Abundance Of Potential Prey Research Articles

Forest Tent Caterpillar Outbreaks Drive Change in Ant Communities in Boreal Forests

Insect outbreaks are major drivers of natural disturbances in forest ecosystems. Outbreaks can have both direct and indirect effects on the composition of soil arthropod communities through canopy opening, nutrient addition and predator-prey interactions. In this study, we aimed to understand the effects of forest tent caterpillar (Malacosoma disstria; FTC) outbreaks through cascading effects on ant communities in both temperate and boreal forests in Canada. Pitfall traps and Berlese funnels were used to compare the ant communities, as well as the surrounding arthropod communities, between control and outbreak sites in boreal and temperate forests (in Quebec, Canada). Using the Sørensen dissimilarity index, we determined the alpha and beta diversity of the ant community. Other arthropods collected in the traps were counted to evaluate the richness and abundance of potential prey for the ants and other potential predators of the FTC. We used an indicator species analysis to examine the species associated with sites defoliated by the outbreak. In the boreal forest, we found that FTC outbreaks caused decreases in species richness and increases in the evenness of ant communities in defoliated sites. In the boreal forest sites, species composition varied significantly between control and outbreak sites. This pattern was driven in part by the presence of other predators. A similar, but weaker pattern was observed in the temperate forest. We saw no changes in the beta diversity in the boreal forest, but did see a significant decrease in the temperate forest between the outbreak sites and the control sites. Ant species in the boreal forest tended to exhibit a more marked preference for either control or previously defoliated sites than species in the temperate forest. Our study showed that disturbances such as insect outbreaks can drive changes in the ant community. While we saw small effects of outbreaks, manipulation experiments using resource addition could help us validate the mechanisms behind these relationships.

The effects of river regulation on diet diversity, dietary niche overlap and foraging habitat preferences of two sympatric plover species

During migration waders use a variety of microhabitats and a wide range of prey to supply their nutritional requirements. Most of them form multispecies flocks, which may result in increased competition for resources. In this study, we compare the abundance of potential prey for Ringed and Little Ringed plovers at unregulated and regulated stretches of the Vistula River. We also observed plovers and assigned them to the habitat in which they foraged and compare the diet, dietary niche overlap and foraging habitat preferences of these two plover species. The larger species, the Ringed Plover, foraged more often in invertebrate abundant habitats, yet exclusively on the three most abundant prey species, while the smaller species expanded its diet to include invertebrate species of low abundance and in suboptimal habitats. In the regulated river section, below the dam, the diet of the Little Ringed Plover was more diverse, and the dissimilarity of both plovers’ diets was much higher than in the regulated section. The unregulated river section offered richer foraging grounds and both species showed similar proportions of primary prey items in their diets here resulting in greater dietary niche overlap and weaker resource partitioning. Our study shows that river regulation increases competition for food resources due to a lower abundance of potential prey and has an influence on diet diversity and foraging habitat preferences of smaller, less competitive plover species.

Relative abundance, habitat selection, and diet of the coyote in northern México

The coyote (Canis latrans) is a widespread predator with a high degree of adaptation to different ecosystems. The objective of this study was to estimate the relative abundance index, habitat selection, and diet of C. latrans through scent stations, in two types of vegetation located in northwestern Chihuahua. From April 2018 to March 2019, ten fixed scent stations (SS) were placed in pine-oak forest and other ten in semi-open grassland, with a linear separation of 500 meters between each station to achieve a five km transect in each vegetation during 12 samplings (two sampling night per month) for totaling 420 SS after discarding inactive SS. The relative abundance index of coyote showed that both types of vegetation, pine-oak forest (0.30) and semi-open grassland (0.23) were used in a similar way. The habitat selection test (Chi2) showed that coyote abundance and type of vegetation were independent (χ2 = 2.96, P > 0.05), not showing statistically significant differences in annual relative abundance index of coyotes between the two vegetation types. The food items detected in thirty-four scats collected belonged to mammals (55.9 %), fruits (35.3 %) and arthropods (8.8 %). Rodents and lagomorphs were the main source of food. Throughout the sampling period, the pine-oak forest showed the greatest relative abundance index of C. latrans. This may be because the forest provides them with shelter from climatic situations and a greater variety of seeds, fruits and insects. In this study the two seasons with the highest relative abundance were spring and autumn in both ecosystems, coinciding with an increase in rainfall, resulting in an abundance of potential prey (rodents and lagomorphs), and other food items like fruits. Regarding annual diet the most consumed prey were mammals. We found differences in diet between seasons, that can be explained by the variation in food availability among seasons.

