Context‐dependent biotic interactions control plant abundance across altitudinal environmental gradients

Abstract

Many biotic interactions influence community structure, yet most distribution models for plants have focused on plant competition or used only abiotic variables to predict plant abundance. Furthermore, biotic interactions are commonly context‐dependent across abiotic gradients. For example, plant–plant interactions can grade from competition to facilitation over temperature gradients. We used a hierarchical Bayesian framework to predict the abundances of 12 plant species across a mountain landscape and test hypotheses on the context‐dependency of biotic interactions over abiotic gradients. We combined field‐based estimates of six biotic interactions (foliar herbivory and pathogen damage, fungal root colonization, fossorial mammal disturbance, plant cover and plant diversity) with abiotic data on climate and soil depth, nutrients and moisture. All biotic interactions were significantly context‐dependent along temperature gradients. Results supported the stress gradient hypothesis: as abiotic stress increased, the strength or direction of the relationship between biotic variables and plant abundance generally switched from negative (suggesting suppressed plant abundance) to positive (suggesting facilitation/mutualism). For half of the species, plant cover was the best predictor of abundance, suggesting that the prior focus on plant–plant interactions is well‐justified. Explicitly incorporating the context‐dependency of biotic interactions generated novel hypotheses about drivers of plant abundance across abiotic gradients and may improve the accuracy of niche models.

Interspecific competition constrains local abundance in highly suitable areas

“…Assuming that competition is stronger within communities with more similar species, richness of potential competitors is expected to reduce the relative abundance of a species via resource depletion and density‐dependent regulation (Meszéna et al , Soberón ). However, the strength of biotic interactions can be context‐dependent on the environmental conditions (Zambrano et al , Lynn et al ). For instance, the effects of interspecific competition can be stronger under stressful environments (Hart and Marshall ).…”

Macroecological context predicts species' responses to climate warming

“…Novel biotic interactions (e.g., competitors) in the warmer and/or wetter environments likely increase the extinction probability and abundance declines of cold niche species. Distribution modeling suggests that the negative relationship between competition and abundance for a species can intensify in warmer and wetter areas (Lynn et al, 2019; Mod et al, 2014). This is bolstered by experimental evidence that novel competitors in warmer/low elevation plant communities lower survival probability, growth, and reproduction of focal species more than competitors found in their home communities in the same novel climate (Alexander et al, 2015).…”

Asociaciones entre las características reproductivas y la abundancia en Gymnocalycium quehlianum (Cactaceae) a lo largo de un gradiente altitudinal

“…Particularmente, se esperaba un mayor peso de las semillas en los sitios donde la especie fuera más abundante (Leishman et al 2000). En este sentido, es posible que otras variables, como parámetros poblacionales (e.g., tasas de fecundidad, probabilidades de supervivencia de las plántulas), estén relacionadas a los patrones de abundancia (Lynn et al 2019). Tampoco es posible descartar que algunas interacciones biológicas, tanto positivas como negativas, como la polinización, dispersión y competencia con otras especies, intervengan sobre los patrones de abundancia (Mangan et al 2010, Lynn et al 2019.…”

“…Los ambientes montañosos presentan una riqueza de especies muy alta en relación con el área que poseen (Rahbek et al 2019), razón por lo cual son áreas muy importantes para la conservación de la biodiversidad (Perrigo et al 2020). En estos ambientes las especies pueden presentar importantes rangos de distribución altitudinal , Bauk et al 2015 variando su abundancia local a lo largo de los gradientes (Siebert 2005, Lynn et al 2019. Entender los factores que regulan la abundancia de las especies a lo largo de gradientes altitudinales es importante tanto desde un punto de vista teórico (Lynn et al 2019), como aplicado, ya que permiten evaluar como el cambio climático podría afectar la distribución y abundancia de las especies en estos ambientes (Illoldi-Rangel et al 2012, Pacifici et al 2015.…”

“…El rango altitudinal de una especie se relaciona con el nicho climático de la misma (Vázquez 2005, Polechová & Storch 2008, mientras que la abundancia a lo largo de dicho rango estará moldeada por diferentes factores, como los microambientes o el contexto biológico (Lynn et al 2019). Si bien existen numerosos estudios que han analizado patrones de riqueza de especies en gradientes altitudinales (Guerrero et al 2011, Gong et al 2019, muy pocos se han detenido en analizar patrones de abundancia de especies particulares (Siebert 2005) y los factores que afectan dichos patrones (Lynn et al 2019).…”