Demographic processes limit upward altitudinal range expansion in a threatened tropical palm

Abstract

Understanding the factors that determine species’ range limits is a key issue in ecology, and is fundamental for biodiversity conservation under widespread global environmental change. Elucidating how altitudinal variation affects demographic processes may provide important clues for understanding the factors limiting current and future species distributions, yet population dynamics at range limits are still poorly understood. Here, we tested the hypothesis that lower abundance at a species’ upper altitudinal range limit is related to lower vital rates. We compared the dynamics of two populations of the tropical palm Euterpe edulis, located near and at the edge of its altitudinal limit of distribution in the Brazilian Atlantic Forest. Data from four annual censuses, from 2012 to 2015, were used. We used matrix population models to estimate asymptotic population growth rates and the elasticity values for the vital rates of the two populations of E. edulis. Life table response experiments were used to compare population performance by measuring the contribution of each vital rate to population growth rates. Population growth rates were not significantly different from one in either population, indicating that both populations were stable during the study period. However, the abundance of all ontogenetic stages was lower at the altitudinal range limit, which was related to decreases in some vital rates, especially fecundity. Additionally, there were higher elasticity values for the survival of immatures and reproductive individuals, compared to all other vital rates, in both populations. Synthesis. Our results show that even a small‐scale environmental variation near range limits is sufficient to drive changes in the demography of this threatened palm. A minor increase in elevation approaching the limit of altitudinal distribution may reduce environmental suitability and affect population vital rates, thus contributing to setting upper altitudinal range limits for plants.

Altitude‐mediated soil properties, not geography or climatic distance, explain the distribution of a tropical endemic herb

“…However, we found a strong direct positive effect of soil nutrients on plant density. Several studies showed that plant density decreases with altitude due to temperature variation and metabolic limitations at higher elevations (Angert, 2006;Souza et al, 2018). Instead of temperature gradient, for T. atacorensis, soil macronutrients variation along elevational gradient drives plant density.…”

GEOGRAPHIC DISTRIBUTION OF THE THREATENED PALM Euterpe edulis Mart. IN THE ATLANTIC FOREST: IMPLICATIONS FOR CONSERVATION

“…This pattern of variation in climatic suitability is probably linked to the physiological requirements of E. edulis for germination and growth, especially a low tolerance to dry conditions (Andrade 2001, Gatti et al 2014, which are relatively more common in Seasonal forests than in Ombrophilous forests (IBGE 1993). In addition, the low tolerance of E. edulis to low temperatures could explain the absence of this species above 1500 m altitude (Gatti et al 2008, Roberto & Habermann 2010, Souza et al 2018.…”

“…In the Brazilian Atlantic Forest, this species has a wide latitudinal distribution, from Rio Grande do Norte to Rio Grande do Sul states, and from seal level up to around 1000-1400 m a.s.l. (Henderson et al 1995, Souza et al 2018. Euterpe edulis occurs in different vegetation types within the Atlantic Forest, including Ombrophylous, Deciduous, and Restinga forests (Henderson 1995, Gatti et al 2011.…”

Micro‐ or macroscale? Which one best predicts the establishment of an endemic Atlantic Forest palm?

“…Since initial establishment is a critical phase of plant life (Donohue et al, 2010;Spindelböck et al, 2013), germination success in areas with the presence of adult individuals of the same species can be seen as a form of validation of the model. Therefore, it is important to highlight the mortality between seedling to adult stages (Souza, Portela, & De Mattos, 2018) were not evaluated here. So, there is a synergistic interaction between micro-and macroscale conditions that influence both initial establishment and older stages.…”