Grey wolf feeding habits and their geographical variation in Northwest Spain

This study investigates wolf (Canis lupus) dietary preferences and their geographical variation by calculating frequency of occurrence and biomass consumption in three areas in the north-western Iberian Peninsula that differ in terms of the type and abundance of potential prey. Wolf dietary preferences were expected to be related to the availability of a species of free-roaming horses (Equus ferus atlanticus) and much less to traditional livestock in each habitat.The diet of wolves was found to comprise mostly Galician feral horses when available, with a low proportion of livestock. The next most consumed species were wild boar (Sus scrofa) and cattle (Bos taurus taurus). A much higher consumption of traditional livestock (84% biomass) was observed in the one study area where there were no feral horses.The fact that access to feral horses may help decrease wolf predation on other species of livestock which are more economically important and the environmental benefits of horses in protecting against forest fires suggest that conservation and expansion of this endangered species of horses should be encouraged. Strengthening existing populations and possibly re-introducing native wild species within the wolf's range may be the most environmentally friendly way to reduce economic losses for farmers and cattle breeders.

Comparison of the Relative Abundance of Potential Prey to the Diet of the Louisiana Pine Snake (Pituophis ruthveni)

Pituophis ruthveni (Louisiana Pine Snake) occurs in parts of western Louisiana and eastern Texas and was recently listed as a threatened species under the Endangered Species Act. It is considered a diet specialist because it mostly feeds upon Geomys breviceps (Baird's Pocket Gopher), which make up ∼75% of its estimated total prey biomass. Diet specialization is rare among vertebrates. One factor that can influence dietary diversity is the availability and abundance of prey items. To gain more insight on the Louisiana Pine Snake's diet, we sampled terrestrial and subterranean small mammals across 3 study sites within the range of this snake species in Louisiana to determine their relative abundance and availability. We compared these results to diet studies of the Louisiana Pine Snake to determine if any small mammal species were consumed more often than expected. The total of 59 small mammals captured consisted of Baird's Pocket Gopher, Sigmodon hispidus (Hispid Cotton Rat), Peromyscus spp. (deer mice), and Reithrodontomys spp. (harvest mice). Baird's Pocket Gopher had significantly higher relative abundances and biomass than terrestrial small mammals. When compared to proportions of actual consumed prey species, the Louisiana Pine Snake preyed upon Baird's Pocket Gopher significantly more than expected based on their availability in the environment. Finally, Chesson's prey selection index determined that the Louisiana Pine Snake positively selected Baird's Pocket Gopher, while the other species were either randomly or negatively selected. The results of this research provide some insight into the factors affecting the diet choices of the Louisiana Pine Snake.

Jaguars in the matrix: population, prey abundance and land-cover change in a fragmented landscape in western Mexico

AbstractHabitat fragmentation threatens biodiversity worldwide, particularly affecting large-bodied species that require vast territories and move across long distances, including most large felids. The jaguar Panthera onca has lost more than half of its habitat throughout its range and its subpopulations are becoming isolated, making them susceptible to local extinction. Knowledge about the status of its subpopulations in highly fragmented environments is lacking but urgently needed. Using camera traps during 2019–2020, we estimated number of individuals, age classes and sex ratio, occupancy, relative abundance and density of jaguars in Nayarit, western Mexico. We also determined the relative abundance of potential prey and estimated the land-cover change rate during 1999–2019, using GIS. We found that a resident subpopulation of five adult females, two adult males and one cub, at a high density (5.3 individuals/100 km2), is supported by at least 14 wild prey species. Natural habitat in the area is rapidly decreasing because of expanding agriculture and shrimp farming: agricultural areas increased from 39 to 50% and mangroves decreased from 35 to 26% of the study area over 20 years. The high jaguar population density and the diversity and relative abundance of remaining wild prey are remarkable, considering that natural habitat in the area is highly fragmented, shrinking rapidly and embedded in a matrix of human-dominated land-cover types. Effective conservation actions are needed urgently, including the protection of patches with native vegetation, reforestation to maintain connectivity between these patches, and the involvement of local communities.

