Diez et al., 2012

Ecosystems and Extreme Climatic Events (ECEs)

Ecosystems are experiencing not only gradual shifts in mean climate conditions but also dramatic changes in climate variability and the prevalence of extreme climatic events (ECEs). ECEs include events such as droughts, floods, severe storms, and heat waves which are altering in frequency, magnitude, timing, and duration depending on the region and the specific climate event (Easterling et al. 2000; Karl et al. 2008).
The profound impact of these extreme events on terrestrial and aquatic ecosystems has been documented, highlighting that they can synergistically interact with other environmental change factors, such as species invasions, further altering ecosystem dynamics (Parmesan et al. 2000; Thibault and Brown 2008). The interplay between broad climatic shifts and the likelihood of species invasions shows that climatic changes can influence invasion traits with varying effects across different contexts (Rahel and Olden 2008; Walther et al. 2009; Bradley et al. 2010).
Despite the recognition of these changes, the specific role of ECEs in promoting species invasions has not been rigorously evaluated. This guide leverages theory from community ecology and invasion biology to elucidate mechanisms whereby ECEs can affect the establishment and dispersal of introduced species within ecosystems. Furthermore, the guide reviews current empirical evidence depicting ECE impacts on biological invasions and assesses their potential to adjust future species introductions.

Definition of Extreme Climatic Events

ECEs can be defined from two primary perspectives:

  1. Statistical Definition: Extreme climatic events are episodes that fall within the statistical tails of a climate parameter's historical range. A widely used threshold is the most extreme 1% of annual values, denoting an event with a 100-year recurrence interval (e.g., a 80-year flood9 with occurrences once every 100 years). The frequency of these events shifts with changes in mean or variance of climate variables (Meehl et al. 2000).

  2. Organism-Based Criteria: This perspective defines extreme events based on the capacity of specific organisms to acclimate. Gutschick and BassiriRad (2003) suggest that the abruptness of events is integral, as differing physiological tolerances and evolutionary histories impact various organisms.

  3. Integrated Definition: Following Smith (2011), an ECE is defined as an occurrence that leads to statistically rare climatic conditions that alter ecosystem structure and function significantly outside typical variability bounds.

Mechanisms of ECEs Affecting Biological Invasions

Invasion processes encapsulate introducing individuals to a new area, self-sustaining population establishment, and the subsequent spread characterized by growth and ecological impact (Theoharides and Dukes 2007). ECEs can influence the invasion stages through several mechanisms, as outlined below:

  1. Transport Stage: ECEs, such as storms, can facilitate the transport of non-native species' propagules over considerable distances, transcending physical barriers.

  2. Establishment & Spread Stages:

    • Disturbance Events: Extreme events can induce abrupt mortality within resident species, termed “punctuated killing events” (Sousa 1984), which may provide resource opportunities for introduced species (Shea and Chesson 2002). This resource availability is further contingent on the resilience of the native community and the magnitude, duration, frequency, and timing of the events.

    • Stress Events: Events that do not induce mortality but generate stress that limits resident species' resource utilization can also create opportunities for invasive species to establish (abiotic resistance threshold).

Current Knowledge Gaps & Research Priorities

Notably, the current understanding of ECEs' direct effects on species invasions remains limited, with an urgent need to identify critical research areas. This involves:

  • Recognizing species specific traits that favor invasion post-ECEs.

  • Understanding mechanisms affecting native community resilience amid ECEs.

  • Exploring biological thresholds that determine community response to ECEs.

  • Developing experimental and observational studies to ascertain the precise interactions and consequences of ECEs in ecological contexts.

Management Strategies for ECEs and Invasions

Strategies for mitigating the effects of invasions following ECEs should involve:

  • Targeted restoration efforts enhancing community resilience (e.g., rehabilitation of riparian habitats prone to flooding).

  • Monitoring systems to increase awareness of invasive species risks related to ECEs.

  • Developing specific management protocols focused on species likely to invade post-ECEs.

Conclusion

The intersection of ECEs and biological invasions poses significant challenges for ecosystem management and conservation practices. The urgency to comprehend these complexities is essential for effective ecological responses as climate change persists. Future studies should not only evaluate trends in climatic factors but also dissect the mechanisms driving invasion processes across taxa, ecosystems, and biogeographic regions to enable adequate management responses.