The flickering connectivity system of the north Andean páramos

Suzette G.A Flantua,Aaron O'Dea,Henry Hooghiemstra,Renske E Onstein,Catalina Giraldo

doi:10.1111/jbi.13607

Abstract

AbstractAimTo quantify the effect of Pleistocene climate fluctuations on habitat connectivity across páramos in the Northern Andes.LocationNorthern Andes.MethodsThe 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 upper forest line 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 estimate their connectivity to provide insights into the role of topography in biogeographical 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 topographical configuration. The flickering connectivity system of the páramos uncovers the dynamic settings in which evolutionary radiations shaped the most diverse alpine biome on Earth.

Highlights

We find support for the hypothesis that this system with fluctu‐ ating, highly variable connectivity in spatial and temporal dimension is unique for each mountain range of the Northern Andes (Figure 1)
We present a pollen record‐based biogeographical model for the páramo biome spanning the northern Andes (Venezuela, Colombia and Ecuador) over the last 1 million years (Myr)
Our analysis shows that páramos on all moun‐ tain ranges underwent frequent alterations between fragmented and connected configurations (Figures 4 and 5), but the estimated degrees and amount of connectivity varied among mountain ranges (Figure 6)

Summary

| MATERIAL AND METHODS

The Northern Andes (ca. 448,000 km2) covers parts of Venezuela, Colombia and Ecuador (Figure 2a), and can be partitioned into six principal mountain ranges or ‘cordilleras’ (Figure 2c), namely the Sierra Nevada de Santa Marta (SNSM), Cordillera de Mérida, Eastern, Central and Western Cordillera and the Ecuadorian Cordilleras. Our estimations on the spatial and elevational extent of ancient páramos and their connectedness at different times in the past reveals that páramos underwent frequent spatial alterations be‐ tween fragmented and connected spatial configurations, but the exact patterns were highly dependent on mountain chain topogra‐ phy The páramos of the SNSM and the Western Cordillera endured the high‐ est degree of rates of change in fragmentation of all ranges In the latter, páramo habitats are estimated to have often completely dis‐ appeared. Considering only the frequency in the distribution of data (Figure 6b), the Ecuadorian Cordillera and the SNSM stand out for their relatively small within‐mountain range variation in connectiv‐ ity, compared to the Eastern and Central Cordillera (similar patterns) and the Western Cordillera.

| DISCUSSION

Findings

| CONCLUSIONS