Effects of prey abundance on carnivore populations in the Faragosa-Fura landscape of the Southern Rift Valley, Ethiopia

Understanding how prey abundance affects carnivore species' abundance in sites is critical for the conservation of both prey species and carnivore species. However, research on the effects of prey species on multiple carnivore species in a human dominated landscape in the Southern Rift Valley of Ethiopia is largely untested. Our central premise was that the abundance of carnivores varies with potential prey abundance in different sites. To test this, we divided the study area into 15 grid cells (2 km x 2 km) and installed a camera trap in each grid for four seasons between 2020 and 2021. The results showed a total of 400 photographs of eight carnivore species, of which white-tailed mongoose and common genet were the most common, while leopards were the rarest. Except for the leopard, the record frequencies of all species varied significantly between camera stations. The Shannon diversity index and evenness index of carnivores for the study area were 1.868 and 0.809, respectively. A total of 28 prey species were identified, of which 13 were birds and 15 were mammals. Overall, the record frequency of prey species was 801, of which 288 were birds and 513 were mammals. Primates and medium-sized ungulates were the most abundant species among prey groups. Medium ungulates and large birds both had a significant positive relationship with carnivore abundance, and they contributed to 76.92% of the carnivore abundance in sites. The community structure analysis showed African civet, common genet, leopard, spotted hyena and white-tailed mongoose were positively correlated with medium ungulates and large bird prey groups. A species-specific model showed the spotted hyena prefers areas with a high abundance of both large and medium ungulates, while the other species mainly prefer areas with medium ungulates and/or large birds. Our findings support the importance of prey groups' abundance for carnivore conservation in the human-dominated rural landscape of the Southern Rift Valley of Ethiopia • The effect of prey species abundance on carnivore populations in a human-dominated landscape are largely untested. • Carnivore abundance were assessed using camera trapping survey. • White-tailed mongoose and common genet were the most common, while leopard was the rarest. • Primates and medium-sized ungulates were the most abundant prey species.. • Medium ungulates and large birds were the most important predictors and contributing more for carnivore abundance in sites.

Factors influencing the abundance of wintering western snowy plovers at Crown Memorial State Beach

Survival during the nonbreeding season, when mortality from food shortages and raptor predation is highest, influences shorebird population growth. These selection pressures, as well as anthropogenic influences, can shape wintering shorebird habitat use patterns. The western snowy plover (Charadrius alexandrinus nivosus) is a small shorebird that uses sand-spits, dune-backed beaches, open areas around estuaries for foraging and roosting. The Pacific Coast population of western snowy plovers is listed as a federally threatened species and a California Species of Special Concern. Previous studies suggest humans, dogs and corvids are sources of disturbance to plovers on public beaches. During 2014 to 2019, these disturbance factors were examined at Robert W. Crown Memorial State Beach in Alameda, California. In decreasing order of impact, the beach using public, corvids, and dogs were found to be the major stressors to over wintering plovers. Both the public and corvids respectively, resulted in disturbance and avoidance behaviors by plovers nearly 40% of the time. In 2015, the District created the Plover Protection Zone (PPZ) by installing symbolic fencing, signage, and establishing a volunteer team to monitor plovers and educate the public. In 2016, the potential prey abundance within the plover protection zone and areas directly north and south were examined using core samples and sticky traps. Statistical analysis showed a significant difference in the amount of macro-invertebrate prey available in the area used by the plovers as compared to other locations. Habitat choice and prey availability are vital to wintering shorebird. During this study, the wintering population of western snowy plovers increased from six to over 54 individuals.

Diet composition and prey choice by the Great Grey Shrike Lanius excubitor during the non-breeding period: comparing two methods of diet analysis

ABSTRACT Capsule The diet of the Great Grey Shrike Lanius excubitor during the non-breeding period was assessed using analysis of pellets and larders. The two methods gave different results but together showed a preference for voles, crickets and dung beetles. Aims To describe the diet composition of the Great Grey Shrike based on analyses of the contents of pellets and larders; to compare the two methods, and to compare prey taken in relation to its local availability. Methods The research was carried out during the non-breeding period of the Great Grey Shrike in an agricultural landscape of east-central Poland in 2014–2018. The diet was assessed through the analysis of the contents of larders and regurgitated pellets. The abundance of potential prey was assessed with pitfall traps for invertebrates and live traps for small mammals. Results In larders, the ratio of vertebrates to invertebrates was 34.3 : 65.7 (n = 528 prey items), with Orthoptera, Coleoptera and Rodentia predominant. In pellets, the ratio was 64.6 : 35.4 (n = 237 prey items in 155 pellets), with Rodentia and Coleoptera being most numerous. The proportions of the most frequently found prey taxa differed significantly between the two methods of diet analysis. In relation to potential prey availability, Great Grey Shrikes showed a preference for Common Voles Microtus arvalis but seemed to avoid mice Apodemus spp. and Diptera. The greatest discrepancies between the methods were for Coleoptera, Lepidoptera and Orthoptera. Conclusion The results of the pellet and larder analyses differed, mainly because of the large number of Orthoptera found in the larders; shrikes can use them to mark their territories and so they may remain uneaten. Both analytical methods should be used simultaneously to determine the diet composition.

