Abiotic Habitat Variables Research Articles

Habitat selection and population status of breeding Wood Snipe Gallinago nemoricola in an alpine meadow in Sichuan, China

Summary The Wood Snipe Gallinago nemoricola is one of the least known shorebird species, and its habitat associations are very poorly understood. Here we provide the first assessment of the habitat use of the Wood Snipe during the breeding season. Between May and July 2021 at a 4-km2 alpine meadow in Sichuan province, China, we conducted population surveys and behavioural observations to identify sites where breeding Wood Snipe occurred and foraged. We quantified the habitat characteristics and food resource availability of these sites and compared them with randomly selected “background” sites. Comparison between 34 occurrence sites and 25 background sites indicated that during the breeding season, Wood Snipes are not distributed evenly across alpine meadow habitats, but preferred habitats in the lower part (3,378–3,624 m) of the alpine meadow with intermediate levels of soil moisture. In addition, comparison between 17 foraging sites and 24 background sites showed that the Wood Snipe tended to forage at sites with higher soil fauna abundance. We found weak evidence for denser vegetation cover at its height and no evidence for other biotic habitat variables such as vegetation composition or other abiotic habitat variables such as slope, soil penetrability, or disturbance level to influence Wood Snipe habitat associations. Our results suggest that the actual distribution range of the Wood Snipe during the breeding season may be smaller than expected from the extent of apparently suitable habitat. We advise caution in evaluating the potential habitat availability and distribution of the Wood Snipe, and call for further research to better understand the ecology of this rare species to inform its conservation.

Cost-effective use of aerial imagery to quantify faunal-habitat associations across multiple spatial scales

We investigated the utility of publicly available map products to identify faunal-habitat associations to inform fisheries management. The influence of structural and abiotic variables on the abundance of 4 focal species (red drum Sciaenops ocellatus, spotted seatrout Cynoscion nebulosus, blue crab Callinectes sapidus, and brown shrimp Farfantepenaeus aztecus) was examined at multiple spatial scales in the Mission-Aransas estuary, Texas, USA. Structural habitat data were derived from the 2004 Benthic Atlas of Texas and paired with species abundance and hydrographic data collected by the Texas Parks and Wildlife Department’s Fisheries Independent Monitoring program. Blue crab and brown shrimp distributions at the ecosystem scale were driven primarily by abiotic factors such as salinity and distance to inlet, but structural habitat became relatively more important at smaller spatial scales. Variation in spotted seatrout abundance was primarily driven by seagrass and saltmarsh extent at the ecosystem scale but was driven by abiotic factors at the sub-region scale. Red drum distribution was driven primarily by abiotic factors, and association with structural habitats was bay-specific; there was no clear pattern in the influence of spatial scale on the relative importance of structural versus abiotic habitat variables for red drum. Results demonstrate that leveraging existing mapping efforts can allow fisheries managers to incorporate habitat data into fisheries management when funding or logistical challenges may otherwise prevent habitat monitoring at management-relevant scales. More research is warranted to investigate the temporal limitations to this approach, such as identifying the ‘shelf life’ of historical mapping products for utility in fisheries management.

Improved understanding and prediction of freshwater fish communities through the use of joint species distribution models

Two primary goals in fisheries research are to (i) understand how habitat and environmental conditions influence the distribution of fishes across the landscape and (ii) make predictions about how fish communities will respond to environmental and anthropogenic change. In inland, freshwater ecosystems, quantitative approaches traditionally used to accomplish these goals largely ignore the effects of species interactions (competition, predation, mutualism) on shaping community structure, potentially leading to erroneous conclusions regarding habitat associations and unrealistic predictions about species distributions. Using two contrasting case studies, we highlight how joint species distribution models (JSDMs) can address the aforementioned deficiencies by simultaneously quantifying the effects of abiotic habitat variables and species dependencies. In particular, we show that conditional predictions of species occurrence from JSDMs can better predict species presence or absence compared with predictions that ignore species dependencies. JSDMs also allow for the estimation of site-specific probabilities of species co-occurrence, which can be informative for generating hypotheses about species interactions. JSDMs provide a flexible framework that can be used to address a variety of questions in fisheries science and management.

