Invasive species are one of the main threats to biodiversity worldwide and the processes enabling their establishment and persistence remain poorly understood. In generalist consumers, plasticity in ...diet and trophic niche may play a crucial role in invasion success. There is growing evidence that invasive ants, in particular, occupy lower trophic levels in their introduced range compared to the native one, but evidences remain fragmented. We conducted stable isotope analysis at five locations distributed on two continents to infer the trophic position of the invasive ant Formica paralugubris in the native and introduced part of the range. This species forms large colonies and can be a voracious predator while feeding on sugar‐based resources as well. Whereas native populations had trophic positions comparable to that of an omnivore, the introduced populations varied from being honeydew specialists to top predators, or omnivore. Where other ant species co‐occurred, there was no overlap in their trophic niches, and F. paralugubris occupied the lower position, suggesting that trophic displacement may enable the coexistence of different ant species. Taken together, our results suggest that shifts in diet associated with changes in the trophic niche of introduced species might mediate invasion success and enable long‐term coexistence with native species.
Sexual selection is an intense evolutionary force, which operates through competition for the access to breeding resources. There are many cases where male copulatory success is highly asymmetric, ...and few males are able to sire most females. Two main hypotheses were proposed to explain this asymmetry: "female choice" and "male dominance". The literature reports contrasting results. This variability may reflect actual differences among studied populations, but it may also be generated by methodological differences and statistical shortcomings in data analysis. A review of the statistical methods used so far in lek studies, shows a prevalence of Linear Models (LM) and Generalized Linear Models (GLM) which may be affected by problems in inferring cause-effect relationships; multi-collinearity among explanatory variables and erroneous handling of non-normal and non-continuous distributions of the response variable. In lek breeding, selective pressure is maximal, because large numbers of males and females congregate in small arenas. We used a dataset on lekking fallow deer (Dama dama), to contrast the methods and procedures employed so far, and we propose a novel approach based on Generalized Structural Equations Models (GSEMs). GSEMs combine the power and flexibility of both SEM and GLM in a unified modeling framework. We showed that LMs fail to identify several important predictors of male copulatory success and yields very imprecise parameter estimates. Minor variations in data transformation yield wide changes in results and the method appears unreliable. GLMs improved the analysis, but GSEMs provided better results, because the use of latent variables decreases the impact of measurement errors. Using GSEMs, we were able to test contrasting hypotheses and calculate both direct and indirect effects, and we reached a high precision of the estimates, which implies a high predictive ability. In synthesis, we recommend the use of GSEMs in studies on lekking behaviour, and we provide guidelines to implement these models.
The decomposition of beta-diversity (β-diversity) into its replacement (β
) and richness (β
) components in combination with a taxonomic and functional approach, may help to identify processes ...driving community composition along environmental gradients. We aimed to understand which abiotic and spatial variables influence ant β-diversity and identify which processes may drive ant β-diversity patterns in Mediterranean drylands by measuring the percentage of variation in ant taxonomic and functional β-diversity explained by local environmental, regional climatic and spatial variables. We found that taxonomic and functional replacement (β
) primarily drove patterns in overall β-diversity (β
). Variation partitioning analysis showed that respectively 16.8%, 12.9% and 21.6% of taxonomic β
, β
and β
variation were mainly explained by local environmental variables. Local environmental variables were also the main determinants of functional β-diversity, explaining 20.4%, 17.9% and 23.2% of β
, β
and β
variation, respectively. Findings suggest that niche-based processes drive changes in ant β-diversity, as local environmental variables may act as environmental filters on species and trait composition. While we found that local environmental variables were important predictors of ant β-diversity, further analysis should address the contribution of other mechanisms, e.g. competitive exclusion and resource partitioning, on ant β-diversity.
The use of camera traps to estimate population size when animals are not individually recognizable is gaining traction in the ecological literature, because of its applicability in population ...conservation and management.
We estimated population size of synthetic animals with four camera trap sampling-based statistical models that do not rely on individual recognition. Using a realistic model of animal movement to generate synthetic data, we compared the random encounter model, the random encounter and staying time model, the association model and the time-to-event-model and we investigated the impact of violation of assumptions on the population size estimates.
While under ideal conditions these models provide reliable population estimates, when synthetic animal movements were characterised by differences in speed (due to diverse behaviours such as locomotion, grazing and resting) none of the model provided both unbiased and precise density estimates. The random encounter model and the time-to-event-model provided precise results but tended to overestimate population size, while the random encounter and staying time model was less precise and tended to underestimate population size. Lastly, the association model was unable to provide precise results. We found that each tested model was very sensitive to the method used to estimate the range of the field-of-view of camera traps. Density estimates from both random encounter model and time-to-event-model were also very sensitive to biases in the estimate of animals’ speed. We provide guidelines on how to use these statistical models to get population size estimates that could be useful to wildlife managers and practitioners.