Population and individual trophic niche of two sympatric cobweb spiders, Nihonhimea tesselata and Tidarren haemorrhoidale (Araneae: Theridiidae)

Diet composition of spiders may depend on several factors, such as the relative abundance of potential prey, microhabitat selection, structure and physical properties of webs, adaptations to attract specific prey, among others. Variation in diet composition is probably highly influenced by individual's spatial distribution and web design. In this study, we evaluated the population trophic niche breadths of two sympatric cobweb spiders, Nihonhimea tesselata (Keyserling, 1884) and Tidarren haemorrhoidale (Bertkau, 1880) (Theridiidae). These species build distinct webs in an area of Eucalyptus monoculture in southeastern Brazil. We collected their prey and also recorded parameters of webs like a height from the ground, distance from tree trunks, and distribution across the Eucalyptus stand. The diet of the two species was highly distinct. However, diet similarity was not correlated with the distance between webs. There was also no spatial segregation between species within the forest stand. However, N. tesselata used more distal portion of Eucalyptus branches than T. haemorrhoidale, which usually attached several threads to the tree trunk. In addition, diet restriction of T. haemorrhoidale may also be determined by the use of gumfooted threads attached to tree trunks (predominantly capturing ants), while aerial webs constructed by N. tesselata are more efficient at intercepting several groups of flying insects. Together, these differences in microhabitat and web design allowed effective resource partitioning among these two dominant predators in the studied plantation forest.

Spatial niche partitioning among three small cetaceans in the eastern coastal area of Hokkaido, Japan

Spatial niche partitioning of marine mammals is thought to be caused by dietary differences. However, due to the difficulty involved with conducting simultaneous marine predator and prey distribution surveys at the same scale, marine mammals have not been studied alongside their prey distribution. To understand the spatial niche overlap between 3 small cetaceans observed in the eastern coastal waters of Hokkaido, Japan (Pacific white-sided dolphinLagenorhynchus obliquidens, Dall’s porpoisePhocoenoides dalli, and harbor porpoisePhocoena phocoena), and the mechanisms behind the differences in their distributions, visual and hydroacoustic surveys using a quantitative echosounder were concurrently conducted. A clear spatial niche overlap was observed between the Pacific white-sided dolphin and Dall’s porpoise, whereas the spatial overlap was moderate between the harbor porpoise and the other 2 species. In areas where Pacific white-sided dolphins were observed, potential prey was abundant in a shallower layer, at approximately 80-90 m depth. On the other hand, potential prey was more abundant in deeper layers in areas where Dall’s and harbor porpoises were observed. Water depth affected the potential prey abundance at all depth layers (0-300 m), as potential prey were more abundant in areas with a shallower water depth. Additionally, potential prey were more abundant in shallower layers (3-200 m) than in deeper layers (200-300 m), where the maximum water depth was 3000 m. The differences in spatial niche among Pacific white-sided dolphin, Dall’s porpoise, and harbor porpoise might cause their dietary differences, as they are epipelagic feeders, midwater feeders, and both epipelagic and midwater feeders, respectively.