Soil Moisture Controls the Thermal Habitat of Active Layer Soils in the McMurdo Dry Valleys, Antarctica

AbstractAntarctic soil ecosystems are strongly controlled by abiotic habitat variables. Regional climate change in the McMurdo Dry Valleys is expected to cause warming over the next century, leading to an increase in frequency of freeze‐thaw cycling in the soil habitat. Previous studies show that physiological stress associated with freeze‐thaw cycling adversely affects invertebrate populations by decreasing abundance and positively selecting for larger body sizes. However, it remains unclear whether or not climate warming will indeed enhance the frequency of annual freeze‐thaw cycling and associated physiological stresses. This research quantifies the frequency, rate, and spatial heterogeneity of active layer freezing to better understand how regional climate change may affect active layer soil thermodynamics, and, in turn, affect soil macroinvertebrate communities. Shallow active layer temperature, specific conductance, and soil moisture were observed along natural wetness gradients. Field observations show that the frequency and rate of freeze events are nonlinearly related to freezable soil moisture (θf). Over a 2 year period, soils at θf < 0.080 m3/m3 experienced between 15 and 35 freeze events and froze rapidly compared to soils with θf > 0.080 m3/m3, which experienced between 2 and 6 freeze events and froze more gradually. A numerical soil thermodynamic model is able to simulate observed freezing rates across a range of θf, reinforcing a well‐known causal relationship between soil moisture and active layer freezing dynamics. Findings show that slight increases in soil moisture can potentially offset the effect of climate warming on exacerbating soil freeze‐thaw cycling.

Habitat diversity and connectivity govern the conservation value of restored aquatic floodplain habitats

Floodplains have been strongly altered by human activities such as channelization and other river regulations. Globally, there is a growing interest in their restoration because of an increasing understanding of the ecological importance of these habitats for feeding, spawning, nursery or overwintering of aquatic species. In this study, a large floodplain restoration project of the upper Danube River was used to investigate colonization and succession patterns of fish, macroinvertebrates, macrophytes and periphyton in relation to abiotic habitat variables that can be restored through ecosystem management. Highest species diversity was detected near the contact zones of the floodplain channel to the main stem of the Danube, and in the transition zones of river sections (RS) and oxbow lakes (OS). The highest proportions of all taxa (82%) and of distinctive species (22%) were detected in RS, followed by OS (66% of all taxa, 8% distinctive species) and floodplain ponds (FP, 47% of all taxa, 5% distinctive species). The habitat types RS, OS and FP significantly differed in overall community composition and their colonization processes comprising fast colonization of current-adapted specialists in RS, and mostly generalist species in OS and FP. Our results indicate that restoration of floodplain habitats should not only consider the re-establishment of maximum connectivity, but also provide a mosaic of distinct habitat types with different degrees of connectivity and disturbance. Each habitat type in the floodplain supported a unique assemblage of species, which suggests that such habitat mosaics can facilitate exceptionally diverse ecosystems.

Random forests to evaluate biotic interactions in fish distribution models

Previous research indicated that high predictive performance in species distribution modelling can be obtained by combining both biotic and abiotic habitat variables. However, models developed for fish often only address physical habitat characteristics, thus omitting potentially important biotic factors. Therefore, we assessed the impact of biotic variables on fish habitat preferences in four selected stretches of the upper Cabriel River (E Spain). The occurrence of Squalius pyrenaicus and Luciobarbus guiraonis was related to environmental variables describing biotic interactions (inferred by relationships among fish abundances) and channel hydro-morphological characteristics. Random Forests (RF) models were trained and then validated using independent datasets. To build RF models, the conditional variable importance was used together with the model improvement ratio technique. The procedure showed effectiveness in identifying a parsimonious set of not correlated variables, which minimize noise and improve model performance in both training and validation phases. Water depth, channel width, fine substrate and water-surface gradient were selected as most important habitat variables for both fish. Results showed clear habitat overlapping between fish species and suggest that competition is not a strong factor in the study area.

Modeling freshwater mussel distribution in relation to biotic and abiotic habitat variables at multiple spatial scales

The habitat requirements of many native freshwater mussels remain unclear despite their imperiled status and ecological importance. To explore scale-specific habitat associations in the three genera of mussels found in the western United States (Anodonta, Gonidea, and Margaritifera) we used a multiscale random forest modeling approach to assess functional habitat parameters throughout a 55 km segment of the upper Middle Fork John Day River in northeastern Oregon. We characterized mussel occurrence and density with respect to the hierarchical, hydrogeomorphic structure by sampling reaches of varying valley confinement and channel units nested within individual reaches. Each genus exhibited unique longitudinal trends and channel unit-use patterns. In particular, the large-scale longitudinal trends in Margaritifera occurrence were associated with hydrogeomorphic characteristics at the reach and channel unit scale, with Margaritifera densities peaking in narrow valley segments and in riffles and runs. At the scale of the channel unit, all mussel genera responded to variation in physical habitat characteristics, particularly those that indicated more stable parts of the channel. Our results suggest that spatial patterns in freshwater mussels are associated with the hierarchical structuring of the lotic ecosystem and may provide guidance to restoration efforts.

