Journal of Zoology最新文献

Species with sympatric distribution influence ecosystem dynamics and are impacted by the presence of other co-existing species. Understanding how environmental factors and interspecific interactions influence the co-occurrence of sympatric species is vital for comprehending the assembly of biological communities and the processes driving ecosystem regulation and development. This study investigated the co-occurrence patterns and interspecific interactions among three species—the Siberian weasel (Martes flavigula), yellow weasel (Mustela sibirica), and Temminck's tragopan (Tragopan temminckii) in the Wanglang National Nature Reserve, China. The study of the interspecific relationships among these three species is of great significance as it can provide in-depth insights into the complex ecological mechanisms within the ecosystem. It helps us better understand how these species interact with each other, which in turn affects the overall stability and functionality of the ecosystem. Utilizing monitoring data from 50 camera traps deployed between 2011 and 2015, combined with quadrat surveys, a multi-species occupancy model was applied to assess the influence of various environmental factors on their occupancy. The results indicated that M. flavigula exhibited the lowest marginal occupancy probability (Ψ = 0.35, 95% CI: 0.18–0.55), followed by M. sibirica (Ψ = 0.35, 95% CI: 0.18–0.54), while T. temminckii displayed the highest value (Ψ = 0.42, 95% CI: 0.27–0.59). The top model revealed that the co-occurrence probability of M. flavigula with M. sibirica and with T. temminckii both increases as forest canopy density rises. Additionally, the co-occurrence probability between M. flavigula and T. temminckii remained consistently high, likely influenced by other wildlife interactions and anthropogenic factors. These findings enhance our understanding of the co-occurrence patterns of these species and provide valuable insights for future research on species interactions and long-term ecosystem sustainability.

We investigated the feeding habits and dietary patterns of Yacare (Caiman yacare) in freshwater wetlands located in the province of Corrientes, Argentina, with a focus on how these habits relate to the size of the caiman. A total of 39 caimans were classified into different groups based on their total length, including hatchlings (Class I), juveniles (Class II), and adults (Class III and IV). Stomach contents were obtained through gastric lavage. Insects (Coleoptera, Orthoptera, Odonata, and Hemiptera), mollusks (Pomacea sp.), and freshwater crustaceans (Pseudopalaemon sp. and Trichodactylus sp.) were the most common prey, while reptiles, fish, and birds were less frequently consumed. Remains of aquatic plants such as Pistia sp., Azolla sp., and Elodea sp. were also found. Prey diversity and diet composition were similar across the size classes of caimans. As the size of C. yacare increased, smaller prey were not excluded in order to consume larger prey. Larger caimans had larger Pomacea sp. opercula in their stomachs, potentially linked to morphological constraints, such as the limitation in jaw opening. Our findings suggest that Caiman yacare incorporates a variety of prey into its feeding behavior, and there is no abrupt change in dietary pattern as the caimans grow in size.

The theory of sex allocation in simultaneous hermaphrodites predicts that resource investment between male and female reproductive functions varies with the size of the mating group. To test this theory in commensal flatworms that are simultaneous hermaphrodites, in the present study, we evaluated the variations in the sizes of male and female gonads in Temnocephala iheringi (Platyhelminthes, Rhabdocoela), a species that inhabits the pallial cavity of the golden apple snail Pomacea canaliculata (Mollusca: Gastropoda). We evaluated two snail populations, each naturally exhibiting different infestation intensities of T. iheringi, assuming distinct mating group sizes. We found that the total size of the gonads of flatworms from both snail populations was similar, but that the proportion of the male gonad was higher in flatworms from the snail population with higher infestation intensity (larger mating group) than in those from the snail population with lower infestation intensity. Additionally, the proportion of the female gonad was lower in flatworms from the snail population with higher infestation intensity. These findings support the theory of sex allocation and, for the first time, demonstrate differences in gonadal sex allocation in a commensal organism in its natural environment.

