Is it common to be rare on the landscape? A test using a novel model system

Abstract

Context Understanding how rare species are distributed can be difficult due to heterogeneity between landscape units. Lack of statistical replication of landscapes can make it difficult to carry out testing. Model systems may be a solution. Objectives We test whether lichen thalli along the trunk of a tree are analogous to habitat patches in a kilometers-extent landscape and hence can function as a model system. This model system allows for increased statistical power. We use this system to test whether landscapes with rare species are different from those without. Methods We sampled macrolichen diversity along the trunk of 24 balsam fir trees in a stand on the Avalon Peninsula, Newfoundland, Canada, along with microclimate variables. We analysed difference in pattern by aspect and along the gradient of 1 m up the trunk as well as between trees containing the rare Erioderma pedicellatum and those without. Results We found no difference in total patch richness or abundance between the micro-landscapes. We found significantly consistent patterns in lichen patches along the trunk. These patterns were similar on the trees with the rare species. Lichen species richness did not differ between trees containing the rare species versus those that did not. Conclusions Lichen patch pattern is statistically similar between trees and as such, these can be considered as replicate landscape units. Thus, landscape ecologists can use micro-landscapes as model systems to conduct observational and manipulative experiments to test questions about spatial pattern and process, such as those concerning distribution of rare species.

A proposed microcosm for landscape ecology – beyond the binary to the patch-mosaic model

“…There have not been many developments of microcosms for landscape ecology experiments, although experimental mesocosms have been proposed as a tool (e.g., Wiens and Milne 1989). Model systems that have been proposed for landscape ecology include soil biocrusts (Bowker et al 2014) and lichen-covered tree trunks (Wiersma and McMullin 2018). Bowker et al (2014) point out that soil biocrusts are most like scaled-down landscapes in that they have similar attributes to kilometers-extent landscapes, such as patch heterogeneity.…”

“…At the same time, they are interesting ecological systems independent of their use as model systems, which is an often-overlooked property of models (Zuk and Travisano 2018). Wiersma and McMullin (2018) proposed a similar system of heterogeneous patches of cryptogams as Bowker et al (2014), but growing along the boles of trees as replicate landscapes. Although Bowker et al’s (2014) system and Wiersma and McMullin’s (2018) share similar types of organisms and patch pattern, Wiersma and McMullin’s (2018) has the additional feature of being explicitly hierarchical (Fig.…”

“…Wiersma and McMullin (2018) proposed a similar system of heterogeneous patches of cryptogams as Bowker et al (2014), but growing along the boles of trees as replicate landscapes. Although Bowker et al’s (2014) system and Wiersma and McMullin’s (2018) share similar types of organisms and patch pattern, Wiersma and McMullin’s (2018) has the additional feature of being explicitly hierarchical (Fig. 1) with the disadvantage relative to Bowker et al’s (2014) of not being transferrable to a lab setting.…”

“…Hierarchy is a key concept in landscape ecology (Urban et al 1987; O’Neill et al 1989; Kotliar and Wiens 1990) and it has been suggested that by harnessing principles of hierarchy and scaling (Urban et al 1987; Urban 2005; Bowker et al 2014), that microlandscape patterns and processes (a level at which experimentation is more feasible) can be extrapolated to larger extents (a level at which many management challenges occur). Wiersma and McMullin (2018) demonstrated that 2 sets of 12 balsam fir ( Abies balsamea ) trees within a very small area (< 100 m apart) share similar patch patterns of macro-lichens along the boles, and proposed that these trees could be considered replicate (micro)landscapes. While this system holds promise as a potential new type of microcosm for landscape ecology, the limited focus of a single species of tree in a restricted geographic area limits the broader applicability of their proposed model system.…”

“…While this system holds promise as a potential new type of microcosm for landscape ecology, the limited focus of a single species of tree in a restricted geographic area limits the broader applicability of their proposed model system. Here, we use additional data – from two species of trees and across a much wider extent (500 km 2 ) and with a broader suite of lichens, to scrutinize Wiersma and McMullin’s (2018) hypothesis that patches of lichens along a tree bole are a model system for landscapes. If the patch-patterns along the boles of trees holds true in this expanded study, then we posit that similar systems in other regions might also function as complex landscape microcosms that could be harnessed for experimentation.…”