Spatial Distribution of Fishes in Hydropeaking Tributaries of Lake Superior

Deviation from a river's natural flow regime is considered to be one of the most serious and continuing threats to lotic ecosystems. Peaking hydroelectric facilities, which are designed to adjust the level of power generation in accordance with hourly energy demand, can dramatically alter flows and temperatures and ultimately lead to changes in the quantity and quality of habitat available to fish. In this study, we examine the spatial distribution of river fishes, benthic invertebrates and organic matter along lateral and longitudinal gradients in two hydropeaking and eight natural Lake Superior tributaries in Ontario, Canada. This study demonstrates that (i) hourly variation in flow, caused by hydropeaking, results in a varial zone that supports significantly fewer fish than the adjacent permanently wetted channel and (ii) strong longitudinal gradients in fish biomass, particularly for sedentary species such as slimy sculpin (Cottus cognatus), exist in regulated rivers, and fish biomass is up to four times greater at sites directly below the peaking dams than at sites further downstream or in nearby natural rivers. Gradients in the spatial distribution of fishes closely follow changes in food resources such as benthic organic matter and invertebrates, suggesting that these gradients are driven by spatial shifts in food availability and are ultimately caused by gradients in abiotic habitat variables. Monitoring and assessment efforts should take into account that lateral and longitudinal gradients exist in regulated rivers, and this understanding must be incorporated into sampling programmes. Failing to do so could alter the interpretation of river productivity, integrity and health. Copyright © 2013 John Wiley & Sons, Ltd.

Linking temperate demersal fish species to habitat: scales, patterns and future directions

AbstractAdoption of the ecosystem approach to fisheries management relies on recognition of the link between fish and other components of the ecosystem, namely their physical and biological habitat. However, identifying the habitat requirements of marine fishes and hence determining their distribution in space and time is scientifically complex. We analysed the methodologies and findings of research on temperate, demersal fish habitat requirements to highlight the main developments in this field and to identify potential shortfalls. Many studies were undertaken over large spatial scales (≥100s km2) and these generally correlated abundances of fish to abiotic variables. Biological variables were accounted for less often. Small spatial scale (≤m2), experimental studies were comparatively sparse and commonly focused on biotic variables. Whilst the number of studies focusing on abiotic variables increased with increasing spatial scale, the proportion of studies finding significant relationships between habitat and fish distribution remained constant. This mismatch indicates there is no justification for the tendency to analyse abiotic habitat variables at large spatial scales. Innovative modelling techniques and habitat mapping technologies are developing rapidly, providing new insights at the larger spatial scales. However, there is a clear need for a reduction in study scale, or increase in resolution additional to the integration of biotic variables. We argue that development of sound predictive science in the field of demersal fish habitat determination is reliant on a change in focus along these lines. This is especially important if spatial management strategies, such as Marine Protected Areas (MPA) or No Take Zones (NTZ), are to be used in future ecosystem‐based approaches to fisheries management.

