Ermias T. Azeria

Effects of habitat characteristics and interspecific interactions on co-occurrence patterns of saproxylic beetles breeding in tree boles after forest fire: null model analyses

It is often suggested that habitat attributes and interspecific interactions can cause non-random species co-occurrence patterns, but quantifying their contributions can be difficult. Null models that systematically exclude and include habitat effects can give information on the contribution of these factors to community assembly. In the boreal forest, saproxylic beetles are known to be attracted to recently burned forests where they breed in dead and dying trees. We examined whether species co-occurrences of saproxylic beetles that develop in, and emerge from, boles of recently burned trees show non-random patterns. We also estimated the extent to which both the post-fire habitat attributes and interspecific interactions among beetles contribute to such patterns. We sampled tree boles encompassing key attributes (tree species, tree size/dbh and burn severity) that are thought to characterize species–habitat associations of saproxylic beetles, a proposition that we tested using indicator species analysis. Two null models with no habitat constraints (“unconstrained”) indicated that a total of 29.4% of the species pairs tested had significant co-occurrence patterns. Habitat-constrained null models indicated that most of the detected species aggregations (72%) and segregations (59%) can be explained by shared and distinct species–habitat relationships, respectively. The assembly pattern was also driven by interspecific interactions, of which some were modulated by habitat; for example, predator and prey species tended to co-occur in large-sized trees (a proxy of available bark/wood food resource primarily for the prey). In addition, some species segregation suggesting antagonistic, competitive, or prey–predator interactions were evident after accounting for the species’ affinities for the same tree species. Overall, our results suggest that an intimate link between habitat and interspecific interactions can have important roles for community assembly of saproxylic assemblages even following disturbance by fire. We also show that a systematic application of null models can offer insight into the mechanisms behind the assembly of ecological communities.

Saproxylic Beetles in Disturbed Boreal Forests: Temporal Dynamics, Habitat Associations, and Community Structure

Abstract: Early postfire habitats harbour numerous saproxylic species. Some are opportunistic feeders, while others are closely associated with burned forests. This distinction is important for developing sound postfire forest management aimed at conserving biodiversity, as concerns should be mostly directed towards burn-associated saproxylic beetles rather than opportunistic species. Here, we examine species-habitat associations, temporal dynamics, and community structure of saproxylic beetles in black spruce and jack pine stands disturbed by wildfire and by a “non-fire” disturbance generated by girdling trees to mimic the small-scale gap dynamics characterizing old-growth boreal forests in Canada. We used flightinterception traps and reared logs to compare abundance, species richness, and species composition of saproxylic beetles among treatments. We found that over 30% of saproxylic beetles had an affinity with jack pine or black spruce affected by either fire or girdling. Assemblages consistently differed between disturbance types over the 3 y of the study. We found that successional changes in species composition were more pronounced in burned sites than those with the girdling treatment, which indicates that the contribution of fire-generated habitats to regional diversity increases over time. While postfire forests are notable for their early-colonizing saproxylic species, our results show that they can also have substantial value for supporting mid-successional species such as Acmaeops pratensis, which is already on European red lists. This forewarns us about long-term negative consequences that postfire salvage logging could have for certain species.

Landscape-scale disturbances modified bird community dynamics in successional forest environment.

Ecosystem-based forest management strives to develop silvicultural practices that best emulate natural disturbances such as wildfire to conserve biodiversity representative of natural forest ecosystems. Yet, current logging practices alter forest structure and reduce the proportion of old-growth forest and, consequently, can exert long-term effects on the dynamics of forest biota. The stand- and landscape-scale factors driving bird community dynamics in post-disturbance environment remain poorly understood. In this study, we examined bird community dynamics along successional gradients in boreal ecosystems originating from fire and logging in landscapes dominated by old-growth forest. We tested if bird species richness and community compositions in clear-cutting stands became comparable to those in natural stands after 70 years, and identified the relative contributions of stand- and landscape-scale forest attributes in bird community dynamics. Based on records of bird occurrences at 185 field sites in natural and clearcutting stands, we demonstrate that (1) both forest structures and bird communities underwent evident changes along successional gradients in post-clearcutting environment; (2) bird species richness and community composition in 60- to 70-years-old clearcutting stands still differed from those in 50- to 79-years-old natural stands, in spite of the fact that most forest attributes of clearcutting stands became comparable to those of natural stands after 40 years; and (3) landscape disturbances contributed more than stand characteristics in explaining the lack of convergence of mature forest species, residents, and short-distance migrants in post-clearcutting environment. Our study points out that more regards should be paid to improve the landscape configuration of the managed forests, and implies that old-growth forest retention within logged areas, combined with selection cutting and prolonged logging rotations, can better emulate fire and alleviate forest harvesting effects on bird community assemblages typical of natural boreal ecosystem.

