Browsing by Author "Kueffer, Christoph"
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- Colonization and diversification shape species-area relationships in three Macaronesian archipelagosPublication . Price, Jonathan P.; Otto, Rüdiger; Sequeira, Miguel Menezes de; Kueffer, Christoph; Schaefer, Hanno; Caujapé-Castells, Juli; Fernández-Palacios, José MaríaAim: Species–area relationships (SARs) on oceanic archipelagos are shaped at least as much by speciation as by immigration–extinction dynamics. We examine three well‐studied Atlantic archipelagos to quantify the relative contributions of coloniza tion and diversification to individual and whole‐archipelago floras. Location: Three Macaronesian archipelagos: the Azores, Madeira and Canary Islands. Methods: We assessed the floras of all three archipelagos in order to compare SARs and numbers of endemic species with respect to the physical characteristics of each archipelago (geological age, isolation, and environmental diversity). Utilizing a large number of available phylogenies, we partitioned each flora into putative colonist lin eages. These were used to determine: (a) the number of original colonists of each archipelago, (b) degree of relatedness among these, and (c) the degree to which internal diversification contributes to species numbers for islands and archipelagos with different physical characteristics. Results: Archipelagos varied in the parameters of the SARs in relation to their phys ical characteristics. The Canarian and Madeiran floras demonstrate remarkably simi lar SARs with z values (slopes) near 0.3, while the Azorean flora exhibits fewer species per given area and a modest z value of 0.15. The Canarian and Madeiran endemic species are concentrated in a small number of diversifying lineages, whereas the Azorean endemics were mostly in anagenetic lineages (indicating mini mal internal diversification). Lineages that do not diversify within a given archipelago significantly tend not to diversify in others, whereas diversifying lineages tend to have more species in the Canarian flora when compared with related lineages in the others. Main conclusions: Although a strong independent effect of island area on species richness exists for the whole Macaronesian region, colonization and diversification are also influenced by geological age and environmental diversity of archipelagos, overriding characteristics of individual islands (“archipelago effect”). The “Azorean diversity enigma” likely results from a combination of geological youth, low environmental diversity and disproportionate human alteration.
- Topography-driven isolation, speciation and a global increase of endemism with elevationPublication . Steinbauer, Manuel J.; Field, Richard; Grytnes, John-Arvid; Trigas, Panayiotis; Ah-Peng, Claudine; Attorre, Fabio; Birks, H. John B.; Borges, Paulo A. V.; Cardoso, Pedro; Chou, Chang-Hung; De Sanctis, Michele; Sequeira, Miguel M. de; Duarte, Maria C.; Elias, Rui B.; Fernández-Palacios, José María; Gabriel, Rosalina; Gereau, Roy E.; Gillespie, Rosemary G.; Greimler, Josef; Harter, David E. V.; Huang, Tsurng-Juhn; Irl, Severin D. H.; Jeanmonod, Daniel; Jentsch, Anke; Jump, Alistair S.; Kueffer, Christoph; Nogué, Sandra; Otto, Rüdiger; Price, Jonathan; Romeiras, Maria M.; Strasberg, Dominique; Stuessy, Tod; Svenning, Jens-Christian; Vetaas, Ole R.; Beierkuhnlein, CarlAim Higher-elevation areas on islands and continental mountains tend to be separated by longer distances, predicting higher endemism at higher elevations; our study is the first to test the generality of the predicted pattern. We also compare it empirically with contrasting expectations from hypotheses invoking higher speciation with area, temperature and species richness. Location Thirty-two insular and 18 continental elevational gradients from around the world. Methods We compiled entire floras with elevation-specific occurrence information, and calculated the proportion of native species that are endemic (‘percent endemism’) in 100-m bands, for each of the 50 elevational gradients. Using generalized linear models, we tested the relationships between percent endemism and elevation, isolation, temperature, area and species richness. Results Percent endemism consistently increased monotonically with elevation, globally. This was independent of richness–elevation relationships, which had varying shapes but decreased with elevation at high elevations. The endemism–elevation relationships were consistent with isolation-related predictions, but inconsistent with hypotheses related to area, richness and temperature. Main conclusions Higher per-species speciation rates caused by increasing isolation with elevation are the most plausible and parsimonious explanation for the globally consistent pattern of higher endemism at higher elevations that we identify. We suggest that topography-driven isolation increases speciation rates in mountainous areas, across all elevations and increasingly towards the equator. If so, it represents a mechanism that may contribute to generating latitudinal diversity gradients in a way that is consistent with both present-day and palaeontological evidence.