Predator, prey, and substrate interactions: the role of faunal activity and substrate characteristics

Abstract

Many taxa possess a range of strategies to reduce the risk of predation, including actively seeking suitable refuge habitats; however, the global spread of invasive species may disrupt these behavioral responses. In lotic ecosystems, interstitial spaces in the substrate are important refugia for small organisms. Some predators are ecosystem engineers that exhibit zoogeomorphic agency-the ability to modify the geomorphology of their environment. It is therefore possible that direct ecological effects of predators on prey may be realized through modifications to the prey's habitat, including the availability of refugia, by predators that are zoogeomorphic agents or via external stressors such as fine sediment loading. This study examined three research questions in a mesocosm study across a gradient of sediment-stress treatments: (1) What affects do predators (Pacifastacus leniusculus, invasive crayfish) and prey (Gammarus pulex, amphipods) have on the ingress of fine sediment into gravel substrates and therefore on available interstitial refugia? (2) Do prey taxa seek refuge from (invasive) predators in the form of vertical movement into subsurface sediments? and (3) How does fine sediment ingress influence predator-prey interactions and prey survival through predator avoidance behavior. Here, we provide direct evidence demonstrating that fine sediment ingress into gravel river beds can be facilitated by zoogeomorphic activity with P. leniusculus increasing the infiltration of fine sand particles (but not coarse sand) during foraging activities. Predator-prey interactions were found to be a primary factor mediating zoogeomorphic activity, with the isolation of crayfish from prey (G. pulex) leading to increased fine sand ingress. When present with signal crayfish, G. pulex displayed vertical avoidance behavior, entering subsurface substrates to evade predation by P. leniusculus. Coarse sand treatments resulted in higher predation rates of G. pulex, most likely due to clogging of interstitial pore spaces between gravels limiting the effectiveness of the prey's vertical avoidance behavior strategy. A new conceptual model that captures the interactions between predator, prey, zoogeomorphic processes and habitat availability is presented. This model highlights how predator-prey interactions can be strongly mediated by dynamic bi-directional interactions between organisms and the physical environment they inhabit as ecological and geomorphological processes are intrinsically linked.

Consumer movement dynamics as hidden drivers of stream habitat structure: suckers as ecosystem engineers on the night shift

“…If the spacing between refuge habitats were to exceed typical home ranges observed (e.g. >250 m), divot structures in distant habitats may become less abundant, while local disturbance may be exacerbated (Statzner et al 1996, Mathers et al 2019). However, we suspect that the size of individual home ranges may be at least partially dictated by the availability of food, spacing of refuges and the density of fish within the refuge (Hansen and Closs 2005), so it is unlikely that engineering impacts in natural systems will be limited by distance, except in circumstances where movement potential is restricted.…”

Beneath the surface: Application of transparent super absorbent polymer substrates to track faunal activity within the sediment layer

“…Morphological (e.g. body shape and size) and behavioural traits (habitat affinity and locomotion strategy) of the individual may also alter the behaviour of biota within the sediment layer (Mathers, Hill, et al, 2019;Omesová, Horsák, & Helešic, 2008). There are also documented substrate preferences associated with the body size / life stage of an individual with intra-and inter-specific spatial segregation being observed in many amphipod species (Clinton, Mathers, Constable, Gerrard, & Wood, 2018;McGrath, Peeters, Beijer, & Scheffer, 2007).…”

“…Interstitial pore space between gravel particles represents an important habitat for many organisms (Culp, Walde, & Davies, 1983;Gee, 1982) and often provides a refuge from intra-/ inter-specific predation (Mathers, Rice, & Wood, 2019), and high shear stresses (Franken et al, 2006), in addition to extreme hydrological conditions such as floods or droughts (Dole-Olivier, Marmonier, & Beffy, 1997;Wood, Boulton, Little, & Stubbington, 2010). Deeper subsurface (hyporheic) substrates are essential for maintaining healthy ecosystem functioning and can be spatially extensive (Stanford & Ward, 1988;Williams & Hynes, 1974).…”

“…However, the connectivity and functioning of the hyporheic zone in many river systems is threatened by anthropogenic activities such as impoundment and excessive fine sedimentation, which may modify substrate composition, infilling interstitial spaces, limiting vertical hydrological exchange and eventually disconnecting the hyporheic zone from the surface sediments (Mathers, Millett, Robertson, Stubbington, & Wood, 2014;Mathers, Hill, Wood, & Wood, 2019;Sarriquet, Bordenave, & Marmonier, 2007). In contrast, in some rivers there may naturally be limited or no vertical hydrological exchange associated with impermeable substrates or reduced connectivity (Malcolm, Soulsby, Youngson, & Petry, 2003).…”

“…Studies that have investigated the behaviour of organisms to environmental cues (e.g. vertical hydrological exchange, streambed drying events) within subsurface sediments have focussed on the vertical distribution of biota by measuring their final position (Foy & Thistle, 1991;Mathers, Hill, Wood, & Wood, 2019;Mathers et al, 2014;Stumpp & Hose, 2013), by using a proxy such as leaf litter breakdown rates (Folegot, Krause, Mons, Hannah, & Datry, 2018), or by assuming use of subsurface sediments when individuals are not observed above surface substrates (Vadher, Stubbington, & Wood, 2015). 5.…”