Biological activities as patchiness driving forces in wetlands of northern Belize

Abstract

Patchiness in wetlands is a common and well documented phenomenon. Oligotrophic wetlands of northern Belize display noticeable vegetation heterogeneity at both large and small scales. In this paper, we document the small scale patches in herbaceous wetlands, describe differences between patches and surrounding wetland habitats and explain patch formation and sustenance.We conducted a survey of patches and confirmed their occurrence by spatial analysis. Patches were distinguished from a surrounding wetland by denser and taller vegetation, higher amount of empty snail shells and elevated soil phosphorus (P). Plants in patches had higher tissue nitrogen (N) and P content and there was also higher total N and P per m2 incorporated in plant biomass. In terms of stable isotopes, plants in patches were enriched in 15N; patch soils were depleted in 13C.Observations of focal individuals of Aramus guarauna, limpkin, a wading bird feeding almost exclusively on snails, revealed the origin of the snail shell piles frequently found in patches. An adult limpkin captured on average 18 snails daily, of these 80% were handled in patches and birds often repeatedly used the same patch.Experimental patch creation by adding chicken manure or P to 1 m2 plots resulted in higher and denser vegetation with values increasing in order: control, P, manure plots. The effect was significant at both experimental locations six months after the treatment and at one location even 40 months after the treatment.We present a simple mechanistic explanation for nutrient redistribution in wetlands and their eventual accumulation in patches. Both nutrient and isotopic differences result from animal input into patches, e.g. bird droppings or prey remnants. Foraging activity of Aramus guarauna is most likely responsible for patch formation. A positive feedback (repeated use of a suitable patch) is apparently the mechanism sustaining patches in these marsh environments.