Factors determining species richness patterns of breeding birds along an elevational gradient in the Horn of Africa region

Abstract

Aim To document the species richness patterns of breeding birds along elevational gradients and explore its drivers in the Horn of Africa region. Location Horn of Africa region. Taxon Breeding birds. Methods Distributional data for breeding birds were collected. Elevational distribution data were extracted, interpolated, and assembled for all birds, passerines, and nonpasserines. In order to tease apart how different environmental factors contributed to the variation in species richness, we found it is necessary to divide the area into four subregions with different climatic regimes and topographic structure, namely western slope, eastern slope, wet side, and dry side. Then, the species richness in each 100‐m elevational band was counted along the elevational gradients of each subregion. Pearson's correlation analyses and ordinary least squares (OLS) regressions were used to examine the relationships between species richness and factors. Results The variation in species richness followed hump‐shaped patterns for all subregions, although with peak values at different elevations. The bird species groups on the western and eastern slopes showed low and high plateaus with mid‐elevation peaks, respectively, but very low species diversities at the highest elevations. Species richness was significantly correlated with temperature range and productivity in each subregion. The temperature range, area, and productivity explained 82% of the species richness variations for all birds on the western slope. Main conclusions The separate analyses of four area subdivisions provide strong indications of how various factors interact. Productivity and temperature range were the major driving factors for shaping the richness patterns, but deviations from expected patterns suggest modifying roles of mist formation zones in the valleys that deeply intersect the large highlands in the west and rich riparian vegetation where water from cool and humid environments at high elevation reaches lower elevations in the arid east. Conservation is recommended in each subregion based on the elevational richness scenarios.

Afrotropical montane birds experience upslope shifts and range contractions along a fragmented elevational gradient in response to global warming

“…Most research on elevational range shifts of bird species over time in the tropics has been conducted in the Neotropics [13,16,25,33] and Southeast Asia [15,26,34]. There has been relatively little research in the Afrotropics (but see: [35][36][37][38]). This is salient because most montane forests in Africa are isolated from one another and continuous elevational gradients have often received incomplete protection [39,40].…”

Elevational patterns of species richness and community structure of understorey birds in an East African montane forest

“…Montane areas host over half of the world's biodiversity hotspots (Guo et al., 2013; Lomolino, 2001; Rahbek & Graves, 2001; Sam et al., 2019), and many mountain ranges in the tropics have a high conservation value owing to high levels of endemism, bird evolution and ecological specialisation (Abebe et al., 2019; White & Bennett, 2015). Understanding the species dynamics in montane ecosystems is crucial for contemporary conservation in the face of a warming climate (Heller & Zavaleta, 2009), yet this has been a main challenge for biographers, ecologists and conservationists (Abebe et al., 2019; Marchese, 2015). Fluctuations in climate conditions are expected to intensify due to increasing temperatures (IPCC, 2021), and this has generated increased research interest on variation of species diversity with elevation in the last few decades (Dillon & Conway, 2021; McCain & Colwell, 2011).…”

“…Additionally, due to high rates of forest degradation in tropical regions (Laurance et al., 2011), biodiversity is severely threatened (Eglington & Pearce‐Higgins, 2012; Vieira et al., 2008). Besides temperature, a variety of other factors including precipitation (Abebe et al., 2019; Santillán et al., 2018), vegetation cover (Forero‐Medina et al., 2011; Jankowski et al., 2013; Kittelberger et al., 2021; Santillán et al., 2018), habitat quality (Forero‐Medina et al., 2011; Freeman et al., 2018), resource availability (Forero‐Medina et al., 2011; Santillán et al., 2018), interspecific competition (Jankowski et al., 2013; Lenoir et al., 2010) and evolutionary history (Santillán et al., 2018) may also exert strong influence on the distributional limits and diversity of birds along elevational gradients. Montane ecosystems are important because they are viewed as a potential future refugia for species displaced by a changing climate, while at the same time supporting habitat types considered at highest risk of decline due to global warming (Dillon & Conway, 2021).…”

White-rumped Vulture’s Habitat Suitability Prediction using MaxEnt in Arunachal Pradesh

“…The suitability of the habitats for vultures was greatly influenced by land use-land cover (forest and waterbodies), isothermality, and precipitation seasonality in Madhya Pradesh [29]; altitude, mean temperature of the wettest quarter, precipitation of the warmest quarter, and mean diurnal range in Nepal [30]. Habitat suitability or distribution of WRV and other vultures were strongly influenced by the food availability [31][32][33], elevation [34,35], climate [35][36][37][38], vegetation [39,40], and land use pattern [29,40,41].…”