This study utilized a 20-year dataset of seal counts from two neighboring harbours in the Solent region of south England. There is a need for monitoring of regional and local populations to understand overall trends. While grey seals are typically increasing in number, harbour seals have shown varying trends in recent decades following repeated pandemics. Harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus) both occur within the UK, but display regional contrasting population trends. Insights from the study of gradients of mammalian biodiversity should address the challenges of conservation in a rapidly changing world. Changes in global climate and land use are disrupting the integrity of biogeographic patterns. Accordingly, future work should integrate modern and historical patterns of taxonomic richness with phylogenetic and functional diversity of different clades and ecological subsets of continental faunas. Nonetheless, variation across different phylogenetic and ecological subsets of continental mammalian faunas illuminates the multifactorial, historical nature of biodiversity gradients in terms of the diversification history of clades, variation in resources that support species with different ecological traits, and changes in landscapes over time. Contemporary gradients are for the most part general. We review these gradients for mammalian assemblages of today and over geologic time. Principal among these patterns are the species–area relationship, as well as latitudinal, elevational, and topographic gradients. Mammalian biodiversity exhibits strong geographic gradients that correspond to variation in the physical environment (habitat, area, climate, and landforms) and reflect biogeographic processes that have unfolded over millennia. The heterogeneity and weakness of spatial data seriously constrain their utility to global and also sub-global scale conservation analyses. We review currently available databases for mammals globally and show that they are highly variable in complying with these attributes.
Distribution maps must satisfy additional attributes if used for conservation analyses and strategies, including minimizing commission and omission errors, credibility of the source/assessors and availability for public screening.
We recommend that before point location data are used to produce and/or evaluate distribution models, the dataset should be assessed under a set of criteria, including sample size, age of data, environmental/geographical coverage, independence, accuracy, time relevance and (often forgotten) representation of areas of permanent and natural presence of the species. We discuss the attributes that point location data and distribution maps must satisfy in order to be useful in conservation planning.
A variety of modelling approaches are used to transform point locations into maps. The first are often temporally and spatially biased, and too discontinuous, to be useful (untransformed) in spatial analyses. Spatial data on species distributions are available in two main forms, point locations and distribution maps (polygon ranges and grids).
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