Commonness, rarity, and oligarchies of woody plants in the tropical dry forests of Mexico

Abstract

We assessed woody plant communities in two widely separated forests in the tropical dry forest (TDF) biome of Mexico for evidence of similar patterns of species commonness and rarity. We used belt transects laid out along contour lines (i.e., constant elevation) and stratified across elevation gradients at sites in Jalisco and Oaxaca to sample woody plant species diversity, abundance, relative frequency and basal area. We assembled a combined species list and compared species found in both sites (shared) to species found in only one site, assessing whether the most and least common species at a site tended to be shared or unshared. Of the 8242 individuals sampled, 370 species or morpho‐species were identified, with 222 species recorded at the Jalisco site and 270 at the Oaxaca site—122 (33%) species were shared across sites. Abundance, frequency and basal area of shared species were greater on average than for unshared species, and were positively correlated across sites. A subset of 68 shared species (18%) accounted for over half of all individuals encountered at the two sites. Species in the most common quartile were more likely to be shared than expected by chance, while species in the least common quartile were less likely. A genus‐level analysis found similar patterns. Our findings suggest that the TDF of Pacific coast Mexico shows evidence of widespread dominance by a small subset of species. These findings have potentially important implications for predicting species composition, understanding the role of oligarchic species in ecological processes, and conserving rare species.

Disentangling the environmental heterogeneity, floristic distinctiveness and current threats of tropical dry forests in Colombia

“…We also found that the most widespread dry forest species were generalists that are favored by forest disturbance and early successional stages (appendix table A2), as reported by previous studies (Uribe et al 2001, López-Camacho et al 2012, Castellanos-Castro and Newton 2015, Williams et al 2017 for other TDFs (Newbold et al 2014), indicating the incipient successional status of dry forests at the regional level (Derroire et al 2016). Furthermore, we found an introduced invasive species (V. farnesiana) among the most common species of TDFs throughout the country, suggesting that TDFs are also highly susceptible to invasion (Pizano et al 2014a).…”

“…In fact, environmental and soil factors explained 13% of the variation in plant species composition ( figure 2(c)). Similar to other dry forests in the Neotropics, we found high species turnover for both across and within regions (Linares-Palomino et al 2011, Neves et al 2015, DRYFLOR et al 2016, Williams et al 2017, as well as high levels of endemism across TDF regions. Floristic composition in the Caribbean appears to be correlated with soils with a high pH and high bulk density, high mean annual temperature, and the longest dry season ( figure 2(c)).…”

“…However, these forests vary significantly in rainfall seasonality (Murphy and Lugo 1986, Gentry 1995, Murphy and Lugo 1995, Pennington et al 2009, soil nutrients, soil texture (Peña-Claros et al 2012), soil water storage (Neves et al 2015), frost (Pennington et al 2006) and altitude (Gentry 1995). Correspondingly, TDF plants have been modeled as metacommunities historically adapted to dry conditions (Pennington et al 2009) with high species turnover and endemism as a result of historical fragmentation, dispersal limitation (Linares-Palomino et al 2011, Neves et al 2015 and environmental controls (Neves et al 2015, Williams et al 2017.…”

Climate risk on two vegetation axes—Tropical wet‐to‐dry and temperate arid‐to‐moist forests

“…The lowland Isthmus of Tehuantepec, which represents the border between the North American and Central American biogeographical provinces, is influenced mostly by these weather patterns, neotropical climate, and biogeography. As such, the vegetation in these forests is frequently dominated by lineages of South American or Central American‐Caribbean origin (for representative species lists, see Boyle, ; García‐Mendoza & Meave, ; Salas‐Morales, Saynes‐Vasquez, & Schibli, ; Williams, Trejo, & Schwartz, ).…”

“…The major temperate and tropical axis vegetation types are projected to experience similar increases in the percentage of their area that shifts into the "high" and "very high" exposure categories in both the near-future (9.5% and 11%, respectively) and end-century (30% and 32%, respectively) periods, based on the five-model average. The differences in the percentage of cells projected to move into the NA category are more striking, with a much higher percentage of NA cells projected for the tropical axis compared to the temperate axis in both the near-future (1.1% vs. 0.067%) and end- Boyle, 1996;García-Mendoza & Meave, 2012;Salas-Morales, Saynes-Vasquez, & Schibli, 2003;Williams, Trejo, & Schwartz, 2017).…”