Changes in landscape composition influence the abundance of insects on maize: The role of fruit orchards and alfalfa crops

The traditional agricultural landscape of Ebro Basin (NE Spain), which is mainly composed of alfalfa and cereal crops, has undergone changes in recent years, mainly consisting of an increase in the area occupied by intensively managed irrigated orchards. Recently, it has been reported that the presence of a higher proportion of orchards in the landscape and their management negatively affect the abundance and diversity of natural enemies. Two hypotheses are tested in this study: (1) the increased orchard surface has led to a reduction in natural enemies in neighbouring maize crops, and (2) the higher alfalfa proportion of agricultural land enhances the predatory fauna on maize. Maize fields were selected across a landscape gradient created by orchards and field crops (alfalfa and maize) in a buffer of 500 m. The abundance of 17 insect taxa in each maize field was estimated by means of 3 yellow sticky traps per season over three years. The insect abundance was related to the landscape structure (proportions of landscape elements and landscape diversity) and local variables (maize phenology, perimeter/area, weed diversity of the maize edges and abundance of the potential predators or potential prey). Our results show that the proportion of orchards in the landscape had negative effects on the main predators, and alfalfa had positive effects on herbivores and their predators. Semi-natural habitats (non-crop habitats and forest) and landscape diversity had low effects on insect abundance. However, variables at the local level included more significant effects than landscape structure; maize growth stages and abundance of potential prey or predators on the crop were the most influential variables at a local level. Here we show the interplay between different land uses types and local management and their impact on natural enemies and herbivores in maize crops in the Mediterranean area.

Habitat requirements of an arboreal Australian snake (Hoplocephalus bitorquatus) are influenced by hollow abundance in living trees

The value of tree hollows (cavities) to wildlife is well documented among birds and mammals, however few studies focus on their importance for snakes. Given increasing concern about the global net loss of hollow-bearing trees, it is imperative that studies extend to other vertebrate classes that may be dependent on this structural habitat component. We tested the hypothesis that habitat selection of an arboreal elapid, the pale-headed snake (Hoplocephalus bitorquatus), is primarily influenced by shelter requirements at multiple spatial scales. Consistent with our hypothesis, snake detection was biased towards a riparian ecosystem where hollow-bearing tree density was on average nine times greater than adjoining vegetation communities. In contrast, we found that the relative abundance of potential prey was equivalent among vegetation communities (frogs: P = 0.882; geckos: P = 0.306). At the microhabitat scale, snakes selected live hollow-bearing trees that were significantly larger (mean diameter: 74.5 cm ± 3.4, s.e.) than those otherwise available (42.4 ± 1.2 cm, s.e.) and estimated to be on average 111 years old. We recorded temperatures inside tree cavities to investigate whether the preference for live trees might be influenced by temperature buffering. Temperatures inside live trees were up to 16.4 °C below ambient in summer and 13.0 °C above ambient in winter. Temperature buffering was more pronounced in living trees (regression of cavity temperature against ambient, winter: r = −0.621; summer: r = −0.630) compared to dead trees (winter: r = −0.219; summer: r = −0.328), suggesting microhabitat selection may be driven by thermal requirements. Our study demonstrates the important role that mature, live hollow-bearing trees play in habitat selection by the pale-headed snake. It also suggests that the conservation of this species will be difficult in environments where such trees have been depleted due to land management practices. Managing forests for the persistence and recruitment of live hollow-bearing trees must be the primary conservation objective for threatened hollow-dependent fauna globally.

Using a recreational grade echosounder to quantify the potential prey field of coastal predators.

Quantifying the distribution of prey greatly improves models of habitat use by marine predators and can assist in determining threats to both predators and prey. Small epipelagic fishes are important prey for many predators yet their distribution is difficult to quantify due to extreme patchiness. This study explores the use of recreational grade echosounders (RGE) to quantify school characteristics of epipelagic fish and link their distribution to that of their predators at Banks Peninsula, New Zealand. The hydro-acoustic system was ground-truthed with 259 schools of epipelagic fish. During 2015 and 2016, 136 hydro-acoustic surveys were conducted with concurrent observations of Hector’s dolphin (Cephalorhynchus hectori) and little penguins (Eudyptula minor). The relative abundance of the two predator species during surveys was modelled according to the relative abundance of potential prey using generalised additive mixed models. Schools of epipelagic fish were readily detected by the RGE system and were more abundant in summer compared to winter. The models performed well, explaining 43% and 37% of the deviance in relative abundances of dolphins and penguins respectively. This is the first study to link the distribution of Hector’s dolphin to that of their epipelagic prey and confirms the utility of RGE in studies of habitat use in marine predators. Limitations associated with a lack of formal acoustic calibration and data formatting can be overcome and would make RGE valuable, inexpensive tools for investigating variability in populations of small pelagic fishes.

Comparison of wormlion behavior under man-made and natural shelters: urban wormlions more strongly prefer shaded, fine-sand microhabitats, construct larger pits and respond faster to prey.

