Evaluation of statistical methods and sampling designs for the assessment of microhabitat selection based on point data

Nonlinear causal analysis reveals an effective water level regulation approach for phytoplankton blooms controlling in reservoirs

Reservoirs are a rapidly increasing water body providing water supply, irrigation, and many other benefits for human societies globally. However, due to changes in hydrological conditions, building reservoirs tends to bring adverse effects such as eutrophication and phytoplankton blooms, reducing the ecosystem service values. This study focuses on using the empirical dynamic modeling (EDM), an emerging approach for nonlinear analysis, to investigate the nonlinear causal relationship of water level fluctuation (WLF) on phytoplankton biomass and then develop a quantitative model guiding effective phytoplankton blooms controlling based on water level regulations in reservoirs. Specifically, with 9-year continued daily observed data in the Three Gorges Reservoir, we examined the causal effects of different WLF parameters on the dynamics of phytoplankton blooms for the first time. We found that the water level change in the past 24 h (ΔWL) has the strongest causal effect on the daily dynamics of phytoplankton biomass among all WLF parameters (ΔWL, |ΔWL|, and the water level), with a time lag of 2 days. Moreover, EDM revealed a nonlinear relationship between ΔWL and daily dynamics of phytoplankton biomass and achieved a successful prediction for the chlorophyll a concentration 2-day ahead. Further scenario analyses found that both the rise and fall of water level will significantly reduce the chlorophyll a concentration when phytoplankton blooms occur. Nevertheless, on the whole, the rising water level has a more substantial effect on phytoplankton blooms than falling the water level. This result reveals that regulating ΔWL is a simple and effective approach in controlling phytoplankton blooms in reservoirs. Our study reported the nonlinear causal effect of ΔWL on the dynamics of chlorophyll a and provided a quantitative approach guiding effective phytoplankton blooms controlling based on the water level regulation, which might have a broad application in algal blooms controlling in reservoirs and similar waterbodies.

Population survey of small rodents on islands located inside a region of endemism for hantavirus pulmonary syndrome

Ecological studies of rodent species, especially as reservoirs of zoonoses, can identify spatiotemporal conditions associated with irruptions of abundances, as well as predict areas and times with higher risk of disease transmission. The aims of this research were to describe and identify (i) the rodent community composition; (ii) their population structure and breeding season; (iii) temporal and spatial variations in their population abundance; and (iv) the environmental factors associated with these variations on islands of upper Paraná River Delta, a zone of endemism for hantavirus pulmonary syndrome (HPS) in Argentina (Entre Ríos and Santa Fe provinces). We carried out seasonal surveys over 3 years (2014–2017) with live capture traps on seven islands (natural protected areas and under livestock grazing). Three hundred seventy-seven sigmodontine rodents of seven species were captured. While the maximum richness was seven, only four species coexisted at most on an island at the same time. Although changes in reproduction were detected throughout the year, seasonality, land use, and vegetation structure did not explain changes in abundance of rodents. Rodent abundances were affected mainly by flooding-related factors and meteorological conditions (rainfall and temperatures). The recovery of rodent populations after river flooding was species-specific and heterogeneous. The abundance of Oxymycterus rufus and Akodon azarae was affected by El Niño Southern Oscillation (ENSO); A. azarae did not recover after the flood at least during the study period. After the flood, populations of Oligoryzomys flavescens, the reservoir of HPS, also declined; however, this species’ populations were the first to recover its numbers, becoming dominant in the post-flood rodent community.

Watershed farmland area and instream water quality co-determine the stream primary producer in the central Hengduan Mountains, southwestern China

As the main primary producer in stream ecosystems, periphyton is the fundamental of stream ecosystems and plays an essential role in maintaining stream biodiversity. The central Hengduan Mountains is one of the famous global biodiversity hotspots. However, for stream biodiversity conservations, the fundamental information about the spatial pattern of stream periphyton and the determining factors in this region remains largely unknown. To fill this gap, we investigated the spatial pattern of periphyton biomass (measured by chlorophyll a) in four typical streams in the central Hengduan Mountains and analyzed the driving factors, with the perspective of watershed land use and instream water quality. The results of our study found that farmland area, instream dissolved silicate (DSi), and water temperature (WT) had significant negative relationships with the stream periphyton biomass in the central Hengduan Mountains. However, the dissolved inorganic phosphorus (DIP) and dissolved inorganic nitrogen (DIN) had non-significant effects on the periphyton biomass in our study. Further analysis showed that the correlation between the ratio of farmland in the catchment and the DSi is non-significant (r = 0.028, P = 0.698), suggesting that the changes in farmland area will not affect the concentration of dissolved silicate in the stream. This reveals that the stream periphyton biomass was co-determined by the watershed farmland area and instream DSi and WT, but not nitrogen or phosphorus. These results highlight the importance of farmland management and instream DSi for stream ecosystems in the central Hengduan Mountains. Our study investigated the spatial pattern of the stream primary producer in the central Hengduan Mountains region and identified the main determining factors, which could improve our understanding of the high mountain stream ecosystems.

Are the Neglected Tipuloidea Crane Flies (Diptera) an Important Component for Subterranean Environments?

