Padrões de coocorrência entre espécies de plantas invasoras: a hipótese do colapso invasor se mantém em gradiente de estresse?

Abstract

Invasive exotic species represent one of the main threats to global biodiversity, altering ecological dynamics and affecting the structure of plant communities. The Invasional Meltdown Hypothesis (Invasional Meltdown Hypothesis - IMH) suggests that facilitative interactions among exotic species can intensify invasion processes, while the Stress Gradient Hypothesis (Stress Gradient Hypothesis-SGH) proposes that positive interactions betweenplants increase in more stressful environments. However, the relationship between thesehypotheses has not been explored. This study investigated co-occurrence patterns amonginvasive exotic species along a climatic and soil fertility gradient, assessing whether variations in these environmental factors modulate interactions among invaders. To this end,data collection was conducted on exotic woody vegetation in ten areas distributed along thecoast of Ceará, Brazil, with systematic records of invasive species occurrence and soil macronutrient analysis. Co-occurrence patterns were evaluated using the Cscore index, and generalized linear models (GLM) were applied to test the influence of environmentalgradients on species coexistence. The results indicated that co-occurrence among invasivespecies predominantly followed a random pattern, with no strong segregation or facilitationamong species, and there was no significant effect of climatic variables on the structure of theinvasive community. However, soil fertility showed a marginally significant negativerelationship with the Cscore index, suggesting that environments with lower fertility maypromote greater differentiation among exotic species. These findings indicate that theinteraction between IMH and SGH may be more complex than anticipated, depending onother biotic factors and invasion histories. Thus, this study contributes to the understanding ofthe dynamics of biological invasions and highlights the need for future investigations thatincorporate larger sampling efforts and complementary approaches to better comprehendthese patterns.