Global distribution and conservation status of ecologically rare mammal and bird species

Abstract

Identifying species that are both geographically restricted and functionally distinct, i.e. supporting rare traits and functions, is of prime importance given their risk of extinction and their potential contribution to ecosystem functioning. We use global species distributions and functional traits for birds and mammals to identify the ecologically rare species, understand their characteristics, and identify hotspots. We find that ecologically rare species are disproportionately represented in IUCN threatened categories, insufficiently covered by protected areas, and for some of them sensitive to current and future threats. While they are more abundant overall in countries with a low human development index, some countries with high human development index are also hotspots of ecological rarity, suggesting transboundary responsibility for their conservation. Altogether, these results state that more conservation emphasis should be given to ecological rarity given future environmental conditions and the need to sustain multiple ecosystem processes in the long-term.

Fig. 1. Ecologically rare species are defined by the combination of geographical restrictiveness and functional distinctiveness.

a, b Relationship between functional and geographical restrictiveness of mammals and birds. Geographical restrictiveness is defined as the inverse of geographic distribution while functional distinctiveness measures how the traits of a species are original compared to all the other species. We use log(1- restrictiveness) for clarity as most of the restrictiveness values are close to 0 for mammals and birds). Each species is represented by a dot, ecologically rare species are in red, average in blue, and common in orange. Icons were generated using R (rphylopic package) and are under the Public Domain Dedication 1.0 license.

Fig. 2. Ecologically rare fill a wide breadth of ecological strategies in the Eltonian niche space.

Principal Coordinates Analysis (PCoA) representing the functional space of mammals (a) and birds (b) based on their functional traits. The two axes (PC2 and PC3 for mammals, PC2 and PC4 for birds,) explain respectively 35.3% and 26.4% of the variance in the distance matrix (see Supplementary Tables 1 and 2). Species are colored by their functional distinctiveness values. Functional space of ecologically rare species is in red, common, and average species are respectively in orange and blue. Icons were generated using R (rphylopic package) and are under a public the Public Domain Dedication 1.0 license.

Fig. 3. Closely related species were not necessarily more similar in their degree of ecological rarity than distantly related species but ecological rarity is over-represented in some orders: Primate and Chiropotera for mammals and Psittaciformes, Caprimulgiformes, and Apodiformes (Strisores) for birds.

a, b Phylogenies of terrestrial mammals and birds. Functional distinctiveness values are represented on terminal branches (color gradient). Ecologically rare species are highlighted by red dots, common by orange and average by blue. Distribution of the values of phylogenetic signal of ecological rarities (index D) computed on 100 trees are plotted in the center of the tree. Orders names are indicated on the outside arcs. The figure represents a single phylogeny from the 100 phylogenies generated (see “Methods”). Icons were generated using R (rphylopic package) and are under the Public Domain Dedication 1.0 license.

Fig. 4. Global distribution of mammal and bird species considering only unglaciated areas.

a–c Distribution of total species richness, number of ecologically rare and common mammals, and d-f distribution of total species richness, number of ecologically rare and common birds. Icons were generated using R (rphylopic package) and are under the Public Domain Dedication 1.0 license.

Fig. 5. Vulnerability to current and future threats of ecologically rare, average, and common mammal and bird species.

a, b Percentage of species per IUCN status according to criteria by the IUCN Red List, Threatened (TH red: Vulnerable, Endangered, Critically Endangered), Least concern (LC green: Least Concern and Near Threatened) and Not Evaluated (NE gray: Not Evaluated or inadequate information). c, d Human Footprint that measure the cumulative impact of direct human pressures; e, f Human development index (HDI) which is a statistic composite index of life expectancy, education, and per capita income indicators; g, h Change in distribution range based on climate change projections (scenario RCP 8.5, Horizon 2041–2060, see Supplementary Fig. 10 for Horizon 2061–2080) and i, j Target achievement (extent to which species are represented within PAs regarding their restrictiveness). Symbol indicate significant similar distribution between groups (P < 0.05, See Supplementary Table 3 for all p value) via one-way ANOVA and Tukey’s post-hoc tests. Icons were generated using R (rphylopic package) and are under the Public Domain Dedication 1.0 license.