Ivlev's Electivity Index Research Articles

Breeding habitat selection of three sympatric species of Mediterranean warblers in eastern Spain

Understanding habitat selection patterns in congeneric species has raised special interest due to its importance when designing conservation strategies for the species. We analysed reproductive habitat selection of three coexisting warbler species in the eastern Iberian Peninsula. We detected the individuals by their vocalizations at 40 listening points in two study areas (Carcaixent and Alcoy). We used satellite images to identify different vegetation types and their availability. Reproductive habitat selection was analysed by the Ivlev selectivity index and a compositional analysis. In addition, we determined the effect of different habitat variables (dominant vegetation, vegetation height, cover and site) on the presence of the species fitting a binomial GLM with logistic linking function. We found that the Sardinian Warbler ( Curruca Melanocephala) selected scrub-dominated areas; while the Dartford Warbler ( C. undata) preferred areas with low (<50%) vegetation cover; and the Subalpine Warbler ( C. cantillans) was present in areas with scrubs and low (<50%) vegetation cover, avoiding crops. The compositional analysis showed that the species used different vegetation types, in relation to their availability and that the selection differed between species. The Sardinian Warbler was the only species which showed spatial variation in reproductive habitat selection. Our results evidence that the studied warbler species select and avoid different types of vegetation in relation to their specific requirements and the present habitat structure. This represents valuable information to understand the composition of local communities and the reproductive habitat selection of the studied species.

Foraging behavior of Raramuri Criollo vs. Angus cattle grazing California Chaparral and Colorado Plateau shrublands

Selecting livestock genetics adapted to arid environments, such as Criollo cattle, is one of several strategies recommended for decreasing the vulnerability to climate change of ranching in the southwestern USA. Our objective was to determine whether desirable foraging traits of Criollo cattle previously documented in the Chihuahuan Desert, held true in two of the most climate-vulnerable ecosystems of the Southwest. We conducted a study at Rancho Corta Madera (RCM) in southern California and Dugout Ranch (DR) in southeast Utah. Twenty mature cows, 10 Raramuri Criollo and 10 Red or Black Angus, were monitored with GPS collars during multiple seasons between 2018 and 2021. Geolocation data were used to compute daily distance traveled (km*d−1), movement velocity (m*min−1), path sinuosity (SI), time spent grazing, resting, or traveling (h*d−1), and area of the pasture explored (ha*d−1) as well as to calculate selection of vegetation cover types (E, Ivlev's Electivity Index) by cows of each breed. The effects of breed, season, year, and pasture on each of these metrics were modeled with repeated measures analyses of variance. At both ranches, statistically detectable differences (P ≤ 0.05) between breeds were observed for most behavior metrics during the dormant season. Conversely, few breed differences were observed during the growing season. Criollo cattle exhibited greater relative preference for a number of shrub dominated vegetation types at both ranches, and similar relative selection of grassland dominated sites compared to Angus counterparts. At both ranches, Criollo cattle exhibited similar or less relative preference for riparian areas vs. Angus counterparts. Breed divergence vs. convergence of foraging behaviors during the dormant vs. growing seasons, previously observed in the Chihuahuan Desert, was documented at both sites. Positive system outcomes associated with foraging traits of Criollo cattle could be expected to occur more broadly across the Southwest.

Wildlife habitat mapping using Sentinel-2 imagery of Mehao Wildlife Sanctuary, Arunachal Pradesh, India

Mehao Wildlife Sanctuary, situated in the state of Arunachal Pradesh, is part of an important biodiversity hotspot in the north-eastern part of India in the Himalayas. The current study deals with the identification of important wildlife habitats in the sanctuary. We used a supervised classification technique to delineate these habitats in the sanctuary, which are used by several mammals and bird species encountered during camera trap and sign surveys conducted between November 2017 and May 2020. Satellite images from Sentinel – 2A were used to classify the land use land cover (LULC) of the sanctuary. The LULC information was generated by using a maximum likelihood classifier. We classified a total of thirteen LULC classes, i.e., water, built-up, agriculture, orchard, grassland, bamboo forest, bamboo-mixed forest, riverbed, barren land, snow, wild banana, riverine forest and mixed forest. LULC classification reveals a high percentage of mixed forest, about 69.9%, followed by wild bananas at 7.2%. The commission and omission error rates, however, are high for riverbed and agriculture (0.5) and bamboo forest (0.5), respectively. The accuracy assessment showed an overall classification accuracy of 88.5% with a Kappa coefficient of 0.87. The abundance of mammals was high in the mixed forest, but Ivlev's electivity index shows that species generally avoided this habitat and preferred specialized forest habitats, such as bamboo forest, bamboo-mixed forest, grassland, riverbed and riverine forest. Our LULC map will provide a baseline for potential planning and monitoring changes of wildlife habitats in Mehao WLS.