Urban habitats differ from their natural surroundings in various aspects, such as a higher temperature and a distinct species composition. It is therefore not surprising that animal behavior too differs between these habitat types. We studied the foraging and habitat selection behavior of a pit-building predator, a wormlion, originating from either an urban or a more natural site. Wormlions occur in nature under structures that provide shelter from sunlight and rain, such as caves, and are also common in cities, occurring under artificial shelters. Wormlions construct pit-traps to hunt arthropods, and the pits constructed by urban wormlions were larger than those constructed by wormlions from caves. Urban wormlions responded faster to prey falling into their pit, probably leading to a higher capture success. We suggest that these 2 findings indicate the higher investment of urban wormlions in foraging, resulting from the higher abundance of potential prey in the city. Urban wormlions were choosier regarding their preferred microhabitat. While both fine sand and shaded microhabitats were preferred by wormlions, urban wormlions demonstrated a greater preference for such conditions. We suggest that relocation is more likely to lead wormlions in cities to find microhabitats of a higher quality compared with wormlions inhabiting caves. This is probably due to the larger areas in the city available for wormlions. Wormlions from the caves possessed more lipids, suggesting that they employ a conservative growth strategy, intended to contend with the uncertainty of prey arrival, in contrast to the city, where potential prey are more abundant.

Effectiveness of a mitigation measure for the lesser kestrel (Falco naumanni) in wind farms in Spain

Central-eastern Spain is characterised as being a flat and relatively open landscape, greatly used for agricultural purposes and with a high density of wind installations. This landscape also hosts a large population of the lesser kestrel (Falco naumanni), one of the species most threatened by collisions with wind turbines. During a ten-year period, we analysed bird mortality by recording deaths on three wind farms (WF), Cerro del Palo, Cerro Calderón and La Muela I, located in the province of Cuenca (Spain) and containing a total of 99 turbines. The aim of the study was to determine the variables associated with mortalities caused by these types of devices. Subsequently, the information obtained allowed a mitigation measure to be implemented for avoiding and minimising collisions. The procedure involved superficially tilling the soil around the base of turbines with a high collision rate. This measure was monitored for two years before and after implementation in order to compare its effectiveness, and involved making the areas around the turbines less attractive to kestrels by tilling and reducing the amount of vegetation and consequently the abundance of potential prey, mainly Orthoptera. If effective, the lack of prey would decrease the number of dead kestrels, as the birds of prey would need to search for food in other less dangerous areas (approximately 80 m away from the turbines). After monitoring the mitigation measure it was found that the number of collisions decreased by 75–100%. In fact, no collisions were registered during the two year period for all of the wind turbines with tilled surroundings. Based on these results it can be safely stated that this mitigation measure is an easy and inexpensive procedure that significantly and effectively reduces the number of kestrels that collide into wind turbines.

Patterns of habitat partitioning for the portunid crab Ovalipes trimaculatus in coastal Patagonian waters

Animals frequently face trade-offs between their requirements for maximizing growth and minimizing mortality risk. The partition of habitat use in foraging arenas and refuges as an answer to this trade-off has been evaluated in intertidal crabs but is poorly known in subtidal crabs. The subtidal crab Ovalipes trimaculatus lives and is captured by artisanal fishermen on sandy bottoms of the San Matías Gulf (Lat 41 °S; Argentina). Whereas these bottoms are poor in potential prey, the nearby rocky outcrops are much richer with relatively high abundance of potential prey for the species. Hence, we investigated if crabs in this area are using rocky bottoms as a foraging arena. Stomach content and stable isotopes analysis show that none of the evaluated prey (small teleosts, echinoderms, mollusks and crustaceans) contributed to more than 10% of O. trimaculatus diet, however prey from hard bottoms jointly contributed to 50–80% of the diet. Thus, O. trimaculatus is a generalist carnivore that, despite inhabiting mainly open sandy bottoms, uses rocky outcrops habitats as a foraging arena, probably due to their higher prey availability.