For predators that feed on a restricted set of prey resources, individuals must be able to withstand shortages of their required prey. Additionally, when morphological traits make prey access body size-dependent, changes in prey availability might disproportionately alter access to those resources for different cohorts within a population. In a 3-year laboratory study, we housed and fed a colony of African egg-eating snakes (Dasypeltis scabra), an obligate bird egg specialist, to quantify their ingestion ability and annual feeding requirements. Using those data, we estimated monthly trends of the accessibility and availability of bird eggs suitable for consumption by differently sized individuals. We estimate that adult and neonate D. scabra can ingest the eggs of 708 of 728 bird species (98%) and 363 of 728 bird species (50%), respectively. Eggs are widely available during warm spring and summer months, but bird breeding declines during colder winter months, especially for species laying smaller eggs. In the laboratory, snakes showed a seasonal feeding rhythm with high food acceptance coinciding with peaks in monthly bird egg-laying during the austral spring and summer. Our snakes required food equal to only 61% of initial body mass annually to maintain body condition and consumed on average just 2.4 times more food than maintenance levels, corroborating metabolic studies showing low metabolic rates in Dasypeltis. Our findings suggest that seasonal fluctuations of prey availability are likely the selective pressure that contributed to increased ingestion ability (so that smaller snakes could potentially access larger eggs that are more readily available through cooler months) and reduced metabolic rates in D. scabra, which shaped their low feeding requirements. Thus, while seasonal variation in prey availability does not preclude bird egg specialization within D. scabra, it directly influences when these snakes feed as well as how many eggs they consume annually.

Understanding species' movements and behavioural ecology after the breeding season is crucial to improving conservation efforts. This study investigates the post-breeding movements of Hen Harriers (Circus cyaneus) using GPS/GSM data from 30 individuals over 54 periods from 2019 to 2023. Using maximum and mean distances from the reproductive centroid as a behavioural proxy, we classified post-breeding movements into three strategies: migration (22.2%), sedentarism (9.3%), and sedentarism with post-breeding movements (68.5%). Our results challenge the previous assumptions that most of the Spanish Hen Harrier population was sedentary. The study shows a relationship between distance travelled and latitude of breeding areas, suggesting environmental adaptation. The Spanish Hen Harrier population, being at the southern limit of its breeding range, exhibits less pronounced differences between sexes or strategies. Raptors that migrate extensively may be more vulnerable due to a reduction of the area available for post-breeding movements.

Bulk stable isotope analysis of carbon and nitrogen is commonly used to assess trophic relationships. However, compound-specific stable isotope analysis of individual amino acids may be a more accurate approach for resolving food web structure. Nevertheless, recent studies suggest amino acid-specific nitrogen trophic discrimination factors (TDFs) can vary depending on the type of nitrogenous waste produced and the quality of the diet, potentially limiting inference. We compared the ability to discriminate between primary and secondary consumers using bulk and compound-specific methods in an Arctic tundra ecosystem. Specifically, we determined bulk δ¹³C and δ¹⁵N values, as well as amino acid-specific δ¹⁵N values, for red blood cells from nestling golden eagles (Aquila chrysaetos), rough-legged hawks (Buteo lagopus), and gyrfalcons (Falco rusticolus), as well as for muscle samples from common prey species. We subsequently used high-precision diet estimates from nest cameras to estimate TDFs for gyrfalcon nestlings and compare these against TDFs for other taxa from the literature. Although bulk δ¹⁵N values of secondary consumers were enriched relative to primary consumers, overlap occurred across groups, and greater separation was apparent using δ¹⁵N of amino acids. Comparing red blood cell δ¹⁵N values to prey muscle δ¹⁵N values, bulk TDFs and compound-specific TDFs for trophic amino acids were lower than values from the literature that have typically been used to estimate trophic position. Amino acid-specific TDFs for raptor nestlings may be particularly low due to their rapid growth, consumption of high-quality protein, and excretion of nitrogenous wastes as uric acid, which have previously been identified as factors influencing isotopic discrimination. Consistent with recent studies, our findings indicate that the use of ‘universal’ TDF_Glu-Phe values will result in an underestimate of nestling trophic level, and more work is needed to establish appropriate TDFs that reflect the physiology and life-history stage of the consumer.

Geographic size variation in ectotherms often reflects complex interactions between environmental and evolutionary factors, which can differ among taxa. In this study, we investigated body size patterns in two sister subspecies of spur-thighed tortoises, Testudo graeca whitei and T. g. marokkensis, across their natural ranges in North Africa. These subspecies show distinct climatic niches, and we hypothesized that their morphology would differ in response to environmental variables, such as climate, Normalized Difference Vegetation Index (NDVI, a measure of vegetation cover), latitude, and elevation. We measured tortoises across Morocco and Algeria to explore growth patterns and adult body size in response to these environmental factors. Growth models revealed significant sexual size dimorphism in both subspecies. The humid subspecies T. g. marokkensis exhibited a slower growth rate but reached a larger asymptotic size compared with the semiarid T. g. whitei. When evaluating the relationship between body size and environmental factors, we found that T. g. whitei exhibited a negative correlation between body size and latitude, which contrasts with Bergmann's rule. By contrast, T. g. marokkensis followed the rule, with body size positively correlated with both latitude and elevation. Our findings suggest that latitude and elevation are encompassing critical factors influencing body size, reflecting the impact of climatic factors like aridity on tortoise morphology. We also found that body size patterns aligned with niche divergence, with larger individuals of both sexes occurring in regions with more favorable climatic conditions. Indirectly, these results suggest that larger body size in T. graeca may be associated with higher fitness in both males and females.