The effects of weirs on structural stream habitat and biological communities

Summary1. Most of the world’s rivers are affected by dams and weirs. Information on the quantitative and qualitative effects of weirs across biological communities is crucial for successful management and restoration of stream ecosystems. Yet, there is a lack of comprehensive studies that have analysed the serial discontinuity in direct proximity of weirs including diverse taxonomic groups from algae to fish.2. This study compared the abiotic stream habitat characteristics upstream and downstream of weirs as well as their effects on the community structure of periphyton, aquatic macrophytes, macroinvertebrates and fish at five different study rivers.3. Physicochemical habitat characteristics discriminated strongly between upstream and downstream sides of weirs in terms of water depth, current speed, substratum composition and the transition between free‐flowing water and interstitial zone. Accordingly, abundance, diversity, community structure and functional ecological traits of all major taxonomic groups were indicative of serial discontinuity, but the discriminative power of individual taxonomic groups strongly differed between rivers.4. The simultaneous inclusion of abiotic habitat variables, taxonomic diversity and biological traits in multivariate non‐metric multidimensional scaling was most comprehensive and powerful for the quantification of weir effects. In some cases, the intrastream discrimination induced by weirs exceeded the variation between geographically distant rivers of different geological origin and drainage systems. Community effects were generally detectable on high levels of taxonomic resolution such as family or order level.5. Synthesis and applications. River sections in spatial proximity to weirs are affected seriously and should be included in the ecological assessments of the European Water Framework Directive. Multivariate models that include several taxonomic groups and physicochemical habitat variables provide a universally applicable tool for the ecological assessment of impacts on serial discontinuity and other stressors on stream ecosystem health.

Impact of proximity to a pathway on orchid pollination success in Huanglong National Park, South-West China

Although edge effects often significantly alter abiotic habitat variables, and the performance and behaviour of plant and animal species, they are rarely taken into account when designing nature reserves or managing the movement of visitors within reserves. In this study, we examined the effects of proximity to a habitat edge, created by a visitor pathway, on reproductive success of the orchids Phaius delavayi and Ponerorchis chusua within the Huanglong National Park, China. Parallel transects were established at different distances from the pathway to test the effects of proximity to the pathway on male and female reproductive success in two consecutive years. For Phaius delavayi, percentage pollinarium removal and percentage fruit set showed significant variation between transects in both years, with plants in transects closer to the pathway having lower reproductive success. P. chusua showed the same trends except for pollinarium removal in one year. These results are consistent with the hypothesis that proximity to the pathway, which is used by a large number of visitors every day throughout the orchids’ flowering seasons, interfered with pollinator activity, depressing male and female reproductive success in both species. The impacts on reproductive success were significant for plants within approximately 10 meters of the pathway. Such edge effects may be common, and may need to be considered when designing nature reserves in which visitor activity is encouraged.

Site-level habitat models for the endemic, threatened Cheat Mountain salamander (Plethodon nettingi): the importance of geophysical and biotic attributes for predicting occurrence

The federally threatened Cheat Mountain salamander (Plethodon nettingi; hereafter CMS) is known to occur in approximately 70 small, scattered populations in the Allegheny Mountains of eastern West Virginia, USA. Current conservation and management efforts on federal, state, and private lands involving CMS largely rely on small scale, largely descriptive studies of habitat associations from a few sample sites. To address the critical need for quantitative data, we used an information-theoretic approach to elucidate site-level habitat relationships of CMS relative to a suite of biotic and abiotic habitat variables measured across the species’ range. We collected data on 18 explanatory habitat variables at CMS-occupied (n = 67) and random (n = 37) sites in the summer of 2006 and examined CMS habitat relationships using a priori, logistic regression models with information-theoretic model selection. Overall, results indicated that the probability of CMS occurrence at a fine spatial scale increased in areas with shallower depth to rock, areas proximal to rocky outcrops but distal to seeps, areas with higher densities of bryophytes, and areas with high densities of red spruce (Picea rubens) and eastern hemlock (Tsuga canadensis). Within the Allegheny Mountains, associations between CMS and abiotic habitat features appear to be important predictors of site-level occurrence, although vegetation associations interact to form more precise habitat relationships within forested landscapes. The information gained from our study should increase the capacity of managers to plan for the continued persistence and conservation of Cheat Mountain salamanders in this landscape.

Macrohabitat models of occurrence for the threatened CheatMountain salamander, Plethodon nettingi

The federally threatened Cheat Mountain salamander (Plethodon nettingi; hereafter CMS) is known to occur at approximately 70 small, scattered sites in the Allegheny Mountains of eastern West Virginia. We used a comparative modeling approach to explain the landscape-level distribution and habitat relationships of CMS in relation to a suite of biotic and abiotic habitat variables measured across the species' range. We collected data on 13 explanatory macrohabitat variables at CMS-occupied (n = 180) and random (n = 180) sites. We then examined CMS-macrohabitat relationships using a priori, logistic regression models with information-theoretic model selection, classification tree modeling, and discriminant function analysis. Among logistic regression models, a model containing the variables elevation, aspect, slope, and lithology received the strongest empirical support, although a model containing these variables and current vegetation type also received limited support. Variable selection within our classification tree and discriminant function modeling was consistent with logistic regression results. Common variables in all three approaches indicated that the probability of finding CMS across the species' range increased in areas at higher elevations and underlain by sandstone. Validation of models with empirical support using reserved data indicated that classification accuracy was ≥80% for all three analytical methods. Finally, we linked model outputs from all three methods to GIS coverage maps that predicted CMS occupancy within the study area. Our results indicate that geophysical and ecological characteristics measured at large spatial scales may be useful for quantifying salamander habitat relationships in forested landscapes, and more specifically increase the capacity of managers to locate and plan for the continued persistence and recovery of CMS.

