Sperm whale population units, resident off inhabited islands, are an important source of ecosystem services for local communities and may be subject to greater anthropogenic pressures than their oceanic conspecifics.
The objectives of this review were to identify sperm whale-island specialists' habitats around the world and to assess the level of anthropogenic pressure on such nearshore populations. The hypothesis was that sperm whales with this ecological specialisation are rare and that the negative impacts they experience living close to inhabited shores may be also exacerbated by Anthropogenic Allee effect.
This study was conducted using a systematic literature review, following the principles recommended by the PRISMA guidelines, with a scoping of records of the presence of sperm whale social units in the territorial waters of countries around the world published between 2003 and 2023.
A review of 422 relevant research papers revealed only two places in the world where sperm whales with an island ecological specialisation exist, and there are negative trends in both. Such population units experience cumulative anthropogenic pressures 1.7–1.8 times higher than oceanic ones. The charisma and media popularity of sperm whales, combined with the rarity of observation sites for this species, may increase pressure, potentially accelerating their extinction (Anthropogenic Allee Effect). The results of the study are presented in the form of a narrative synthesis, tables and a map.
Determining the ecological specialisation of sperm whale population units should be a key component of management at both the local and species level. Exploitation of ecosystem services provided by island specialists should be strictly regulated in favour of sustainability, in order to preserve this rare ecological type.
The study of island species richness has gone far beyond traditional theories, as more and more studies attempt to include new predictor variables besides island area. Despite the rich bat diversity of Mediterranean islands, no studies have examined the factors influencing chiropteran species richness in such a geographic context.
We used Greek islands as a model to detect drivers of bat species richness based on a broad species occurrence dataset from islands of the Aegean and Ionian Seas, which was explored using 10 potential predictor variables.
Initially, we comprehensively evaluated all available data and sources for 53 Greek islands, deemed essential. This resulted in a reduced set of 28 islands. Predictors were grouped into three categories: island area, landscape diversity and island isolation. Generalised linear models were employed to identify the most significant factors explaining bat species richness in the 28 islands.
Tree cover and the distance between the islands and their nearest coast (mainland or island) best performed to predict bat species richness on Greek islands.
We show the important role of landscape composition and degree of isolation in influencing the distribution of bat species on islands.
We highlight the importance of forest habitats and the vital role of their management and protection, especially in the insular systems of the Mediterranean basin, where the risk of forest degradation or loss due to wildfires and land use change is especially high.
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