How do intrinsic and extrinsic causes interact in the extinction vulnerability of South American savanna shrub and tree species?

Although a growing body of literature recognises the importance of rarity for biodiversity conservation, it is unclear how the interaction of different forms of rarity, extrinsic causes of extinction, and protection affect species' vulnerability. Here we addressed the extinction vulnerability of 2203 shrub and tree species of the South American savanna (SAS). For this, species were attributed a form of rarity, a synergistic risk index (SRI), and a protection index (PI). The SRI combines three extrinsic causes of extinction (climate hazard, fire frequency, and human footprint). The PI is the ratio between the number of a species occurrences within protected areas and the total number of occurrences in the SAS. By combining the SRI and PI, we classified common and rare species into five vulnerability classes. Some regions of the SAS show high values of climate hazard, fire frequency, human footprint, and SRI. Each extrinsic cause of extinction is differently distributed across the SAS and shows no or low spatial congruence with the SRI. Many species show a low ratio of occurrences within PAs, which in combination with high SRI results in high vulnerability to extinction. Surprisingly, the number of common species in the higher vulnerability classes is higher than of rare species. Common and rare species in different vulnerability classes occur in somewhat different locations across the SAS and mainly constitute spatially incongruent centres with high species richness. Given our results, we propose that strategies for the effective conservation of SAS species are challenging and must be carefully designed.

Dispersal spectrum of four forest types along an altitudinal range of the Brazilian Atlantic Rainforest / Espectro de dispersão de quatro formações florestais ao longo de um gradiente altitudinal da Mata Atlântica brasileira

In ecological communities, the proportion of plant species with different dispersal syndromes is known as the dispersal spectrum, which can result from different selective pressures such as climate. This is because variations in temperature, humidity, atmospheric pressure and precipitation result in distinct flora and fauna among different sites. If climate conditions along an altitudinal range act as a strong direct or indirect selective pressure on dispersal syndromes, the dispersal spectrum among plant communities in different altitudes should be distinct. We organized the dispersal syndromes in five hierarchical levels according to the levels of detail in diaspore morphology and, consequently, different degrees of specificity to the dispersers. Then we identified, within each hierarchical level, the syndromes of tree species of four forest types of the Atlantic Rainforest along a 1200 m altitudinal range in Southeast Brazil. Among 327 species, we found two syndromes in the most general hierarchical level (abiotic and biotic dispersal), three in the following level (wind, self and animal), three in the intermediate level (barochory, autochory and endozoochory), two in the forth level (mammal and bird), and 12 syndromes in the most specific level, all of which were related to the morphology of diaspores dispersed by wind, autochory, mammals and birds. The dispersal spectrum in the five hierarchical levels was similar among the four forest types. Overall, the majority of species is dispersed by biotic agents, considered here as animals and the parent plant itself. Within biotic agents, the most important are animals, specifically birds. Most bird-dispersed species present drupoid diaspores. Our results indicate that the selective pressures on dispersal syndromes originated from climate conditions that vary with altitude are not strong, hence resulting in the same dispersal spectrum among the forest types.

Dentro de uma comunidade, a proporção de espécies vegetais com diferentes síndromes de dispersão é chamada de espectro de dispersão, o qual pode resultar de distintas pressões seletivas, como o clima. Isso ocorre porque variações na temperatura, umidade, pressão atmosférica e precipitação resultam em flora e fauna distintas entre locais. Assim, podemos esperar que o espectro de dispersão de comunidades vegetais em diferentes altitudes seja distinto se as condições climáticas ao longo do gradiente altitudinal atuarem como pressão seletiva direta ou indireta sobre as síndromes. Nós hierarquizamos as síndromes de dispersão em cinco níveis, de acordo com o detalhamento da morfologia dos diásporos e, consequentemente, seus diferentes graus de especificidade com os dispersores. Identificamos, em cada um dos níveis hierárquicos, as síndromes de espécies arbóreas de quatro formações florestais da Mata Atlântica ao longo de um gradiente altitudinal de 1200 m no sudeste do Brasil. Entre 327 espécies, encontramos duas síndromes no nível hierárquico mais geral (dispersão abiótica e biótica), três no nível seguinte (vento, própria planta parental e animais), três no nível intermediário (barocoria, autocoria e endozoocoria), duas no quarto nível (mamíferos e aves) e 12 síndromes no nível mais específico, relacionadas è morfologia dos diásporos dispersos pelo vento, autocoria, mamíferos e aves. O espectro de dispersão nos cinco níveis foi similar nas quatro formações florestais. De forma geral, a maior parte das espécies é dispersa por agentes bióticos, aqui considerados animais e a própria planta parental. Dentre os agentes bióticos, os mais importantes são os animais, especificamente as aves. A maioria das espécies dispersas pelas aves apresenta diásporos drupóides. Nossos resultados indicam que as pressões seletivas sobre as síndromes de dispersão ocasionadas pelas condições climáticas que variam com a altitude não são fortes. Assim, a ausência destas pressões seletivas resulta em um espectro de dispersão similar entre as formações florestais em diferentes altitudes.