DOI: 10.6078/d14x3z
title: In transition: avian biogeographic responses to a century of climate change across desert biomes

description: Transition zones between biomes, also known as ecotones, are areas of
 pronounced ecological change. They are primarily maintained by abiotic
 factors and disturbance regimes that could hinder or promote species range
 shifts in response to climate change. We evaluated how climate change has
 affected metacommunity dynamics in two adjacent biomes and across their
 ecotone by resurveying 106 sites that were originally surveyed for avian
 diversity in the early 20th century by Joseph Grinnell and colleagues. The
 Mojave, a warm desert, and the Great Basin, a cold desert, have distinct
 assemblages and meet along a contiguous, east-west boundary. Both deserts
 substantially warmed over the past century, but the Mojave dried while the
 Great Basin became wetter. We examined whether the distinctiveness and
 composition of desert avifaunas have changed, if species distributions
 shifted, and how the transition zone impacted turnover patterns. Avifauna
 change was characterized by (a) reduced occupancy, range contractions, and
 idiosyncratic species redistributions; (b) degradation of historic
 community structure, and increased taxonomic and climatic differentiation
 of the species inhabiting the two deserts; and (c) high levels of turnover
 at the transition zone but little range expansion of species from the
 warm, dry Mojave into the cooler, wetter Great Basin. Although both
 deserts now support more drier- and warmer-tolerant species, their bird
 communities still occupy distinct climatological space and differ
 significantly in climatic composition. Our results suggest a persistent
 transition zone between biomes contributes to limiting the redistribution
 of birds, and highlight the importance of understanding how transition
 zone dynamics impact responses to climate change.Transition zones between
 biomes, also known as ecotones, are areas of pronounced ecological change.
 They are primarily maintained by abiotic factors and disturbance regimes
 that could hinder or promote species range shifts in response to climate
 change. We evaluated how climate change has affected metacommunity
 dynamics in two adjacent biomes and across their ecotone by resurveying
 106 sites that were originally surveyed for avian diversity in the early
 20th century by Joseph Grinnell and colleagues. The Mojave, a warm desert,
 and the Great Basin, a cold desert, have distinct assemblages and meet
 along a contiguous, east-west boundary. Both deserts substantially warmed
 over the past century, but the Mojave dried while the Great Basin became
 wetter. We examined whether the distinctiveness and composition of desert
 avifaunas have changed, if species distributions shifted, and how the
 transition zone impacted turnover patterns. Avifauna change was
 characterized by (a) reduced occupancy, range contractions, and
 idiosyncratic species redistributions; (b) degradation of historic
 community structure, and increased taxonomic and climatic differentiation
 of the species inhabiting the two deserts; and (c) high levels of turnover
 at the transition zone but little range expansion of species from the
 warm, dry Mojave into the cooler, wetter Great Basin. Although both
 deserts now support more drier- and warmer-tolerant species, their bird
 communities still occupy distinct climatological space and differ
 significantly in climatic composition. Our results suggest a persistent
 transition zone between biomes contributes to limiting the redistribution
 of birds, and highlight the importance of understanding how transition
 zone dynamics impact responses to climate change.