Differences in species–area relationships among the major lineages of land plants: a macroecological perspective

Abstract

Aim Although the increase in species richness with increasing area is considered one of the few laws in ecology, the role of environmental and taxon‐specific features in shaping species–area relationships (SARs) remains controversial. Using 421 land‐plant floras covering continents, continental islands and oceanic islands, we investigate whether variations in SAR parameters can be interpreted in terms of differences among lineages in speciation mode and dispersal capacities (TAXON), or of geological history and geographical isolation between continents and islands (GEO). Location Global. Methods Linear mixed‐effects models describing variation in SARs, depending on the factors GEO and TAXON and controlling for differences between realms (REALM) and biomes (BIOME). Results The best random‐effect structure included both random slopes and random intercepts for GEO, TAXON, REALM and BIOME. This accounted for 77% of the total variation in species richness, substantially more than the 27% statistically explained by the model with fixed effects only (i.e. the simple SAR). The slopes of the SARs were higher for oceanic islands than for continental islands and continents, and higher in spermatophytes than in pteridophytes and bryophytes. The intercepts largely exhibited the reverse trend. TAXON was included in best‐fit models restricted to oceanic and continental islands, but not continents. Analysing each plant lineage separately, the intercept of GEO was only included in the random structure of spermatophytes. Main conclusions SAR parameters varied considerably depending on geological history and taxon‐specific traits. Such differences in SARs among land plants challenge the neutral theory that the accumulation of species richness on islands is controlled exclusively by extrinsic factors. Taxon‐specific differences in SARs were, however, confounded by interactions with geological history and geographical isolation. This highlights the importance of applying integrative frameworks that take both environmental context and taxonomic idiosyncrasies into account in SAR analyses.

Bryophyte richness of soil islands on rocky outcrops is not driven by island size or habitat heterogeneity

“…Despite soil islands being one of the richest microhabitats of rocky outcrops of xeric environments (Silva et al 2014), the richness of bryophytes is naturally low in these habitats (Silva & Germano 2013;Silva et al 2014), probably because of the low tolerance of bryophytes to water deficit. This low level of species richness could decrease the predictive power of SAR (Patiño et al 2014), but this was not corroborated by other studies (e.g. Diamond & May 1977;Maly & Doolittle 1977;Abbott & Black 1980).…”

“…In a recent study, Patiño et al (2014) showed that SAR depends not only on neutral factors, but also on characteristics intrinsic to the organism, such as dispersion capacity, which involves specialized sexual diaspore production and frequency of sexual reproduction. Despite finding no SAR and no relationship between richness and environmental heterogeneity in the studied area, it is probable that intrinsic characteristics of bryophytes blur the effect of environmental factors on richness.…”

Diversity regulation at macro‐scales: species richness on oceanic archipelagos

“…Clearly, the results of our model are limited by the selection of the predictor variables and the sample size (although minimized by the use of LMMs, cf. Cabral et al ., ; Patiño et al ., ). The results could also be further supported, or challenged, by additional data that were not available in this study, such as the phylogenetic structure of communities, which provide information on the effect of area and other variables on the persistence times of island populations and rates of lineage splitting (e.g.…”

Determinants of orchid species diversity in world islands

“…Altitude and island geology have shown relatively weak albeit significant effects. Yet drivers of regional diversity may depart from these global patterns, and may also be taxon specific (Patiño et al ., ). Here we examine regional and global patterns of orchid diversity among island groups.…”