A global database and “state of the field” review of research into ecosystem engineering by land animals

Abstract

Ecosystem engineers have been widely studied for terrestrial systems, but global trends in research encompassing the range of taxa and functions have not previously been synthesised. We reviewed contemporary understanding of engineer fauna in terrestrial habitats and assessed the methods used to document patterns and processes, asking: (a) which species act as ecosystem engineers and with whom do they interact? (b) What are the impacts of ecosystem engineers in terrestrial habitats and how are they distributed? (c) What are the primary methods used to examine engineer effects and how have these developed over time? We considered the strengths, weaknesses and gaps in knowledge related to each of these questions and suggested a conceptual framework to delineate "significant impacts" of engineering interactions for all terrestrial animals. We collected peer-reviewed publications examining ecosystem engineer impacts and created a database of engineer species to assess experimental approaches and any additional covariates that influenced the magnitude of engineer impacts. One hundred and twenty-two species from 28 orders were identified as ecosystem engineers, performing five ecological functions. Burrowing mammals were the most researched group (27%). Half of all studies occurred in dry/arid habitats. Mensurative studies comparing sites with and without engineers (80%) were more common than manipulative studies (20%). These provided a broad framework for predicting engineer impacts upon abundance and species diversity. However, the roles of confounding factors, processes driving these patterns and the consequences of experimentally adjusting variables, such as engineer density, have been neglected. True spatial and temporal replication has also been limited, particularly for emerging studies of engineer reintroductions. Climate change and habitat modification will challenge the roles that engineers play in regulating ecosystems, and these will become important avenues for future research. We recommend future studies include simulation of engineer effects and experimental manipulation of engineer densities to determine the potential for ecological cascades through trophic and engineering pathways due to functional decline. We also recommend improving knowledge of long-term engineering effects and replication of engineer reintroductions across landscapes to better understand how large-scale ecological gradients alter the magnitude of engineering impacts.

Restoration potential of threatened ecosystem engineers increases with aridity: broad scale effects on soil nutrients and function

“…Returning locally extinct fauna has recently been recognised as a key component of ecosystem restoration because such species may play trophic or engineering roles important for ecosystem structure (Wilmers and Schmitz 2016, Sobral-Souza et al 2017, Schweiger et al 2018). However, the value of reinstating species for ecosystem function is also likely to be context-dependent (Coggan et al 2016(Coggan et al , 2018.…”

The importance of ecological memory for trophic rewilding as an ecosystem restoration approach

“…This differentiates ecosystem engineers from keystone species, which are defined as species which have a disproportionately large effect on the ecological community relative to their abundance (Paine, 1995) purely by biotic (trophic) interactions, e.g. predation (Coggan, Hayward & Gibb, 2018). These two concepts are particularly relevant in the context of trophic rewilding when (re)introduced species are expected to have a strong impact on the ecosystem (Byers et al, 2006;Svenning et al, 2016).…”

Bioturbation by bandicoots facilitates seedling growth by altering soil properties

“…The loss of these ecosystem engineers may lead to a subsequent loss of the ecological processes they perform and important plant–animal interactions. Globally, conservation efforts include reintroductions of threatened species, increasingly not only for the conservation of species themselves, but also in attempts to restore lost ecosystem functions (e.g., Law, Gaywood, Jones, Ramsay, & Willby, ); and greater understanding on the role of digging mammals in ecosystem function is therefore required (Coggan et al., ). Australia has the world's highest record of mammal extinction in the last 200 years (Woinarski, Burbidge, & Harrison, ), and a large proportion of extant digging marsupials are threatened or have suffered severe range contractions (Fleming et al., ).…”