Community disassembly in ephemeral ecosystems.

Abstract

Community disassembly is the non-random process of progressive species declines and losses. This process is usually studied to determine how various forces extirpate species, such as catastrophic disturbance, species invasions, habitat fragmentation, or unnatural/anthropogenic stressors. However, in ephemeral ecosystems, community disassembly is a natural and repeatable process. While many ephemeral ecosystems are aquatic (vernal pools, playa lakes, rock pools, saline lakes, phytotelmata, etc.), some disassembly patterns are applicable to other ecosystem types, including terrestrial ecosystems. As ephemeral waterbodies near the end of their hydroperiod, certain aspects fundamentally change. These fundamental changes or mechanisms cause visible patterns of community disassembly. Decreasing habitat size eliminates microhabitats and increases encounter rates between organisms, possibly increasing predation and competition. A harshening habitat eliminates low-tolerance species, changes the proportions of specialists/generalists, and forces organisms to acclimate, emigrate, or die. Additionally, ultraviolet light affects more of the water column, eliminating unprotected species. Furthermore, the entire metacommunity is often in similar stages of disassembly and collapses. Many of these mechanisms drive disassembly of terrestrial ephemeral habitats, such as animal carcasses, dung pads, or fungal fruiting bodies. Organisms obligate to ephemeral habitats have evolved to optimize their life history for a rapid life cycle with specific adaptations for themselves or their offspring to survive through the inactive period of the ecosystem. While some disassembly may occur too fast for biotic interactions or compensatory dynamics to be important, organisms undergoing natural disassembly should "expect" it. Thus, predictions of disassembly based on internal or biotic patterns may be more common in natural disassembly scenarios than in human-induced disassembly of permanent ecosystems. Additionally, natural community disassembly should be more predictable and understandable than a permanent community's reaction to a never-before-seen anthropogenic disturbance. Community disassembly is an important ecological component of ephemeral ecosystems. The processes that occur during disassembly shape assemblages over ecologically and evolutionary relevant timescales. Understanding how natural disassembly can feed back to ultimately drive ecosystem structure and function increases our knowledge of fundamental ecology and provides for a new frontier of study.