Diet Electivity and Preferences for Food Resources in Chiasmocleis leucosticta (Anura: Microhylidae)

Predator–prey interactions are complex relationships between both participants. Although many food items are available in the environment for a frog, it can choose to feed on one item instead of another, depending on several aspects of the prey, such as size, availability, abundance, mobility, and palatability. In this study we compared the frequency of each food item we observed in stomachs of the frog Chiasmocleis leucosticta with the availability of leaf litter arthropods we collected at the same place and time that of the frogs through Ivlev's electivity index. We verified that the electivity for ants and mites as food items in the diet of the population from Reserva Florestal de Morro Grande is an actual preference. Chiasmocleis leucosticta seems to elect smaller sized genera, such as Solenopsis and Pheidole, and avoid bigger and more aggressive ants, such as Pachycondyla, Camponotus, and Odontomachus. Also, we suggest that for C. leucosticta or even for other Microhylidae there is reason to believe that alkaloids are obtained as part of the diet; related studies on the biochemistry of this family, genus, and species are encouraged.

Spotted hyaena Crocuta crocuta feeding ecology and selectivity of large herbivorous prey in the Namib desert.

We have investigated the relationship between spotted hyaenas in the south Namib Desert and large herbivorous prey and have summarized an updated overview of predator‐prey relationships in this resource‐limited arid environment. Over the 52‐month study, we recorded the densities (#/km−2, ±SE) of the four local large herbivorous prey species: gemsbok (1.229, ±0.50), springbok (1.352, ±0.48), ostrich (0.648, ±0.23), and greater kudu (0.343, ±0.00). A fecal analysis was performed on 146 collected spotted hyaena scats, and prey items were identified and hairs cross‐follicle analyzed to the species level. Spotted hyaena diet at the study area remained opportunistic with 240 identified prey items representing eight differing prey species being recorded, ranging from ostrich eggs to large ungulates. The Ivlev's Electivity Index was used to determine which large herbivorous prey was most selected for. Although gemsbok had a higher representation of prey items in the sampled scats, all sampled large herbivorous prey species scored below 0 and are thus generally avoided in relation to their availability in the environment. If any prey preferences are expressed by spotted hyaena in the Namib, it can be presumed to be a nonsampled prey species. We therefore promote further detailed investigations into all other prey species present, and seasonal variations of prey densities and scat sampling, within the study environment.

Dietary ecology of Markhor(Capra falconeri cashmiriensis) in winter range of Kazinag National Park, Kashmir, J&K, India

Background/Objective: Understanding winter diet composition of wild ungulates in temperate habitats is of paramount importance for devising conservation measures. The winter diet composition of Markhor (Capra falconeri), one of the least studied ungulate species, was assessed in Kazinag National Park (KNP) of Jammu and Kashmir, India. Methods: Reference slides of 15 available plant species, through micro-histological technique were prepared. Tests like Diet Selection Values (DSV), Ivlev\'s Electivity Index (IEI) and Chi-square tests were applied to study the selection and preference of dietary items. Findings: 80 fecal samples of markhor were analyzed in winter seasons of 2017 & 2018, and compared with reference slides to evaluate the winter diet. Fifteen (15) plant species belonging to 7 families were identified in the diet. Use of Ivlev\'s Electivity Index (IEI), revealed that, shrubs were strongly preferred during this season, besides one graminoid species (Poa pratensis). Among the most preferred species are, Poa pratensis (DSV=6.17) followed by Prunus tomentosa (DSV=2.42), Indigofera heterantha (DSV=2.23), Lonicera spp. (DSV=1.66) and Euonymus hamiltonianus (DSV=1.63). Chi-square goodness of fit test showed that markhor did not feed on all plant species uniformly (p< 0.05). Novelty: Our findings infer that, markhor shows feeding flexibility to adapt to change in forage availability. We recommend that plant species which are the major components of diet of markhor during resource- lean winter be conserved and propagated on priority. Keywords: Diet composition; fecal analysis; Kazinag National Park; markhor; winter