Usually, biospeleological studies focus on cave-specialist taxa showing strong adaptation to the subterranean environment, as their unusual morphological and ecological features represent intriguing case studies. On the other hand, species occurring in subterranean environments but without marked adaptations have been generally overlooked, probably because they are thought to be accidental and not very important for the ecosystem. Particularly exemplificative is the case of Tipuloidea crane flies (Diptera), which although abundant, are rarely considered in biospeleological studies. Here, by analyzing the crane fly occupancy, we observed that individuals occur within the shallowest areas of subterranean environments throughout the year, with a peak of presence during hot season. Crane flies occupy dark and warm areas close to the connection with surface and with smoother walls. Furthermore, we observed that the presence of crane flies is positively related to the abundance and the richness of cave predators, highlighting their importance for the sustainment of the local community. With this study we aim to stimulate future researches on these important, but still neglected cave species.

Assessment of survey protocol for estimates of abundance for elusive nocturnal primates

Abstract ContextEstimates of a species abundance and habitat preferences provide vital information on their status and the appropriate conservation management. For nocturnal arboreal primates, obtaining reliable estimates of these parameters is particularly challenging because of their cryptic behaviour, often resulting in a small number of detections. Although techniques are available for assessing the abundance of species with a low probability of detection, most require strict assumptions that are difficult to meet. AimsHere, we aimed to explore the possibility of improving nocturnal-primate abundance estimates when detection probability is low and to determine the minimal effort required to calculate reasonable estimates of their overall abundance and the effect of habitat type on abundance estimates. MethodsWe used count data obtained from spotlighting along line transects for estimating density of Bengal slow loris (Nycticebus bengalensis) in north-eastern Thailand with N-mixture hierarchical modelling, to run simulations of varying survey parameters and asses the effort needed to produce robust estimates based on the relative bias from each simulation. Key resultsN-mixture analysis showed that the data obtained from our study were still biased (9%), with a lambda of 1.79 lorises, detection probability of 0.11, 50 survey sites and a maximum of 12 sample occasions. The simulation results found that increasing the number of sample occasions to 14 per transect would produce an acceptable bias (<5%). ConclusionsWe recommend that future studies on nocturnal arboreal species should use preliminary surveys to gauge the specific lambda and probability of detection so as to establish the effort needed to produce reasonable estimates of abundance. ImplicationsOur study showed that count data obtained from spotlighting can be used to produce robust abundance estimates of nocturnal arboreal species. Unlike simple encounter rate, this method incorporates detection probability and habitat preferences, yet does not require additional trained field technicians.

Small rodent species on pig and dairy farms: habitat selection and distribution

BACKGROUND

Rodent species are common in livestock production systems, and some of them are considered serious pests because of the sanitary problems and economic losses they cause. Information about microhabitat selection by rodent species in livestock production systems is necessary for understanding rodent requirements and to contribute to effective prevention and development of control measures for pest rodent species. In this work we study microhabitat selection by rodent species that inhabit pig and dairy farms in central Argentina. Rodent trapping was conducted over three years (2008-2011) on 18 livestock farms, each one sampled seasonally during one year. To study habitat selection, microhabitat characterizations were performed describing 22 environmental variables in captured sites and random trap sites without captures.

RESULTS

With a trapping effort of 7333 Sherman and 7026 cage live trap-nights, 444 rodents of seven species were captured (including the murine pest species Rattus norvegicus, R. rattus and Mus musculus and four native species). The three murines selected characteristics related to building structure and/or to food sources availability/proximity, while Akodon azarae selected sites with tall herbatious vegetation.

CONCLUSIONS

We identified microhabitat characteristics that explain habitat distribution of small rodent species in these complex farm systems. This study contributes to broaden the integrated pest management of rodent pest species and could also contribute to the reduction of the use of rodenticides in these systems. © 2018 Society of Chemical Industry.

Livestock Grazing Shapes the Vegetation Structure and Subsequent Habitat Use by the Endangered Skipper Pyrgus ruralis lagunae (Lepidoptera: Hesperiidae)

Many species adapted to alpine and montane meadow ecosystems are at risk of extinction. The skipper Pyrgus ruralis lagunae Scott is a mountaintop butterfly restricted to San Diego County, CA, a federally listed endangered species, and is in imminent risk of extinction. Historically, P. r. lagunae was found in the Laguna and Palomar mountains. We did not detect the skipper in the Laguna Mountains, and the species has likely been extirpated from this area, which represents half of its historical range and is the type locality. We studied three populations on Palomar Mountain. Skippers primarily occupied areas close to creeks or in adjacent ravines at two nongrazed sites. The third site is grazed by cattle, and skippers were found close to the forest edge. At nongrazed locations, creek areas had higher cover of intermediate-height vegetation, more bare ground, and more flowers compared with unoccupied areas of the same meadow. The vegetation at occupied and unoccupied areas within the grazed meadow were similar. Even so, skippers occupied areas with more bare ground as well as greater species richness of flowering plants. A grazing exclosure was previously installed in an attempt to protect and enhance skipper habitat, but skippers did not use the dense grasslands that developed inside the exclosures. Contrary to the prevailing theory, protection from grazing did not improve skipper habitat. This illustrates how management based on inadequate biological information can hinder well-intentioned conservation efforts.