Disturbance from pond management obscures local and regional drivers of assemblages of primary producers

Abstract

Summary Ponds have significant conservation value due to their potentially high contribution to local and regional diversity. However, most ponds are located in anthropogenically influenced areas, and their biodiversity is constantly threatened by human activities. Thus, knowledge of the effect of pond management on biodiversity is essential for designing effective conservation strategies. Here, we study the main drivers of diversity of three functional groups of primary producers (phytoplankton, filamentous green algae and submerged macrophytes) in 87 ponds distributed across a large region (c. 90000 km2) in Southern Spain. We hypothesised that spatial effects would increase with increasing propagule size. However, given the regional extent of the study, we anticipated that both spatial and environmental controls would be significant. We determined α‐, β‐ and γ‐components of biodiversity for each functional group and pond type (embankment ponds, excavated ponds and artificial ponds) and assessed the influence of environmental and spatial drivers on diversity with generalised additive models (GAMs). Redundancy analyses (RDAs) with variation partitioning were used to determine the relative contribution of environmental and spatial predictors of the community assembly. Spatial variables were calculated by applying distance‐based Moran's eigenvector maps (db‐MEM). Both α‐ and β‐diversities of phytoplankton and filamentous green algae varied significantly with pond type. Generally, environmental predictors of diversity were more important than spatial variables. Assemblage structure was controlled by water chemistry and eutrophication, with a marked influence of pond type. Spatial variables included broad‐scale variation for the three groups of primary producers, which were also strongly influenced by the management regime. Limited management activities, as occurs at embankment ponds, promoted the local richness of phytoplankton and contributed importantly to the regional diversity of macrophytes. Moreover, the relative contribution of environmental and spatial variables was similar between embankment ponds and natural ecosystems, that is, dispersal limitation increasing with propagule size. Excavated and artificial ponds also contributed importantly to regional diversity by enhancing phytoplankton and filamentous green algal β‐diversity. However, spatial patterns in the latter pond type did not meet our expectations, most likely due to the intensive disturbance from pond management hampering the development of macrophytes.

Water depletion drives plant succession in farm ponds and overrides a legacy of continuous anthropogenic disturbance

“…Furthermore, farm ponds created by constructing small dams in streams (Akasaka & Takamura , ; Gallego et al. ) may retain water even after being abandoned. For the conservation of ecosystem function at a regional scale, it is indispensable to clarify the relationship between the distribution of ponds in which water depletion is likely to occur after abandonment and the distribution of functionally unique species.…”

“…; Gallego et al. ; see Appendix for a summary of these variables). We obtained data on two management status variables (years since abandonment and frequency of mowing on the bank each year) and water source type by interviewing managers of the surveyed ponds and local farmers ( n = 100) from mid‐Jul to mid‐Aug 2014.…”

“…These larger ponds, therefore, appear to be able to retain water and habitats suitable for helophytes and macrophytes even after being abandoned, but the plant community in smaller ponds is more likely to undergo larger functional changes due to water depletion. Furthermore, farm ponds created by constructing small dams in streams (Akasaka & Takamura 2011Gallego et al 2014) may retain water even after being abandoned. For the conservation of ecosystem function at a regional scale, it is indispensable to clarify the relationship between the distribution of ponds in which water depletion is likely to occur after abandonment and the distribution of functionally unique species.…”

“…We collected data on 16 environmental variables that might determine the functional richness in a pond: management status (two variables), physical conditions (six), topographic conditions (two), surrounding land-use type (five) and water source type (one) (Akasaka et al 2010;Akasaka & Takamura 2011;Alahuhta et al 2013;Gallego et al 2014; see Appendix S2 for a summary of these variables). We obtained data on two management status variables (years since abandonment and frequency of mowing on the bank each year) and water source type by interviewing managers of the surveyed ponds and local farmers (n = 100) from mid-Jul to mid-Aug 2014.…”

Quantifying the relative importance of natural variables, human disturbance and spatial processes in ecological status indicators of boreal lakes

“…aquatic plants disperse via wind, water and waterfowl, whereas fish rely only on hydrological connections (Shurin et al, 2009;Hajek et al, 2012). Multiple taxonomic groups are increasingly used to assess status of freshwaters; however, the importance of spatial processes have only recently been taken into account in the bioassessment (Gray and Arnott, 2011;Anas et al, 2014;Gallego et al, 2014;Siqueira et al, 2014).…”