The flickering connectivity system of the north Andean páramos

Abstract

AND KEYWORDSAimTo quantify the effect of Pleistocene climate fluctuations on habitat connectivity across páramos in the Neotropics.LocationThe Northern AndesMethodsThe unique páramos habitat underwent dynamic shifts in elevation in response to changing climate conditions during the Pleistocene. The lower boundary of the páramos is defined by the upper forest line, which is known to be highly responsive to temperature. Here we reconstruct the extent and connectivity of páramos over the last 1 million years (Myr) by reconstructing the UFL from the long fossil pollen record of Funza09, Colombia, and applying it to spatial mapping on modern topographies across the Northern Andes for 752 time slices. Data provide an estimate of how often and for how long different elevations were occupied by páramos and estimates their connectivity to provide insights into the role of topography in biogeographic patterns of páramos.ResultsOur findings show that connectivity amongst páramos of the Northern Andes was highly dynamic, both within and across mountain ranges. Connectivity amongst páramos peaked during extreme glacial periods but intermediate cool stadials and mild interstadials dominated the climate system. These variable degrees of connectivity through time result in what we term the ‘flickering connectivity system’. We provide a visualization (video) to showcase this phenomenon. Patterns of connectivity in the Northern Andes contradict patterns observed in other mountain ranges of differing topographies.Main conclusionsPleistocene climate change was the driver of significant elevational and spatial shifts in páramos causing dynamic changes in habitat connectivity across and within all mountain ranges. Some generalities emerge, including the fact that connectivity was greatest during the most ephemeral of times. However, the timing, duration and degree of connectivity varied substantially among mountain ranges depending on their topographic configuration. The flickering connectivity system of the páramos uncovers the dynamic settings in which evolutionary radiations shaped the most diverse alpine biome on Earth.

Why mountains matter for biodiversity

“…The role of mountainous islands as refugia during periods of climate change has been shown for the conifers in New Caledonia, which originally derived from the Australian mainland (Condamine et al, 2017). Likewise, during ice ages local populations may persist on nunataks (exposed peaks otherwise surrounded by a glacier or snow), recolonizing downhill when the surrounding environment subsequently warms (Flantua & Hooghiemstra, 2018;Flantua et al, 2014;Flantua et al, 2019;Parducci et al, 2012).…”

Latitudinal patterns of species richness and range size of ferns along elevational gradients at the transition from tropics to subtropics

“…One explanation is that rugged mountainous terrain habitats with patchy distributions (‘sky islands’) support fragmented species populations that are more prone to speciation than species inhabiting extensive habitats without geographical barriers (Antonelli, Nylander, Persson, & Sanmartín, 2009; Kessler, 2001; Kruckeberg & Rabinovitz, 1985; McCormack, Huang, Knowles, Gillespie, & Clague, 2009). Besides, past climatic fluctuations determining the connectivity between sky islands may be an important driver of diversification by leading to successive cycles of population expansion and fragmentation (‘flickering connectivity systems’; Flantua & Hooghiemstra, 2018; Flantua, O'dea, Onstein, Giraldo, & Hooghiemstra, 2019). Clearly, understanding the spatial variation of species range sizes along latitudinal or elevational gradients requires more detailed understanding than suggested by the conceptually simply RR.…”

Synthesis of geological and comparative phylogeographic data point to climate, not mountain uplift, as driver of divergence across the Eastern Andean Cordillera

“…5) provides a clue that the interaction between life history and environment may play an important role in structuring variation across the Andes, as has been found in a related comparative phylogeographic study of frogs in Panama (Paz et al 2015). While the EC-MA was largely formed in the Late Eocene (38–33 Ma), climatic fluctuations continued and were especially strong during the Pleistocene (Flantua et al, 2019). The cooling in the Pliocene and subsequent Pleistocene climate oscillations likely created a ‘flickering connectivity’ (Flantua et al, 2019) between lowland populations east and west of the EC-MA, and the connectivity would have been greater in homeotherms relative to poikilotherms since the former can withstand lower temperatures and thus disperse more easily across an elevational gradient.…”

“…While the EC-MA was largely formed in the Late Eocene (38–33 Ma), climatic fluctuations continued and were especially strong during the Pleistocene (Flantua et al, 2019). The cooling in the Pliocene and subsequent Pleistocene climate oscillations likely created a ‘flickering connectivity’ (Flantua et al, 2019) between lowland populations east and west of the EC-MA, and the connectivity would have been greater in homeotherms relative to poikilotherms since the former can withstand lower temperatures and thus disperse more easily across an elevational gradient. Thus, environmental variation, not geology, recently separated lineages on either side of the EC-MA.…”