processes, denitrification has perhaps been the most difficult to study in the field because of the inability to measure the product of the process. The last decade of research, however, has provided both acetylene and¹⁵N based methods as well as undisturbed soil core andin situ soil cover sampling approaches to implementing these methods. All of these methods, if used appropriately, give comparable results. Thus, we now have several methods, each with advantages for particular sites or objectives, that accurately measure denitrification in nature. Because of the general usefulness of the acetylene methods, updated protocols for the following three methods are given: gas-phase recirculation soil cores; static soil cores; and the denitrifying enzyme assay also known as the phase 1 assay. Despite the availability of these and other methods, denitrification budgets remain difficult to accurately establish in most environments because of the high spatial and temporal variability inherent in denitrification. Appropriate analysis of those data includes a distribution analysis of the data, and if highly skewed as is typically the case, the most accurate method to estimate the mean and the population variance is the UMVUE method (uniformly minimum variance unbiased estimator). Geostatistical methods have also been employed to improve spatial and temporal estimates of denitrification. These have occasionally been successful for spatial analysis but in the attempt described here for temporal analysis the approach was not useful.Discussions of the importance of denitrification have always focused on quantifying the process and whether particular measured quantities are judged to be a significant amount of nitrogen. A second line of evidence discussed here is the extant genetic record that results from natural selection. These analysis lead to the conclusion that strong selection for denitrification must currently be occurring, which implies that the process is of general significance in soils.     

Restoration and creation of freshwater wetlands using seed banks

The minimum information about a seed bank needed for a wetland restoration or creation project is a species list. There are two basic techniques for determining the composition of seed banks: (1) mechanical separation of seeds from a volume of soil and (2) germination of seeds from a volume of soil under appropriate environmental conditions. The latter method always gives biased results. It is best to collect as many random samples as possible when sampling a wetland seed bank. These can be combined as needed for processing. Field studies in India have demonstrated that vestigial seed banks can be used to re-establish a former vegetation type in a monsoonal wet-land that had become overgrown by a species of grass. In less than a year, 9 of 1 I species in the vestigial seed bank were found growing in areas cleared of the grass. Vestigial seed banks of drained prairie wetlands in the northcentral United States contained a few wetland species after 70 years, although species diversity and seed density declined significantly after 20 to 30 years of drainage and cultivation. In Florida, U.S.A., wetlands have been established in strip-mined areas using donor soils from existing wetlands. Newly established wetlands quickly developed a dense cover of vegetation, although this vegetation often lacked many desirable wetland species. Experimental studies of soil moisture conditions using a seed bank from the Delta Marsh, Canada, demonstrated that soil moisture affected both the total number of seeds, and the relative proportion of seeds of each species that germinated from a seed bank. The density of seedlings of emergent wetland species in the treatments was directly proportional to soil moisture, while that of terrestrial annuals was inversely proportional. Emergent species made up nearly 90% of the seedlings in the wettest treatment and 0% in the driest.From a paper presented at the Third International Wetlands Conference, 19–23 September, 1988, University of Rennes, France.     

Effects of fire,topography and year-to-year climatic variation on species composition in tallgrass prairie

Native unploughed tallgrass prairie from Konza Prairie, Kansas, USA is described with respect to plant species compositional changes over a five year period in response to fire and topography. The principal gradient of variation in the vegetation is related to time since burning. Species show an individualistic response in terms of relative abundance to this gradient. Both the percentage of and cover of C₄ species and all grasses decrease as the prairie remains unburnt. Forb and woody plant species numbers and abundance increase along this gradient. A secondary gradient of variation reflects topography (i.e. upland versus lowland soils). Upland soils support a higher species richness and diversity. Upland and lowland plant assemblages are distinct except on annually burnt prairie. The interaction between burning regime, topography and year-to-year climatic variation affects the relative abundance of the plant species differentially. The most dominant species overall, Andropogon gerardii, was affected only by year-to-year variation (i.e. climate). Its position at the top of the species abundance hierarchy was unaffected by burning regime or soil type. The other dominant species showed a suite of varying responses to these factors.Deceased May, 1986.     

Bacterioplankton in the acidified Lake Gårdsjön

Total bacterial numbers in different strata of lake water and in inlet and outlet streams have been recorded during a yearly cycle. A calculated mean cell volume of 0.342 µm² has then been used to estimate bacterial biomass in the lake. Change of biomass during the year was substantial and the range was from about 0.1 g · m^–3 to about 1.0–1.2 g · m^–3. The seasonal development included a spring-early summer increase followed by a decrease to the minimum in July–August. Correlation between epi- and hypolimnion was high and in both strata two dominant autumn peaks in biomass appeared. With the exception of the last autumn peak the development of bacterial biomass was closely related to development of phytoplankton biomass and production.     

Rice hull and caryopsis discoloration diseases

In West Africa, rice is grown in three constrasting ecosystems, upland, phreatic, and lowland, which is characterized by differing water availability and soil properties. These ecosystems influence the predisposition of rice to disease problems, including the grain discoloration complex. Discoloration of the hull was found to be most severe in the upland, less in the phreatic, and least in the water-saturated lowland ecosystem. Caryopsis discoloration, however, showed no consistent pattern in relation to the three ecosystems and was not correlated with hull discoloration, indicating that other factors are involved.