Effects of topographic factors on distribution of cacti along an elevation gradient in Brazilian Caatinga

Abstract

The Cactacea family comprises 128 genera and 1450 species with predominantly neotropical distribution. Cacti are commonly found in arid and semi-arid regions and have great ecological relevance due to their interactions with animals and other groups of plants. Abiotic interactions, such as topography, altitude, rainfall, temperature and soils, also influence the composition and distribution of cacti. The objective of the present study was to assess patterns of species composition and distribution for cacti along an elevation gradient in Brazilian Caatinga vegetation. Four transects (composed by 25 plots of 100 m² each) were established at each of two mountain sites. The topographic variables of elevation, slope, rockiness and soil depth were evaluated to determine if they affect the distribution of richness and abundance of cacti along the elevation gradient using Spearman's (rs) correlation coefficient. A total of 554 individuals of five cacti species (Pilosocereus gounellei, Pilosocereus pachycladus, Tacinga palmadora, Tacinga inamoena and Melocactus zehntneri) were sampled. Cacti richness and abundance were found to be negatively correlated with elevation, slope and rockiness, and positively correlated with soil depth (p<0.05). All species exhibited aggregate spatial distribution patterns, which may be related to different environmental conditions produced by interactions among topographic variables (slopes, rockiness and soil depth), that synergistically influence the patterns of species richness and abundance along the elevation gradient.

Identifying the multiple drivers of Cactus diversification

“…However, rapid lowland speciation has also been documented in woodcreepers (Weir and Price, 2011). Furthermore, higher elevations have been associated with a slower tempo of evolution, in rates of molecular evolution (Bleiweiss, 1998) (Diniz et al, 2021), its impact on diversi cation rate is underexplored. We nd a signi cant but weak role for slope in predicting speciation rate, and recover a negative sigmoidal relationship (Figure 3).…”

Phylogenetic diversity and structure in moist and dry upland forests in the semi-arid region of Brazil

“…As an additional criterion, we included communities belonging to the Atlantic Forest and Caatinga domains in the study, which are in locations that presented a minimum elevation of 600 m within the semi-arid region. We used this criterion because DUF (Silva et al, 2014;Moro et al, 2016;Lopes et al, 2017;Ramos et al, 2020;Diniz et al, 2021) and MUF (Tabarelli and Santos, 2004;Santos et al, 2007b;Queiroz et al, 2017;Marques et al, 2021) are intrinsically related to features such as plateaus, flat-topped hills, mountain ranges, low mountains, inselbergs, and peaks.…”

“…The most influential abiotic filters contributing to habitat diversification and shaping biodiversity patterns in upland ecosystems encompass temperature, precipitation, and soil properties (Zhang et al, 2016;Chun and Lee, 2018;Sabatini et al, 2018;Luo et al, 2019;Zhu et al, 2019;Ohdo and Takahashi, 2020). In the Neotropics, these abiotic filters stand out as significant drivers of shifts in taxonomic diversity patterns among different plant communities established in uplands, such as Andean forests (Cuesta et al, 2017), Tepuis (Campos et al, 2022a), Inselbergs (Pinto-Junior et al, 2020), Páramos (Campos et al, 2018;Neri et al, 2017), and Caatinga Uplands (Santos et al, 2007a;Ramos et al, 2020;Diniz et al, 2021). Recent studies also indicate that these abiotic filters have a strong relationship with phylogenetic diversity and structure patterns observed in Neotropical upland ecosystems (Mattos et al, 2019;Campos et al, 2021Campos et al, , 2022bCisneros et al, 2021).…”

“…To address this gap, the present study investigates two co-occurring upland ecosystems in the semi-arid region: the Serras de Caatinga (dry upland forests -DUF) and the Brejos de Altitude (moist upland forests -MUF). The DUFs harbor communities within the phytogeographic domain of the Caatingas (Silva et al, 2014;Moro et al, 2016;Lopes et al, 2017;Ramos et al, 2020;Diniz et al, 2021). In contrast, the MUFs consist of islands of moist vegetation belonging to the Atlantic Forest domain (tropical moist forest), also present in elevated areas of the semi-arid region (Tabarelli and Santos, 2004;Rodal and Nascimento, 2006;Santos et al, 2007b;Rodal et al, 2008;Queiroz et al, 2017;Marques et al, 2021).…”

Identifying the multiple drivers of Cactus diversification

“…Diversification rates are fastest in species with larger growth forms and derived pollination syndromes (bat, bird and moth pollination (Schlumpberger, 2012). However, there are a range of other potential drivers of diversification suggested by correlations with biodiversity, including geographic distribution (Majure et al, 2012;Hernández-Hernández et al, 2014;Pillet et al, 2022), elevation (Luebert and Weigend, 2014), global temperature (Silva et al, 2018), chromosome number (Lopes et al, 2021), edaphic properties (Ruedas et al, 2006) and climatic variables recently associated with endemism (Trabuco Amaral et al, 2022). Additionally, we do not know whether Cacti are be influenced by variables known to contribute to broad-scale patterns of diversification in succulents, or angiosperms more generally, including topographic complexity (Verboom et al, 2015) and geographic range size (Hernandez-Hernandez and Wiens, 2020).…”