Decline of zooplankton food resources of Limnothrissa miodon fishery in Lake Kariba: Global warming‐induced ecosystem disruption by Cylindrospermopsis raciborskii

AbstractThe present study was conducted on the Lake Kariba portion of the Middle Zambezi Biosphere Reserve. Magadza (2011) previously reported the pelagic Lake Tanganyika sardine (Limnothrissa miodon) fishery introduced into Lake Kariba was declining. This phenomenon was attributed to observed climate‐change‐related warming of the lake, facilitating establishment of the invasive Cylindrospermopsis raciborskii, currently the dominant alga in the lake. Chlorophyceae contribute to less than 10% of the phytoplankton biomass. Accordingly, it was postulated that its dominance in the lake resulted in a food chain disruption because this cyanobacterium was not preferred by zooplankton grazers. Accordingly, the present study examined the feeding behaviour of L miodon with reference to available food items in the Sanyati Basin of Lake Kariba. The results highlighted a virtual absence of entomostraca zooplankton in the Sanyati Basin of Lake Kariba, in contrast to previous findings of previous studies, the avoidance of C. raciborskii in the diet of L. miodon, as measured by the Ivlev electivity index, a low stomach fullness index, the movement of L. miodon to macroinvertebrates associated with the littoral zone as a food source, and unfavourable dietary indicators of L. miodon. These results collectively suggest a food deficit for L. miodon in Lake Kariba, leading to the previously observed decline in the lake fishery.

We Ain't Afraid of No Ghosts: Tracking Habitat Interactions and Movement Dynamics of Ghost Tags under Differing Flow Conditions in a Sand‐Bed River

AbstractThe use of PIT tags has rapidly proliferated since their introduction, and new mobile detection methods have been developed. However, the presence of ghost tags (i.e., PIT tags left in the system after a fish dies) creates uncertainty about the status (live or dead) of tags detected. Herein, we describe our raft‐based mobile PIT tag antenna system, which was used to evaluate the movements of “seeded tags” (i.e., PIT tags that we placed in the river as ghost tag analogs) and their interactions with habitat features. We deployed 5,000 seeded tags in the San Juan River, a large sand‐bed river in the southwestern USA. Total distances moved by PIT tags ranged from 0.8 to 4,124 m, but 75% of movements were less than 100 m. Flow conditions causing the smallest to largest movements were (1) base flows, (2) spring runoff flows, (3) flash flood flows, and (4) a combination of spring runoff and flash flood flows. Based on Ivlev's electivity index, tags were more likely to be detected in riffles than in runs. These findings will help to classify mobile PIT tag detections as ghost tags or live fish, a critical data gap limiting the accurate estimation of demographic rates, population status metrics, and descriptions of the habitat use of fishes.

Plant community structure of the floating meadows of a hypereutrophic wetland in the Indo-Burma Biodiversity Hotspot

Floating meadows are widespread globally, but ecological information on their vegetation structure and functions is lacking. We examined the structure and composition of the vegetation of the floating meadows of Keibul Lamjao National Park, Manipur, located in the Indo-Burma Biodiversity Hotspot. The floating meadows in the park are crucial for the survival of the globally threatened Eld’s deer (Rucervus eldii) and the hog deer (Axis porcinus). Vegetation data were collected from 936 plots of size 0.5 m × 0.5 m during winter and summer. The vegetation data were analyzed using two-way indicator species analysis (TWINSPAN) with PC-ORD version 4.20. Nine plant communities were observed in summer and eight in winter, with two communities being common to the two seasons. The overall Shannon and Simpson diversity indices, species richness and evenness of the communities varied significantly between summer and winter. The evenness (0.713) and diversity (H′, 1.335) indices in summer indicate high species diversity, which is mainly due to homogenous distribution of the species. The Ivlev Electivity Index (IVI) indicates that plant communities have a specific preference for meadow thickness, i.e., communities that prefer thick meadows avoid thin meadows. Competition among plant communities in terms of moisture and nutrient availability appears to be low due to the hypereutrophic condition of the lake and the floating nature of the meadows. But Capillipedium spp., Phragmites karka, Leersia hexandra and Zizania latifolia appear to exhibit monodominance, as indicated by their frequency and abundance in most of the communities. Protection of areas with thick meadow from further deterioration is crucial for the long-term conservation of the Eld’s deer and associated wild ungulates.