Endocrine regulation and hormonal responses determine the capacity of an organism to cope with changing environmental conditions, such as variable or extreme temperatures. Hormones can also be regarded as “sensors” for environmental signals and as indicators of an organism's or populations' fitness. The levels of glucocorticoid hormones, such as corticosterone, are generally used as biomarkers for physiological stress and metabolic rate variations, while thyroid hormones (i.e., triiodothyronine—T3) are regarded as indicators of nutritional and thermal stress in birds. The Pyrenean Capercaillie (Tetrao urogallus aquitanicus) is an endangered galliform adapted to cold weather, and its population is in steep decline. This study used a noninvasive approach to assess hormone levels in the Pyrenean Capercaillie, in a first attempt to understand how hormone levels may respond to certain environmental variables. We determined the corticosterone and T3 levels in 139 freshly molted covert feathers of 113 Pyrenean Capercaillies (80 from Spain and 33 from France) using enzyme immunoassays. The relationships between hormone levels and several biotic and abiotic variables were assessed. Our findings showed that corticosterone levels were lower in feathers found further away from areas of human leisure activity (i.e., cycling trails). Lower corticosterone levels were also found in certain biogeographical areas (i.e., Northern Pyrenees and Pre-Pyrenees), suggesting that corticosterone levels may respond to certain climate-related variables (such as precipitation or temperature). Conversely, T3 levels were influenced by sex and feather length, but did not correlate with any of the environmental variables. The lack of statistically significant differences in corticosterone and T3 in relation to the types of covert feathers analyzed facilitates the collection process for noninvasive studies. Additional hormonal studies could provide essential data to understand the level of endocrine flexibility of the Pyrenean Capercaillie in response to external variables, which may ultimately define the species' resilience to climate change and other drivers of environmental variation.

Odontocetes are key predators in marine food webs, but knowledge of their habitat use and trophic niche still needs to be improved. In this study, we used carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotopes to identify the trophic position, isotopic niche size, foraging habitat, and potential sex-based differences in the dietary patterns of six odontocete species in the Madeira Archipelago: short-beaked common dolphin (Delphinus delphis), Atlantic spotted dolphin (Stenella frontalis), common bottlenose dolphin (Tursiops truncatus), false killer whale (Pseudorca crassidens), short-finned pilot whale (Globicephala macrorhynchus), and sperm whale (Physeter macrocephalus). Results delineated two distinct groups. The first (common dolphin, spotted dolphin, bottlenose dolphin) exhibited lower δ¹³C and δ¹⁵N values, lower trophic positions, and larger isotopic niches, indicating that these species are generalist predators and rely more on the pelagic food web. The second group (false killer whale, short-finned pilot whale, sperm whale) displayed higher isotopic values and trophic positions, with smaller isotopic niches, relying more on shallow-to-deep mix food webs and displaying a more specialist diet. This distinction was further supported by comparisons with stable isotope values of potential prey species. However, for deep-diving species such as short-finned pilot whale and sperm whale, some prey species were not represented in the niche models due to lack of available samples. The isotopic niche overlap was highest for two pairs of species: spotted and bottlenose dolphin, probably related to their generalist diet and temporal co-occurrence; false killer whale and short-finned pilot whale, from which no interspecific competition is expected due to differing habitat preferences. No sex-related differences were found in the five species analyzed for either isotope. This study characterizes the trophic ecology of several oceanic odontocetes in the Eastern North Atlantic and establishes a valuable baseline for future research. Understanding the trophic interactions of these species offers important insights into their ecological roles and the dynamics of the marine ecosystem they inhabit.

In many bird species, such as the common chiffchaff Phylloscopus collybita, the geographic variation in song is a crucial factor in determining intraspecies diversity. However, capturing this variation in trans-Palearctic species can be challenging due to their wide ranges. We present an almost continent-wide study spanning from Germany to Yakutia, covering Western European, Eastern European, and Siberian chiffchaff subspecies, and including a broad zone of hybridization between the latter. The novel fine-scale differentiation patterns are revealed through a detailed analysis of local repertoire variability, including the diversity and geographic distribution of syllables, coupled with quantitative measures of rhythmic structure, frequency, and temporal song characteristics. Our study shows pronounced geographic variation across the entire chiffchaff range, with a distinct eastward trend characterized by an increase in singing speed and vocal repertoire size, a decrease in both the maximum and minimum frequencies, and a higher proportion of syllables with ascending modulation.