Exploring the impact of temporal resolution on detecting shifts in the invasive species niche: Insights from Lessepsian fishes.

In this study, we estimate the niche overlap between native and invaded ranges of 36 Lessepsian fish, focusing on how this estimate might vary in relation to the temporal resolution of sea surface temperature and salinity, which are the main niche axes determining their distribution. Specifically, we wanted to address the following questions: (i) Does the choice of temporal averaging method of variables influence the estimation of niche overlap for individual variables? (ii) Does this temporal resolution effect persist when conducting bivariate niche estimations? Niches overlap was estimated by calculating two indices and these analyses were repeated at two temporal resolutions, matching observations to the classic 'multidecadal' average of environmental conditions and to the corresponding annual average of records. Results are compared with verify whether differences can be detected in the magnitude of niche commonality measured at annual or multidecadal temporal resolution. The findings show that the temporal resolution of the data significantly influences estimates of overlap in the thermal niche. Specifically, our analysis indicates a considerable disparity between native and invasive niche regions for most species, particularly when evaluated over multidecadal periods compared with matching occurrence data to the annual mean values of years the occurrence was observed, that is matching occurrence data to a common average of 'present' conditions or to the annual mean values of years of observation. In particular, the largest overlaps between native and invaded niches occur along the salinity axis, regardless of temporal resolution. When considering both temperature and salinity together, the results remain unaffected by the temporal resolution of the environmental data. Almost 30% of the species show a different niche in their introduced range, and for the other species, the overlap between native and invaded ranges was reduced with respect to the univariate analyses.

Spatio-temporal dynamics of exotic fish species in the Mediterranean Sea: Over a century of invasion reconstructed.

With over a thousand of introduced species, the Mediterranean is the most heavily invaded marine region in the world. Yet, the spatio-temporal dynamics of this bioinvasion has never been analysed. Examination of a comprehensive dataset of 4015 georeferenced observations, extracted from the scientific literature, allowed (i) reconstructing the invasion and the introduction and post-introduction dynamics of exotic fish species, (ii) calculating introduction and spread rates, and (iii) investigating the time correlates since introduction. Our analysis encompasses 188 fish species that entered the Mediterranean from 1896 to 2020, including 25 Atlantic species that naturally expanded their range through the Strait of Gibraltar. Cumulative occurrences, reported in 264 distribution maps, documented the progressive expansion of the most represented species and the spatio-temporal patterns associated with three introduction routes: the Suez Canal (CAN); other human-mediated vectors (HM) and the Strait of Gibraltar (NRE). The arrival rate of the species introduced through all three routes increased steeply after 1990, without a sign of saturation. Data analysis highlighted some temporal and geographical patterns, such as the effect and eventual weakening of the biogeographical barriers represented by the Strait of Sicily and the North Aegean Sea and the asymmetrical distribution of occurrences along the northern and southern Mediterranean coasts. Finally, there was an exponential increase in the secondary spread rates of CAN and NRE immigrants, as the more recent introductions achieved the fastest geographical expansions. Our findings provide a detailed and spatially explicit summary of a massive invasion that has changed the history of the Mediterranean biota and represent a remarkable example of rapid biotic homogenization in the global ocean.

ORMEF: a Mediterranean database of exotic fish records.

The Mediterranean Sea is recognized today as the World's most invaded marine region, but observations of species occurrences remain scattered in the scientific literature and scarcely accessible. Here we introduce the ORMEF database: a first comprehensive and robust compilation of exotic fish observations recorded over more than a century in the Mediterranean. ORMEF consists today of 4015 geo-referenced occurrences from 20 Mediterranean Countries, extracted from 670 scientific published papers. We collated information on 188 fish taxa that are thus divided: 106 species entered through the Suez Canal; 25 species introduced by shipping, mariculture, aquarium release or by means of other human activities; 57 Atlantic species, whose arrival in the Mediterranean has been attributed to the unassisted immigration through the strait of Gibraltar. Each observation included in the ORMEF database was submitted to a severe quality control and checked for geographical and taxonomic biases. ORMEF is a new authoritative reference for Mediterranean bio-invasion research and a living archive to inform management strategies and policymakers in a period of rapid environmental transformation.

Spatial predictions at the community level: from current approaches to future frameworks.

A fundamental goal of ecological research is to understand and model how processes generate patterns so that if conditions change, changes in the patterns can be predicted. Different approaches have been proposed for modelling species assemblage, but their use to predict spatial patterns of species richness and other community attributes over a range of spatial and temporal scales remains challenging. Different methods emphasize different processes of structuring communities and different goals. In this review, we focus on models that were developed for generating spatially explicit predictions of communities, with a particular focus on species richness, composition, relative abundance and related attributes. We first briefly describe the concepts and theories that span the different drivers of species assembly. A combination of abiotic processes and biotic mechanisms are thought to influence the community assembly process. In this review, we describe four categories of drivers: (i) historical and evolutionary, (ii) environmental, (iii) biotic, and (iv) stochastic. We discuss the different modelling approaches proposed or applied at the community level and examine them from different standpoints, i.e. the theoretical bases, the drivers included, the source data, and the expected outputs, with special emphasis on conservation needs under climate change. We also highlight the most promising novelties, possible shortcomings, and potential extensions of existing methods. Finally, we present new approaches to model and predict species assemblages by reviewing promising 'integrative frameworks' and views that seek to incorporate all drivers of community assembly into a unique modelling workflow. We discuss the strengths and weaknesses of these new solutions and how they may hasten progress in community-level modelling.

From continental priorities to local conservation: a multi-level analysis for African tortoises.

Terrestrial tortoises are the most endangered group of vertebrates but they are still largely ignored for defining global conservation priorities. In this paper, we explored within a hierarchical framework the potential contribution of prioritization studies at the continental scale to the planning of local initiatives for the conservation of African tortoises at the regional level. First, we modeled the distribution of all the African tortoise species, we calculated three indicators of conservation priority (i.e., species richness, conservation value, and complementarity), and we carried out a gap analysis at continental scale. Second, we focused on the most important region for tortoise conservation and performed the same analyses at higher resolution. Finally, we compared the results from the two scales for understanding the degree to which they are complementary. Southern Africa emerged from the continental analysis as the most important region for tortoises. Within this area, the high-resolution analysis pointed out specific core sites for conservation. The relative degree of species protection was assessed similarly at the two different resolutions. Two species appeared particularly vulnerable at both scales. Priority indices calculated at high resolution were correlated to the values calculated for the corresponding cells at low resolution but the congruence was stronger for species richness. Our results suggest to integrate the calculation of conservation value and complementarity into a hierarchical framework driven by species richness. The advantages of large scale planning include its broad perspective on complementarity and the capability to identify regions with greatest conservation potential. In this light, continental analyses allow targeting fine scale studies toward regions with maximum priority. The regional analyses at fine scale allow planning conservation measure at a resolution similar to that required for the practical implementation, reducing the uncertainty associated with low resolution studies.