Diet selectivity in a terrestrial forest invertebrate, the Auckland tree wētā, across three habitat zones.

Insects are important but overlooked components of forest ecosystems in New Zealand. For many insect species, information on foraging patterns and trophic relationships is lacking. We examined diet composition and selectivity in a large‐bodied insect, the Auckland tree wētā Hemideina thoracica, in three habitat zones in a lowland New Zealand forest. We asked whether H. thoracica selectively forage from available plant food sources, and whether these choices were lipid‐rich compared to nonpreferred available plants. We also identified the proportion of invertebrates in their frass as a proxy for omnivory. From reconnaissance plot sampling, together with fecal fragment analysis, we report that more than 93% of individual tree wētā had eaten invertebrates before capture. Additionally, wētā in the highest elevation hillslope habitat zone consumed significantly fewer species of plants on average than wētā on the low‐elevation terrace habitat. Upper hillslope wētā also had the highest average number of invertebrate fragments in their frass, significantly more than wētā in the low‐elevation terrace habitat zone. Wētā showed high variability in the consumption of fruit and seeds across all habitat zones. Generally, we did not observe diet differences between the sexes (although it appears that male wētā in the mid‐hillslope habitat ate fruits and seeds more voraciously than females), suggesting that the sexes have similar niche breadths and display similar degrees of omnivorous behavior. Extraction of leaf lipids demonstrated a range of lipid content values in available plants, and Ivlev's Electivity Index indicated that plant species which demonstrated high electivity tended to have higher concentrations of lipids in their leaves. Our findings indicate that H. thoracica forage omnivorously and selectively, and hence play multiple roles in native ecosystems and food webs.

Trophic ecology of green turtleChelonia mydasjuveniles in the Colombian Pacific

Gorgona National Park (GNP) protects the only known feeding aggregation of juvenile green turtlesChelonia mydason the Pacific coast of Colombia. This study was undertaken to compare the diet of the two knownC. mydasmorphotypes (black and yellow), and to determine availability, selectivity, and quality of food resources at GNP. Oesophageal lavages and isotopic analysis of epidermal tissue were performed on turtles captured between February and December 2012. Food quantity was estimated by determining per cent cover in quadrats randomly placed on the reefs. Food quality of algae species was estimated by proximate analysis. Food selection was estimated using Ivlev's electivity index, and the trophic level of sea turtles at GNP was calculated. A total of 30 black (mean = 63.9 cm SCL) and 47 yellow (mean = 54.3 cm SCL) morphotype turtles were lavaged. Eight invertebrate and nine algae food items were identified in oesophageal contents. The most frequently found and abundant items in lavages were terrestrial plants, plastic fibres, invertebrates and algae. A total of 27 items, including 15 algae species, were identified on the reefs, of whichCladophorasp. was selected by black turtles, andHypnea pannosaandDictyotasp. were selected by both morphotypes; the latter species had the highest protein and lipid content, and low lignin content. A trophic level of 3.5 for black and 3.4 for yellow turtles was calculated. No significant difference in diet between the two morphotypes could be determined through lavage or isotopic analysis.

Spring habitat use by stocked one year old European sturgeon Acipenser sturio in the freshwater-oligohaline area of the Gironde estuary

Post release habitat selection was studied on forty eight 10-month-old hatchery reared European sturgeon (mean fork length 31.0 cm ± 3.0) in the tidal part of their native catchment using acoustic telemetry. Most of the fish reached the oligohaline estuary within 2–4 days (70 km downstream the release site). Seventy four percent of the fish migrated rapidly downstream of the estuary into mesohaline waters while 26% selected habitat in the freshwater/oligohaline part of the estuary based on their linearity and residency indices. We focused on individual habitat use of these fish. The home range size (HR) was calculated using two methods: the kernel utilization distribution (KUD) which is driven by the maximum detection location density, and the Brownian Bridge (BB) approach which allows the time component of the trajectory path to be taken into account. The average 50% HR KUD was 5.6 ± 2.7 km2 (range 1.1–10.3 km2) and it was estimated to be 6 times larger using the 50% HR BB method (average reaching 31.9 ± 20.7 km2, range 5.2–77.8 km2). Habitat characterization (available prey, substrate and depth) in the studied area was described and the Ivlev electivity index was calculated using the habitat within the 50% HR BB for each individual. Despite the spatial use of different core areas among the fish tagged, we observed a convergence in habitat preference. For substrates, sturgeons showed avoidance of gravel and large rocks as well as fine and medium gravel. There was a significant preference for sand, silts and clay. For depth, they exhibited a preference firstly for the 5–8 m depth range and secondly for the 2–5 m range, a strong avoidance of depth range 8–20 m and a slight avoidance of shallow (0–2 m) and intertidal areas. For prey, individual variability was high. The most homogenous results were found for annelid polychaeta, with a slight preference for areas with this group of preys which are abundant in the saline estuary. For some individuals, a preference for areas with crustacea or nematodea and avoidance for areas with mollusks, insects or oligochaeta occured. We explain our results in light of foraging behavior and adaptation to the wild environment after captivity.For sturgeon population restoration projects in western Europe, these habitat preferences are key-features needed to evaluate the essential habitat availability for A. sturio juveniles in the tidal area at the front of the freshwater/saline transition waters.

