Abstract
AbstractFoundation species are locally abundant and uniquely control associated biodiversity, whereas dominant species are locally abundant but are thought to be replaceable in ecological systems. It is important to distinguish foundation from dominant species to direct conservation efforts. Long‐term studies that remove abundant species while measuring community dynamics have the potential to (1) aid in the identification of foundation vs. dominant species and, (2) once a foundation species is identified, determine how long its effects persist within a community after its loss. Long‐term data on ant assemblages within two canopy‐manipulation experiments—the Harvard Forest Hemlock Removal Experiment (HF‐HeRE) and the Black Rock Future of Oak Forests Experiment (BRF‐FOFE)—provide insights into how ant assemblages change and reassemble following the loss of Tsuga canadensis or Quercus spp. Previous research documented foundation species effects on ants in the HF‐HeRE for up to four years after T. canadensis loss. Six additional years of data at HF‐HeRE presented for the first time here show that removal of T. canadensis resulted in taxonomic and some measures of functional shifts in ant assemblages that persisted for ten years, further supporting the hypothesis that T. canadensis is a foundation species at Harvard Forest. In contrast, ant assemblages at BRF‐FOFE varied little regardless of whether oaks or other tree species were removed from the canopy, suggesting that Quercus species do not act as foundation species at Black Rock Forest. Deer and moose exclosures within each experiment also allowed for comparisons between effects on ants of foundation or dominant tree species relative to effects of large herbivores. At HF‐HeRE, effects of T. canadensis were stronger than effects of large herbivores on taxonomic and functional diversity of ant assemblages. At BRF‐FOFE, in contrast, effects of Quercus species were weaker than effects of large herbivores on ant taxonomic diversity and some measures of ant functional diversity. These findings illustrate the importance of distinguishing between the roles of irreplaceable foundation species and replaceable dominant ones in forested ecosystems along with other drivers of biodiversity (e.g., herbivory).
Highlights
Ecosystems with high biodiversity are hypothesized to be more resilient to changing environmental conditions than those with lower biodiversity because more species are available in the former to fill functional roles when species are lost
Statistical framework Here, we describe the basic statistical framework for the two experiments, which forms the basis for permutational multivariate analyses of covariance (PERMANCOVAs) of taxonomic diversity and analyses of covariances (ANCOVAs) as implemented with generalized linear mixed models (GLMMs) of univariate taxonomic and functional diversity
Like previous research on ants within Harvard Forest Hemlock Removal Experiment (HF-HeRE) (Sackett et al 2011, Kendrick et al 2015), we found that hemlock control plots were largely dominated by Aphaenogaster picea and Aphaenogaster fulva, but lacked the Formica spp. that eventually colonized et al 2005b), and it is important to distinguish them from replaceable dominant species and from other factors determining ecosystem structure and function (Baiser et al 2013)
Summary
Ecosystems with high biodiversity are hypothesized to be more resilient to changing environmental conditions than those with lower biodiversity because more species are available in the former to fill functional roles when species are lost (i.e., the insurance hypothesis sensu Yachi and Loreau 1999). Foundation species and dominant species tend to be trees and share the following attributes: large size, local abundance, occupying basal positions in local food webs, and controlling ecosystem processes and dynamics principally through nontrophic interactions (Baiser et al 2013). Foundation species differ from dominant species in that the former are thought to be irreplaceable in terms of their control on population and community dynamics and ecosystem processes, whereas the latter are considered replaceable (Ellison et al 2005b). Identifying foundation species should be a key priority for conservation efforts to preserve the processes that they modulate within their communities and ecosystems. In eastern North American forests, Tsuga canadensis (L.) Carriere (eastern hemlock) has been identified as a foundation species (Ellison et al 2005b, 2014); stands dominated by T. canadensis are different, both structurally and functionally, from stands dominated by other conifers or mixtures of various deciduous species. Hemlockdominated stands are dark, cool, and moist; have acidic, nutrient-poor soils with slow rates of nutrient cycling (Orwig et al 2013); and are populated by generally species-poor assemblages of associated plants and animals (Rohr et al 2009, Sackett et al 2011, Orwig et al 2013)
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