Cascading community and ecosystem consequences of introduced coconut palms (Cocos nucifera) in tropical islands

Abstract

Biological invasions are a pervasive and dominant form of anthropogenic disturbance. However, we seldom have the opportunity to evaluate the long-term, indirect, and often slow-moving cascading effects of invasions at the community and ecosystem scale. Here we synthesize the collective knowledge from 10 years of study on the influence of the deep historical introduction of coconut palms (Cocos nucifera L.) across a series of islets at Palmyra Atoll. Through a suite of pathways, we find this palm drives near-complete ecosystem state change when it becomes dominant. Abiotic conditions are transformed, with major soil nutrients 2.7-11.5 times lower and water stress 15% elevated in palm-dominated forests compared with native forest. Faunal communities are likewise dramatically altered, not only in composition but also in behavior, body size, and body condition. Biotic interactions, including herbivory rates, palatability, and seed predation, are likewise changed. Cumulatively, these changes transform food webs, leading to dramatically shortened and simplified food chains in invaded ecosystems. Many of these changes appear to create slow-acting feedback loops that favor the palm at the expense of native species. Given the widespread nature of this historical introduction, many island and coastal regions of tropical oceans may be similarly transformed.

Invasive rat eradication strongly impacts plant recruitment on a tropical atoll

“…High abundances of C . nucifera have been shown to cause cascading ecosystem impacts including changes in water availability, soil nutrient content, plant and animal community composition, and changes in the behavior, size, and body condition of island fauna [ 45 ]. If uncontrolled, non-native C .…”

“…The coconut palm, C . nucifera , was first spread throughout the Pacific Ocean by Austronesian voyagers over 1500 years ago, then by early European explorers, and most recently by early European agricultural entrepreneurs for copra production [ 44 , 45 ]. On islands where they have been introduced, coconut palms often form monodominant stands and have been shown to directly compete with P .…”

“…grandis for water resources [ 46 ]. Cocos nucifera was likely introduced to Palmyra Atoll within the past 1500 years [ 44 , 47 ] with abundance increasing between 1850 and 1970 due to small-scale cultivation efforts [ 45 ]. Rattus rattus can be an important predator of coconut palm seeds and seedlings (by consuming the sprouting apical meristem); these behaviors may have partially controlled the recent expansion of this invasive plant further into the atoll’s remaining native species forest stands [ 33 , 48 ].…”

Stable isotope analysis as an early monitoring tool for community‐scale effects of rat eradication

“…The atoll is composed of 25 smaller islets that vary in productivity due to variation in the density of nesting seabirds and their guano subsidies (Young et al ). This gradient drives cascading changes in community composition (Young et al ) with potential impacts on crab ecology. To capture the range of variability, we chose to sample one high‐ and one low‐productivity islet (Eastern and Paradise Islets; Young et al ).…”

“…Fish and Wildlife Service ). However, changes in these responses are likely to both influence and be influenced by other shifts in the atoll community (Young et al ).…”