Seasonal profile of the diet of the dace Telestes karsticus Marčić &amp; Mrakovčić, 2011 (Cyprinidae, Leuciscinae) endemic to Sušik Creek, Croatia

The first data on the feeding ecology of the endemic Telestes karsticus are presented for specimens sampled monthly (July 2007–July 2008) from the Sušik Creek in the Lug Polje field, Croatia. Macrozoobenthos density was calculated and compared with the stomach contents of T. karsticus and the seasonal profile of the diet was examined. The ratio of gut length vs. standard length was 0.9 ± 0.12. Gut contents revealed that benthic invertebrates accounted for the majority of food consumed, although terrestrial arthropods, plant material, algae and fish were also found. Since this is the only fish species in the investigated creek, T. karsticus can be concluded to be cannibalistic. The proportion of empty guts found in all seasons was small, indicating year round feeding. The number and diversity of prey species was highest in spring and lowest in summer. Ivlev's electivity index was very high for Cladocera, Coleoptera, Trichoptera, Heteroptera and Hymenoptera in all seasons, suggesting positive selection for these prey groups, as opposed to Oligochaeta, Isopoda and Bivalva, which showed negative values in all seasons. For Actinopterygii, the Ivlev coefficient of selection was highly negative in spring, and highly positive in summer. Plant matter was detected in stomach contents in all seasons, with the highest share found in summer when other prey species were less available. The karstic dace is a generalised feeder, consuming the most available prey, and therefore can be classified as a euryphagous omnivore.

Ecología trófica del “sapo cuerno” (Ceratophrys calcarata, Boulenger 1890) (Anura: Ceratophryidae), en La Avianca, Magdalena, Colombia

Objective : To establish the trophic ecology Ceratophrys calcarata , the type of prey, their amount and relative importance of their diet. Methodology : By analyzing the stomach contents of 64 specimens of C. calcarata diet in the districts of La Avianca, Pivijay municipality, department of Magdalena he was studied; from June to November 2011 on three sectors for two days each month, with a time intensity town six hours, that is, within two days the towns will be scrolled. Data were analyzed by sex, plus the abundance of other species of frogs associated with habitat “Horn toad” was evaluated as a potential food; dams were classi ed at the level of order and species. Results : A total of 92 food components were classi ed into nine categories, being the most relevant Anura group according to the relative importance index is found; trophic niche breadth measure Levins index was 0.44, categorizing the species as intermediate between generalist and specialist habits, comparing the diet of males and females through the square test of Hotelling, states that no there are signi cant differences (p=0.069); Jaccard index showed the similarity between the sexes with a value of 0.63, the Ivlev selectivity index showed that species of frogs, Rhinella granulosa and Pleurodema brachyops more dams were ingested by C. calcarata . Conclusion : C. calcarata species feeds on a wide variety of prey.

Can behaviour buffer the impacts of climate change on an arid-zone bird?

