Animals alter precipitation legacies: Trophic and ecosystem engineering effects on plant community temporal dynamics

Abstract

Multiyear precipitation “legacies” can have stronger effects on plant community composition than rainfall in the current growing season, but variation in the magnitude of these effects is not fully understood. Direct interactions between plants and animals, such as herbivory, and indirect interactions, such as ecosystem engineering (via changes in the physical environment), may influence precipitation legacies by altering mechanisms of lagged effects. However, the role of direct and indirect plant–animal interactions in determining the strength of precipitation legacies remains largely unexplored. Here, we investigated effects of current growing season rainfall and precipitation legacies on grassland composition, and the influence of herbivory and ecosystem engineering interactions on these temporal dynamics. From 2009 to 2014, a period spanning high and low rainfall, we recorded plant cover in kangaroo rat exclosures and paired control plots that included both burrow and inter‐burrow areas. We used linear mixed effects modelling and analysis of community dissimilarities to evaluate plant composition responses to current and previous growing season rainfall and kangaroo rat herbivory (presence of seed foraging) and ecosystem engineering (burrowing). We found that community composition was more strongly affected by precipitation legacies than by current growing season rainfall. Greater precipitation in the previous growing season enhanced grass cover and reduced forb and legume cover. Kangaroo rat trophic and engineering interactions had counteracting effects on these legacies. While burrowing increased grass cover and thereby amplified the effects of previous growing season rainfall on community composition, legacies were suppressed by the presence of kangaroo rat foraging, which decreased grass cover. Further analysis revealed that kangaroo rat foraging and burrowing had conflicting effects on residual plant biomass prior to the growing season, suggesting that precipitation legacies were influenced by altered litter dynamics. Synthesis. Our study demonstrates that animals can impact the strength of precipitation legacies through direct and indirect interactions with the plant species that drive lag effects. The influence of multiple types of plant–animal interactions on precipitation legacies may be important to consider for ecosystem management and when generating predictions of community composition and productivity in future ecosystems.

Herbivory enhances the effect of environmental variability on plant community composition and beta diversity

“…While soil nutrients did matter (there was greater diversity off mound than on in wet years), their spatial variability may be dampened as nutrient availability can be restricted by moisture limitation (Cardinale, Hillebrand, Harpole, Gross, & Ptacnik, 2009). While these results are consistent with a recent study showing that precipitation plays a substantial role in structuring plant communities in Carrizo, lag effects can lead to unexpected patterns via thatch accumulation in subsequent years (Grinath et al, 2018). In this case, grasses can create a positive feedback where, once established, they increase their dominance over time.…”

“…First, like many western grasslands, the Carrizo Plain experiences high precipitation variability, and water is a major limitation to plant productivity. Multiple‐year droughts are interspersed with wet spells, altering both total plant productivity and functional‐group representation (Grinath et al, 2018). Second, the Carrizo Plain is characterized by high spatial resource availability due to the presence of the giant kangaroo rat (GKR; Dipodomys ingens ), an ecosystem engineer that forms evenly spaced mounds over six meters in diameter around its burrows (Grinnell, 1932).…”

Environmental gradients determine the potential for ecosystem engineering effects

“…Bromus madritensis ssp. rubens) are important food sources for the federally endangered giant kangaroo rat (Schiffman 1994, Gurney et al 2015, and kangaroo rat foraging can offset the facilitative effects of burrowing on these grasses (Grinath et al 2018). Indeed, the results presented here indicate that effects of rodent presence on soils and plants are frequently opposite those of rodent burrowing (Fig.…”

“…Hordeum murinum and other exotic grass species can displace native plants at local scales in California grasslands (DiVittorio et al 2007, HilleRisLambers et al 2010, and the facilitative effect of burrowing on such invasions may lead to a decline in landscape-level diversity over time (Schiffman 1994). Burrows are important habitat for native species, such as the forbs Amsinckia tessellata and Caulanthus lasiophyllus (Grinath et al 2018), and their abundances may be particularly prone to decline during rainy periods. These dynamics may be kept in check by climate change, as the region is expected to become more arid in the coming century (Seager et al 2007, Cayan et al 2008.…”

“…Thus, the influence of precipitation on kangaroo rat densitymediated effects on plants were minimal in our experiment. Moreover, burrow position in the landscape is stable through time (Grinath et al 2018) and the kangaroo rats primarily maintain pre-existing burrows over multiple generations (Cooper and Randall 2007), rather than excavating new burrows and changing the amount of burrow structure in the landscape.…”