Resilience of Novel Ecosystem Under Global Change — Series2
By: Akika Takada
Tags: Global Change, Resilience, Ecology, Novel Ecosystem

Introduction

Global ecosystems have been dramatically reshaped by human activities (Vitousek, Mooney, Lubchenco & Melillo, 1997). The major drivers that affect ecosystems including land use change, climate change, nitrogen deposition, biotic exchange and increasing atmospheric carbon dioxide (Sala et al., 2000). Although their impacts are context dependent, these impacts all share a common trait, which is bringing novelty to the specific contexts (Kueffer, 2015). Emerging novelty in ecosystems has resulted in the concept of novel ecosystems, which is defined by the unorthodox combination of biotic and abiotic conditions under the human-caused change of disturbance regime (Hobbs et al., 2006). Further changes in ecosystem structure and function lead to the potential shift to irreversible alternative states (Barnosky et al., 2012; Scheffer, Carpenter, Foley, Folke & Walker, 2001). The lack of understanding of the ecosystem dynamic makes traditional management approaches impractical and inefficient (Seastedt, Hobbs & Suding, 2008). Under global change, ecosystem management needs to aim for maintaining ecosystem resilience, which is the capacity of absorbing disturbances and maintain its structure and function (Crépin, Biggs, Polasky, Troell & de Zeeuw, 2012; Holling, 2001; Seidl, Spies, Peterson, Stephens & Hicke, 2016). The application of the concept of ecological resilience to maintain a healthy and functional ecosystem is proliferating in this decade, however, the novelty from rapid global change indicates the importance of rethinking the conventional approach used for ecosystem management (Côté & Darling, 2010; Hobbs, Higgs & Harris, 2009; Hobbs et al., 2014; Meijaard, Albar, Rayadin, Ancrenaz & Spehar, 2010; Mumby, Chollett, Bozec & Wolff, 2014; Sasaki, Furukawa, Iwasaki, Seto & Mori, 2015). Therefore, there is an urgent need for understanding ecological resilience in novel ecosystems under global change.

What is Resilience?

Understanding the dynamic nature of ecosystems has been a key goal of ecologists for decades. In the early development of the theory of resilience, stability was focused on as a mechanism that maintains the equilibrium state of an ecosystem, which means that an ecosystem will always recover to a persistent state in form and function (Lewontin, 1969). In other words, it is called engineering resilience (Holling, 1978), where only one equilibrium steady state is allowed to exists. However, the equilibrium state is less meaningful when considering the probability of extinction of the species due to continuous and unexpected disturbances that drive the ecosystem dynamic. The conditions that support the recovery under a wide range of variables and promotes persistence of relationships in a domain of attraction, where stability occurs is, instead, of interest. This is where the concept of ecological resilience comes in. Ecological resilience is defined as the capacity of a system to absorb disturbance and still retain its basic function and structure (Holling, 1973). It recognises the dynamic nature that discontinuous and non-linear ecological change could shift the system into an alternate regime of stability domain (Scheffer, Carpenter, Foley, Folke & Walker, 2001). Stability domain is a basin of attraction of a system where its dimensions are determined by thresholds level of controlling variables (Folke et al., 2010). Therefore, resilience is defined by how an ecosystem responds to the key processes that change ecosystem function and structure.

Ecological change in ecosystem function and structure is driven by the cross-scale interaction of internal and external components, which is biodiversity and disturbance, that both stabilise and destabilise the system (Holling, 1986). As a slow-changing variable that is thought to be significant to determine the boundary of a state, biodiversity plays a key role in renewal and reorganisation of ecosystems after disturbance and provides insurance for sustaining current desired states of dynamic ecosystem regimes (Folke et al., 2004); As a major natural process that affecting the ecosystem, disturbances moderate temporal and spatial heterogeneity in the natural community (Connell, 1978; Pickett, Kolasa, Armesto & Collins, 1989; White & Pickett, 1985). Biodiversity and disturbance interact within or across scales to form a complex and functional network that maintains ecosystem function and structure and further generates ecological resilience. Recently, the topic of ecological resilience has become one of great concern since humans have dramatically modified ecosystems by changing biodiversity and disturbance regimes in. These changes have led to regime shifts where the ecosystem lost its function for providing crucial ecosystem services (Scheffer et al., 2001). It also resulted in the creation of novel ecosystems where humans play a key role in ecosystem development and the changes to ecosystem properties (Morse et al., 2014).