Behavioural thermoregulation, particularly the use of cool microclimates, is one method by which organisms could avoid the worst effects of climate warming. However, retreat into cool microsites, e.g. shady vegetation or burrows, may carry important lost-opportunity costs. These could include reduced opportunity for foraging, breeding or territorial defence, each carrying implications for fitness. We investigated patterns of microclimate use and foraging behaviour by Southern Fiscals Lanius collaris in the Kalahari. We used Ivlev's electivity index to assess preference of breeding males for perch types with different thermal properties. We found that Southern Fiscals preferred to hunt from high, sunny perches at all times, except on hot afternoons (air temperature >35 °C), when they switched their preference to high, shaded perches. Black-bulb thermometers indicated shaded perches were always cooler than sunny perches, especially on hot afternoons. Therefore, Southern Fiscals could reduce thermoregulatory costs by switching foraging locations. However, Southern Fiscal foraging success rates were highest when hunting from sunny perches, and were reduced by c. 50% when hunting from shaded perches. Our data suggest that Southern Fiscals were making a trade-off on hot afternoons, compromising foraging intake in return for thermal benefits. We discuss potential costs and consequences of this trade-off under climate change.

Indicators of movement and space use for two co-occurring invasive crayfish species

Red swamp crayfish (Procambarus clarkii) and signal crayfish (Pacifastacus leniusculus) are two invasive freshwater species with a worldwide distribution. The objective of this work was to investigate how the two species move and use space in an area of recent coexistence. Simultaneously, we test the use of new tools and indices to describe their movement patterns. To accomplish this we performed a radio-tracking program within a river-type habitat during two different periods (September/October 2010 and June/July 2013). We used spatial analysis tools to map crayfish radio-location data with and without accounting for the curvature of the river. To assess the consistency of the direction of movement and of the distances traveled by crayfish, two indices were developed. To assess the habitat preferences of each species we applied Ivlev's Electivity Index and the Standardized Forage Ratio. Movement of P. clarkii and P. leniusculus differed. The average detected movement was 8.8mday−1 for P. clarkii and 17.5mday−1 for P. leniusculus. However, crayfish behavior ranged from almost complete immobility – sometimes during several days – to large movements, in half a day, up to a maximum of 255m for P. clarkii and 461m for P. leniusculus. The proportion of upstream or downstream movements was independent of the species and both species displayed no preference for either direction. The indices of consistency of movement showed a large interindividual variation. Species and period (2010 or 2013) affected the mean daily distance traveled, maximum observed distance from location of release and percentage of observations under vegetation cover. The Ivlev's Electivity Index and the Standardized Forage Ratio presented similar results. P. clarkii showed a preference for pool areas with riparian vegetation cover while P. leniusculus preferred riffle and pool areas with riparian vegetation cover. Our work provided new and valuable data for modeling the active dispersal of these two problematic invaders in a context of coexistence.

A cat among the dogs: leopardPanthera pardusdiet in a human-dominated landscape in western Maharashtra, India

AbstractThe ecology and predator–prey dynamics of large felids in the tropics have largely been studied in natural systems where wild ungulates constitute the majority of the prey base. However, human-dominated landscapes can be rich in potential prey for large carnivores because of the high density of domestic animals, especially in tropical countries where pastoralism is an important livelihood activity. We report the almost complete dependence of leopardsPanthera parduson domestic animals as prey in the crop lands of Ahmednagar district, Maharashtra, India. From analysis of 85 confirmed leopard scats, 87% of the leopard's prey biomass consisted of domestic animals, with 39% consisting of domestic dogsCanis lupus familiarisalone. The only wild species that occurred in the leopard's diet were rodents, small indian civetViverricula indica, bonnet macaqueMacaca radiataand other primatesSemnopithecusspp., mongooseHerpestesspp., and birds. Interviews conducted in 77 households distributed randomly in the study area documented a high density of domestic animals: adult cattleBos taurus, calves, goatsCapra aegagrus, dogs and catsFelis catusoccurred at densities of 169, 54, 174, 24 and 61 per km2, respectively. Ivlev's electivity index indicated that dogs and cats were over-represented in the leopard's diet, given the higher densities of goats and cattle. The standing biomass of dogs and cats alone was sufficient to sustain the high density of carnivores at the study site. Our results show that the abundance of potential domestic prey biomass present in human-use areas supports a relatively high density of predators, although this interaction could result in conflict with humans.

