Spatiotemporal variation in drivers of parasitoid metacommunity structure in continuous forest landscapes

Abstract

Although landscape spatial structure is known to influence spatial patterns of biodiversity, its effect on insect communities at higher trophic levels such as parasitoids remains poorly understood. This is particularly true in continuously distributed forests in which it can be difficult to identify clear boundaries among habitat patches. Using the metacommunity framework, we evaluate the relative importance of forest landscape structure, non‐environmental spatial structure, and host outbreak status to spatial and within‐season temporal variation in parasitoid communities. We used variation partitioning and metacommunity structure analyses to identify (1) the drivers of the metacommunity structure of parasitoids associated with the spruce budworm (Choristoneura fumiferana), and (2) how their relative influence varies through a season. We used a multi‐scale perspective to summarize landscape heterogeneity in regions of increasing size around the community sampling locations. Spruce budworm larvae and pupae were sampled during three periods during the summer 2014 in 18 locations within continuous forest landscapes in Quebec, Canada. Thirty‐two parasitoid wasp and fly species were recorded, 16 of which were found at more than one location. We found that the mechanisms shaping metacommunity structure changed over the course of a single season and that community structure varied among sites. At early and late periods in the season, we found that non‐environmental structure, forest structure, and likely inter‐specific competition were the main mechanisms influencing spatial variation in community structure. These results suggest a competition–dispersal trade‐off. In contrast, at the middle period of the season, environmental filtering by forest structure and stochastic events were found to influence community structure. This period corresponds to the transition between early and late parasitoid communities. Our findings on the role of environmental filtering and forest structure support the idea that forest manipulations have the potential to influence parasitoid populations and hence spruce budworm outbreak dynamics as hypothesized by the “enemies hypothesis.” Moreover, our study highlights the value of considering a multi‐scale approach and temporal variability of species interactions when characterizing the multiple processes shaping spatial metacommunity structure, particularly in continuous environments.

A Conceptual Framework for the Spruce Budworm Early Intervention Strategy: Can Outbreaks be Stopped?

“…Recent work by Régnière et al [28] suggests that this threshold for spruce budworm in relatively pure balsam fir stands lies around four fourth-instar feeding larvae per 45 cm branch tip, which roughly translates to seven second-instar larvae (L2) per branch. This is likely conservative, as stands with higher hardwood content would have a higher density threshold owing to population dilution and more diverse and robust natural enemy communities [33][34][35][36]. Thus, the aim (and challenge) of EIS is to detect local populations as they surpass the irruption threshold (i.e., become hotspots) and cause sufficient mortality to return them to the lower equilibrium state ( Figure 2).…”

“…A third registered product, a synthesized spruce budworm pheromone, could disrupt Several studies also suggest that during spruce budworm outbreaks, stand-level and landscape-level defoliation and growth loss in balsam fir may decline with increasing proportions of non-host, hardwood species [46][47][48]. Reduced population growth rates and associated outbreak severity in mixed or hardwood-dominated areas ( Figure 3) may reflect increased parasitoid community complexity and pressure [33][34][35][36] or increased dispersal mortality during early instars. Zhang et al [48] also showed, however, that hardwood effects are most evident during the rising phase of an outbreak and become muted as overall defoliation severity increases.…”

Metacommunity theory for transmission of heritable symbionts within insect communities

“…However, spatial frameworks similar to metacommunities (e.g., metapopulation and epidemiological models; Keeling, Bjørnstad, & Grenfell, 2004, and island biogeography; Reperant, 2009) have been successfully applied to systems with mobile hosts. Similarly, the metacommunity framework has been applied to systems without clearly definable patches (Marrec, Pontbriand-Paré, Legault, & James, 2018). Therefore, it is still possible to match spatial assumptions under these circumstances.…”

Hymenoptera functional groups’ shifts in disturbance gradients at Andean forests in Southern Ecuador

“…No differences among conservation levels were found. Restoration may favour the presence of wild bees (Araújo et al 2018;Taki et al 2018;Alvarenga et al 2020) and parasitoids (Marrec et al 2018), but some hymenopteran assemblages from restored areas may be functionally similar to those from forests (Montoya-Pfeiffer et al 2020), and their diversity has been found to be lower in forests compared to more open areas (Pardo and Gonzalez 2007). Therefore, it seems that, even when the areas labeled as low conservation presented a high degree of perturbation, being embedded into a preserved area matrix helped to increase diversity in these areas, since the hymenopteran diversity is positively affected by the proximity to forest (Banks et al 2013).…”

“…Since hymenopteran families may have different responses to habitat degradation (Banks et al 2013), they may also have different responses when being monitored in ecological restoration projects, as well as the roles they play in the ecosystem. For instance, bee and parasitoid diversity has been shown to be higher in restored areas than in disturbed ones (Barbieri Junior and Penteado-Dias 2012; Marrec et al 2018) but the species interaction and functions appear to take a longer time to recover (Albrecht et al 2007). Therefore, species diversity per se may not be the best predictor of ecosystem services, but, rather, diversity at the functional level (Griffin et al 2013).…”