Ecology of standing waters

Community assembly and food web interactions across pond permanence gradients

Trade-offs between resisting biotic interactions and physical stress are often thought to structure communities along environmental gradients. However, the importance of these trade-offs in community assembly is likely to be affected by the predictability of physical stressors and spatiotemporal variation biotic interactions.

As part of his PhD research, Hamish Greig (see Greig 2008, pdf 150kb) investigated community dynamics in ponds across an unpredictable drying regime (pond permanence) in Canterbury, New Zealand (Fig. 1), and in snowmelt-fed ponds in the Colorado Rockies with predictable drying and filling regimes.

Fig. 1 Landscape mosaic of temporary and permanent ponds on the Blackwater Moraine, Canterbury, New Zealand.

In New Zealand, community composition and species richness were strongly influenced by pond permanence. However, species in temporary ponds were a nested subset of generalists that were also found in permanent ponds (Fig. 2), rather than a unique assemblage of temporary pond specialists Wissinger et al. 2009 (pdf, 200kb).

Figure 2. Venn diagram of species overlap from a regional pool of 106 taxa in 29 ponds grouped by relative permanence: temporary = early season drying each year; semipermanent = late-season drying most years; permanent = does not dry. Numbers are pooled counts of species across all ponds in a given category.

Subsequent experiments (Fig. 3) indicated predator impact decreased with pond permanence, partially due to the foraging suppression of predatory invertebrates in permanent ponds by fish.

Figure 3. Experimental tanks investigating interference among predatory invertebrates and fish.

Weak predation in permanent ponds combined with unpredictable drying regimes likely selected for generalist traits, and resulted in community assembly being driven by a gradient of drying stress rather than a trade-off between biotic interactions and drying.

Additional field experiments in New Zealand (Fig. 4) indicated predator impact increased over time in late drying temporary ponds but not in permanent ponds, possibly leading to seasonally variable habitat properties within and between habitats in the landscape (Fig 5).

Experiments in Colorado ponds indicated similar shifts in predator impact led to predictable windows of weak predation in late drying ponds that were exploited by vulnerable species with rapid development. Thus, seasonal shifts in biotic interactions may lead to broader distributions of species with specialized traits, and greater within-habitat (α) diversity. Overall, my results suggest considering the predictability of disturbance regimes and spatiotemporal variation in biotic interactions will enhance the understanding and subsequent management of communities in heterogeneous landscapes.  

People involved in this project

University of Canterbury
Hamish Greig
Angus McIntosh

Allegheny College
Scott Wissinger

Publications

Greig 2008. Community assembly and food web interactions across pond permanence gradients. PhD thesis, University of Canterbury (pdf, 150kb)
Wissinger, Greig & McIntosh 2009. Absence of species replacements between permanent and temporary lentic communities in New Zealand. Journal of the North American Benthological Society 28:12-23 (pdf, 200kb)