Incidental catch of marine turtles by Spanish bottom trawlers in the western Mediterranean

Abstract A questionnaire‐based survey of fishermen was conducted in the Valencia region (eastern Spain) to assess the levels of marine turtle bycatch. Interviews covered 41.3% of the bottom trawling fleet in the region and included 111 fishermen (one per boat). Results were combined with those from previous studies conducted in neighbouring regions using the same methodology to assess the global impact of bottom trawling on the western Mediterranean stock of the loggerhead turtle (Caretta caretta). Estimated turtle catch per unit effort (CPUE) is 0.09 turtles per vessel per month, according to the information reported by fishermen. As a consequence, the whole fleet of bottom trawlers operating off the Valencia region was involved annually in 238 turtle bycatch events (95%, CI: 173–304). Ivlev's electivity index revealed that bottom trawling bycatch was higher than expected according to fishing effort in the northern part of the study area, where the continental shelf widens. The fishermen's perception was that the local stock of loggerhead turtles is declining, and that drifting longlines and bottom trawling are, at least in part, responsible for this trend. According to previous studies as well as the current results, bottom trawlers operating off mainland Spain capture mainly loggerhead turtles from the rookeries in the eastern Mediterranean, with only a low percentage of turtles of Atlantic origin. Loggerhead turtle bycatch by bottom trawling deserves more attention in the Valencia region, particularly in its northern part. Conservation measures in the area are discussed. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Selective behavior of Creole goats in response to the functional heterogeneity of native forage species in the central Monte desert, Argentina

The changes in forage availability and the physicochemical variability of plants influence the diet selection by herbivores. In this study, the foraging behavior of Creole goats was studied in terms of botanical composition of the diet, food availability and physicochemical properties of vegetation. The study was performed in a desert rangeland in the northeast (NE) Mendoza region in Argentina. Experiments with grazing goats were made in dry (winter) and wet (summer) seasons and cafeteria experiments (feeding trial) were performed during the summer. Food availability was estimated from forage species cover. Botanical composition of the goat's diet was determined by microhistological analysis of fecal samples. Morphological parts of forage species consumed by goats were sampled and analyzed to determine chemical traits (plant nutrients and secondary metabolites) in both seasons. Also, during summer, the two morphological traits of browse species stem specific density (SSD) and specific leaf area (SLA) were evaluated. In the experiments with grazing goats, diet selection was evaluated based on Ivlev's electivity index (Iˆ) and, in cafeteria experiments, preference was estimated based on the number of bites. Diet selection varied between the two seasons. Grazing goats showed differences in the patterns of diet selection related to changes in forage availability. The botanical composition of the diet had a greater (p<0.001) participation of woody species in relation to grass species in both seasons, but the herbaceous stratum was more utilized by goats during the summer according to their higher availability. Correlations between diet and availability were positive in both seasons, but not significant in summer. The models including crude protein (CP), neutral detergent fiber (NDF) and total phenols (TP) had substantial support for predicting variation in diet selection in summer and winter. In both seasons the preference increased as the concentrations of CP, NDF and TP increased, but the effect of CP was significant only in winter. Thus, goats selected supplementary food mixtures (mixed diet) and tannins were not considered dissuasive but, rather, were maintained below a certain threshold. In summer, SSD was negatively and significantly related to diet selection by grazing goats. This morphological trait allowed explaining a greater percentage of the variation in Iˆ (36%) with regard to the variation explained by the chemical variables (16%). In cafeteria experiments, in summer, the optimization of nutrient intake rate through consumption of species with low SSD values represented a best explanation for the preferences observed, whereas the hypotheses of minimization of secondary metabolites and maximization of nutrients were not able to fully explain the preferences observed in cafeteria experiments. To conclude, dietary decisions by goats in desert rangelands could be interpreted in terms of intake rate optimization and complementation of nutrients and secondary compounds, rather than by explanations involving the isolated effects of nutrient intake maximization or tannin intake minimization.

Habitat use by Astyanax taeniatus (Jenyns, 1842) (Characiformes: Characidae) in a coastal stream from Southeast Brazil

The habitat use of a stream-dwelling Astyanax taeniatus from the State of Rio de Janeiro was investigated. We performed 12 h of underwater observation in a 200 m long stretch in the upper Roncador stream and quantified the following microhabitat descriptors: (i) water velocity, (ii) distance from the stream bank, (iii) substratum, and (iv) water column depth. Microhabitat selectivity was analyzed by comparing the microhabitat used by fish and the microhabitat available in the study site as well as by applying the Ivlev Electivity Index to the microhabitat use data. Differences in the use and availability of the various microhabitats revealed non-stochastic patterns of spatial occupation by A. taeniatus, which was selective for two of the four analyzed microhabitats. Our findings indicated that A. taeniatusis associated with habitats that have higher depths, low water velocity, and sand and bedrock substratum.