Feeding habits of the striped red mullet, Mullus surmuletus in the eastern Adriatic Sea

Feeding habits of the striped red mullet, Mullus surmutetus in the eastern Adriatic Sea were investigated. Stomach contents of 203 specimens (11.5 - 32.9 cm TL) collected by bottom trawling were analyzed. Commonly accepted procedures were followed during the diet composition inspection and standard keys were used for food items determination. Examinations showed that 39 identified prey taxa belong to 11 major systematic groups: Crustacea, Gastropoda, Bivalvia, Pisces, Cnidaria, Echinodermata, Polychaeta, Nematoda, Bryozoa, Algae and Rhizaria. The predominant and preferred prey category was decapod crustaceans within all size categories and only in the largest individuals, the dominance of Bivalvia followed by Polychaeta and Crustacea were found. The largest individuals also showed more variety in consumption of different prey categories and a higher mean number of prey items in comparison with smaller fish. No significant differences in prey foraging between males and females \((p>0.05)\) and regarding to season \((p>0.05)\) were found. Feeding on such wide spectra of prey without significant variations regarding to sex and season suggests that the striped red mullets are able to adapt to shifts in spatio-temporal variations in the abundance of potential prey. Presence of detritus in the digestive tracts is highly related to its foraging behaviour on muddy detritic bottoms.

Changes in spider diversity through the growth cycle of pine plantations in the semi-deciduous Atlantic forest: The role of prey availability and abiotic conditions

The replacement of native forests by tree plantations affects the diversity of biological communities, particularly in highly diverse tropical and subtropical ecosystems such as the semi-deciduous Atlantic forest. Previous studies in this ecosystem have focused on vertebrates, while only a few studies have been performed on the relationship between spiders and pine plantations. We aimed to estimate changes in spider richness and species composition over the course of a pine plantation forestry cycle of 15 years. We expected that the increase in environmental similarity (vegetation, prey availability) between native forest and tree plantations through the plantation growth cycle would promote its use by native spider species. We used six collection methods to characterize the spider assemblages and their potential prey in five replicates of native forest and pine plantations of three different ages representing the forest cycle (1–2, 5–6, 10–11 years old). Additionally, we described vegetation structure and recorded ground temperature and humidity during the sampling period. Analyses were carried out combining spiders from all sampling methods and independently on each vertical stratum. As expected, spider richness increased and the dissimilarity in relation to the native forest spider community decreased through the growth cycle of the pine plantation, associated with an increase in potential prey abundance and richness (but not vegetation structure). The response of spiders on each stratum showed interesting trends; opposite to the general pattern, in young plantations the ground strata exhibited a rich and distinctive spider assemblage while herbaceous strata showed similar diversity (richness and species composition) in all three plantation ages. Our results showed a rapid increase in spider richness in the first 6–7 years after plantation and a subsequent stabilization. Also, the proportion of native species in plantations increased from 6% in the first years to 34% and then remained constant until cutting age (11–12 years). Differences in species composition were mainly due to both differences in richness and species composition in young plantations, while in middle-aged and mature plantations it was mainly due to species replacement. The increase in prey abundance (and probably the increase in vegetation complexity and the decrease of extreme microclimatic conditions) through the plantation cycle increase the suitability for native forest species. However, a deeper understanding of the ecological and physiological requirements of spiders is necessary to improve the ability of tree plantations for native diversity.

Biotic filtering and mass effects in small shrub patches: is arthropod community structure predictable based on the quality of the vegetation?

1. Community assembly is affected by four processes: dispersal, filtering effects (selection), ecological drift and evolution. The role of filtering relative to dispersal and drift should decline with patch size, hampering possibilities to predict which organisms will be observed within small‐sized patches. However, vegetation structure is known to have a marked impact on species assemblages, and plant quality may act as a biotic filter. This challenges the assumption of unpredictable species assemblages in small‐sized vegetation patches.2. Using 32 stands of five shrub species in south‐west Finland, this study investigated whether biotic filtering effects caused by patch‐forming plants are strong enough to overcome the mixing of mobile arthropod assemblages across small patches.3. Stochastic variation did not hide the signals of biotic filtering and dispersal in the small shrub patches. Habitat richness around the patches explained a three times larger share of variation in the species composition than did the identity of the patch‐forming plant, but it had less effect on the abundance of arthropods. A radius of 50–100 m around a patch explained the species composition best.4. Abundance patterns varied between the feeding guilds; the patch‐forming shrub influenced the abundances of detritivores and leaf‐feeding herbivores, whereas the abundances of flower‐visiting herbivores appeared to track the flowering phenology of the plants. Shrub identity had little effect on omnivores or predators. Predator abundances were correlated with the abundance of potential prey.5. The results of this study suggest that community composition within a vegetation patch may be predictable even if dispersal overrides local filtering effects, as suggested by the mass‐effects paradigm.