Mixed‐species social aggregations in Madagascan tadpoles—determinants and species composition

The frequency, species composition, and determinants of mixed‐species tadpole aggregations were analysed under natural conditions in a dry forest of western Madagascar. Most aggregations (73%) were formed by more than one species, with up to four species per individual aggregation. Dyscophus insularis (Microhylidae) and Aglyptodactylus securifer (Mantellidae) were the most abundant species in these aggregations. Using a logistic regression model we analysed to what extent the presence and absence of aggregations in a pond can be predicted by its biotic and abiotic habitat variables. Aggregations are more likely in deep, clear ponds with little leaf litter cover on the bottom, while the overall density of invertebrate predators in the pond seems to play a minor role. Our observations suggest that the formation of mixed‐species aggregations in tadpoles of the Kirindy Forest in our system is primarily a reaction to vertebrate predators. Therefore, aggregation behaviour may play a key role in the ability of several anuran species to utilize these spawning waters that are unpredictable in regard to the presence of fish and other vertebrates.

Catchment scale patterns of aquatic hyphomycetes. The role of physicochemical variables and substrate composition in structuring conidial communities

Spatial dynamics of aquatic hyphomycete species were studied in four streams of a catchment in Hungary. Conidial pools at 11 sites were sampled by membrane filtration of stream water. Spatial relationships of the studied stream sites based on conidial communities were demonstrated by minimum spanning tree analyses. Metric multidimensional scaling was used to represent the similarity structure of the sites based on different sets of data. The evaluation of the results by procrustes analyses suggested that the effect of abiotic variables and the substrate composition on the structure of hyphomycete communities were both important, but not to the same degree. Ordination based on abiotic habitat variables showed somewhat higher similarity to ordination based on the hyphomycetes data than to ordination based on leaf litter data. The relationships between environmental variables and aquatic hyphomycete species were analysed by canonical correspondence analysis. The results suggested that altitude, water hardness and conductivity were the major factors correlated with the distribution of individual species. An alternative sampling technique for analysis of leaf litter composition in streams is discussed.

ASYMMETRY IN STRUCTURAL DEFENSES: INSIGHTS INTO SELECTIVE PREDATION IN THE WILD

Assessment of geographical patterns in fluctuating asymmetry (small, random differences between sides of bilateral characters) among populations shows promise as a tool to resolve the relative biomechanical importance of traits, in addition to being a possible indicator of habitat quality. We used 115 endemic freshwater populations of threespine stickleback (Gasterosteus aculeatus) from Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada, to explore the degree of concordance between geographical variation of asymmetry in a predator defense structure (bony lateral plates) and geographical variation in several indirect measures of predation regime as well as several abiotic habitat variables. We found a geographical cline in the population frequency of lateral plate asymmetries, with reduced asymmetry in the southern clear-water regions of the archipelago characterized by long reaction distances and greater chance of capture by predators, and elevated asymmetry in the northern stained-water regions with poor visibility and low chances of capture. Lateral plate asymmetry was strongly correlated with expression of several defensive armor traits, including total plate numbers among populations, mean cross-sectional diameter of stickleback with the dorsal and pelvic spines erect, and mean degree of overlap between the plates and spine supports. There were no significant correlations between frequency of asymmetric fish and any of our abiotic habitat variables. Stickleback with structural plate asymmetries had fewer trout-induced scars than symmetric fish in the significant majority of populations, and there was a decrease in structural plate asymmetry with age in stained-water habitats, suggesting that trout predators may be selectively removing asymmetric fish in some lakes. This study provides evidence that geographical variation in developmental stability of threespine stickleback, as seen in the frequencies of asymmetry, reflects differences among populations in the importance of structural defenses to fitness rather than differences in habitat quality, and that asymmetry may be a target of selection by predators in wild populations.