Random walks are common in nature and are at the basis of many different phenomena that span from neutrons and light scattering to the behaviour of animals. Despite the evident differences among all ...these phenomena, theory predicts that they all share a common fascinating feature known as Invariance Property (IP). In a nutshell, IP means that the mean length of the total path of a random walker inside a closed domain is fixed by the geometry and size of the medium. Such a property has been demonstrated to hold not only in optics, but recently also in the field of biology, by studying the movement of bacteria. However, the range of validity of such a universal property, strictly linked to the fulfilment of equilibrium conditions and to the statistical distributions of the steps of the random walkers, is not trivial and needs to be studied in different contexts, such as in the case of biological entities occupied in random foraging in an open environment. Hence, in this paper the IP in a virtual medium inside an open environment has been studied by using actual movements of animals recorded in nature. In particular, we analysed the behaviour of a grazer mollusc, the chiton Acanthopleura granulata. The results depart from those predicted by the IP when the dimension of the medium increases. Such findings are framed in both the condition of nonequilibrium of the walkers, which is typical of animals in nature, and the characteristics of actual animal movements.
Red wood ants are ecologically dominant species that affect the composition of the invertebrate community. In the past century, one of these species, Formica paralugubris (Seifert 1996), was ...introduced outside its native area (the Alps), in the Apennines (Italy). Here we investigated the effect of the presence of an introduced population of F. paralugubris on the frequency of nests of other ant species in Abetone, Central Apennines. Ant nests were found only in the area unoccupied by F. paralugubris. In this area, we also found one pleometrotic association between queens of Lasius flavus (Fabricius, 1782) and two plesiobiotic associations, one between Formica fusca (Linnaeus, 1758) and L. flavus and the other one between Myrmica ruginodis (Nylander, 1846) and L. flavus. This latter is the first plesiobiotic relationship reported between these two species, the second reported for M. ruginodis and the 10th for L. flavus. Additionally, this is the first plesiobiotic association reported for the Mediterranean region and Southern Europe.
Nest-mate recognition plays a key role in the biology of ants. Although individuals coming from a foreign nest are, in most cases, promptly rejected, the degree of aggressiveness towards non ...nest-mates may be highly variable among species and relies on genetic, chemical and environmental factors. We analyzed intraspecific relationships among neighboring colonies of the dominant Mediterranean acrobat ant Crematogaster scutellaris integrating genetic, chemical and behavioral analyses. Colony structure, parental relationships between nests, cuticular hydrocarbons profiles (CHCs) and aggressive behavior against non nest-mates were studied in 34 nests located in olive tree trunks. Bayesian clustering analysis of allelic variation at nine species-specific microsatellite DNA markers pooled nests into 14 distinct clusters, each representing a single colony, confirming a polydomous arrangement of nests in this species. A marked genetic separation among colonies was also detected, probably due to long distance dispersion of queens and males during nuptial flights. CHCs profiles varied significantly among colonies and between nests of the same colony. No relationship between CHCs profiles and genetic distances was detected. The level of aggressiveness between colonies was inversely related to chemical and spatial distance, suggesting a 'nasty neighbor' effect. Our findings also suggest that CHCs profiles in C. scutellaris may be linked to external environmental factors rather than genetic relationships.
A trophic niche overlap in native and alien turtle species can lead to competitive interactions whereby allochthonous turtles may outcompete autochthonous individuals and eventually affect viability ...of natural populations. The European pond turtle (
Emys orbicularis
) is an autochthonous species threatened by habitat encroachment and competition with the red-eared slider (
Trachemys scripta elegans
). The latter is an invasive species introduced in Europe from midwestern United States as a pet and now widespread in the natural habitats of
E. orbicularis
. The extent of trophic competition between
E. orbicularis
and
T. s. elegans
in northern Italy was assessed by nitrogen and carbon stable isotope analysis (δ
15
N and δ
13
C). We used blood and claw samples in order to obtain information on diet components over a short- (3–4 months) and long-term (12 months) time frame, respectively. Analysis of claw samples showed a clear separation between the diets of adults of the two species, but suggested a trophic overlap among adult invaders and young autochthonous turtles. Blood samples, on the other hand, revealed a partial overlap between niches, indicating a short-term correspondence in diet composition between species. We found that, for specific life stages and times of the year, there is potential for trophic competition, which may have important consequences for the management and conservation of
E. orbicularis
in Italy.
Efforts for the conservation of green turtles (
Chelonia mydas
) in the Chagar Hutang Turtle Sanctuary (CHTS), Redang Island, Malaysia, have been in place for over two decades. Here we propose that ...the recruitment of new mothers to this rookery has a significant influence on the recovery of nest abundance in the long term. A 2–3 years’ quasi-periodic oscillation in nest abundance was also observed. This fluctuation might have been a consequence of El Niño-Southern Oscillation (ENSO), which affects sea-surface temperature (SST) in the South China Sea (SCS) in the months following El Niño/La Niña events. To test these hypotheses, the number of clutches laid in the CHTS over a 24-year period was assessed via the Seasonal and Trend Decomposition by Loess (STL) algorithm. The long-term trend of nest abundance was shown to be dependent on the recruitment of new mothers, while a 2–3 years’ quasi-periodic oscillation in nest abundance showed a 2.5-year-lagged negative correlation to the Oceanic Niño Index (ONI) and a 2-year-lagged negative correlation to the SST data series from SCS shallow waters, including known foraging grounds of green turtles nesting in the CHTS. In summary, we demonstrated that La-Niña peaks by decreasing SST in the SCS for the subsequent semester promotes green turtle nesting after 2–3 years. These results highlight the influence of broad climatological fluctuations in the sea turtles’ life cycle and the importance of conservation measures to secure their entire home range and life stages.
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