Differential Effects of Post-Fire Habitat Legacies on Beta Diversity Patterns of Saproxylic Beetles in the Boreal Forest

Abstract: Fire-generated mosaics of habitat legacies such as dead and dying trees are key structural components in boreal forest ecosystems that support diverse saproxylic beetles. Our study sought to elucidate the spatial pattern of community composition (beta diversity) of saproxylic beetles along gradients of post-fire habitat legacies (tree species composition, tree size [dbh], and burn severities) and geographical distance. For 2 y, we reared saproxylic beetles from 360 logs retrieved from 72 sites in burned forests. Tests were performed to explain the overall beta diversity (&bgr;sor) by partitioning it into its 2 components: the “species spatial turnover” due to species replacement (&bgr;sim) and the “richness-driven” beta diversity due to species richness differences (&bgr;rich)- Variations in tree species, tree size, and burn severity had significant effects on overall beta diversity (&bgr;sor) of saproxylic beetles; these effects varied according to the differential influence of these factors on the 2 distinct components of beta diversity. Tree composition had notable effects on species spatial turnover (&bgr;sim), for which saproxylic species composition differed between jack pine and black spruce, and it was more variable between jack pine sites than between black spruce sites. On the other hand, variation in tree size was primarily responsible for the richness-driven beta diversity component (&bgr;rich), which was highest between the smallest and largest dbh groups and lowest between largest and mid-sized trees. Similarly, richness-driven composition differed significantly across severity gradients and was highest across low to high severity and lowest between low-severity stands. Broader geographical distance per se did not affect compositional patterns of saproxylic beetles, yet the landscape context could have some effect. These results could have crucial implications for post-fire management, which also aims to efficiently conserve saproxylic beetles. The significant spatial turnover in saproxylic composition between black spruce and jack pine and the underlying host-tree specificity suggest that a mosaic of both tree species should be maintained in the landscape. The richness-driven beta diversity pattern along the tree size and severity gradients implies that it may be necessary to prioritize the most species-rich classes, such as larger trees with lower severity burns, but with qualifications to cater also for species displaying idiosyncratic distributions.

Towards a Better Understanding of Beta Diversity: Deconstructing Composition Patterns of Saproxylic Beetles Breeding in Recently Burnt Boreal Forest

Biodiversity patterns vary across space and time, and this variation is thought to be driven by several ecological/biogeographical processes that act upon species distributions and leave their imprint at various spatial and temporal scales (Huston, 1994; Ricklefs, 2004). The regional or geographical (gamma diversity) diversity patterns, in addition to local diversity (alpha diversity), are consequent upon the extent of “spatial” variation in species composition among sites (beta diversity) (Whittaker, 1960; 1972). Arrays of ecological hypotheses have been proposed as determinants of beta diversity patterns. It can arise from variation in environmental/habitat heterogeneity among sites, spatial constraints, disturbance regimes, and corresponding species-level variations in life history traits (e.g., dispersal, niche-breadth) (Harrison et al., 1992; Nekola & White, 1999; Chase, 2007; Veech & Crist, 2007; Baselga, 2008) as well as neutral and/or stochastic processes (Hubbell, 2001; Chase, 2010). Nevertheless, beta diversity patterns and the mechanisms by which ensembles of local communities maintain their variations and, consequently, influence diversity at regional scale remains a central challenge in ecological and conservation studies (Wilson & Shmida, 1984; Veech & Crist, 2007; Baselga, 2010; Chase, 2010; Tuomisto, 2010; Anderson et al., 2011). Despite its apparent conceptual simplicity, the empirical assessment of beta diversity has been mired with extensive debates over a perplexing array of indices, analytical approaches, or scales of analysis (Wilson & Shmida, 1984; Lande, 1996; Loreau, 2000; Koleff et al., 2003; Tuomisto & Ruokolainen, 2006; Legendre et al., 2008; Veech & Crist, 2010; for a detailed outline of the issues, see recent review by Anderson et al., 2011). One of the most fundamental and recurrent challenges in beta diversity studies has been distinguishing and quantifying the pure “spatial” turnover component of beta diversity from that caused by variation in species richness between local communities (Wilson & Shmida, 1984; Koleff et al., 2003; Veech & Crist,

Tackling rarity and sample bias with large-scale biodiversity monitoring: a case study examining the status, distribution and ecology of the lichen Cladonia rei in Alberta, Canada

Species conservation depends on accurate data, but for many lichens existing collections are geographically biased and contain many taxonomic errors. It is unclear whether ‘non-expert’, systematic monitoring schemes can address these sources of error, particularly for taxonomically challenging lichens (e.g. species requiring chemistry for accurate identification). In this case study we use the Alberta Biodiversity Monitoring Institute (ABMI), a large-scale, systematic, multi-taxon monitoring programme, to better understand the ecology and distribution of a putative rare species, Cladonia rei. Collections of C. rei from Alberta dating from 1947 suggested the species was broadly distributed but rare, with seven accessioned specimens.We used comparative morphology, thin-layer chromatography and habitat modelling to compare historical records against more recent material from ABMI surveys. Contrary to the historical collections, ABMI samples suggest C. rei is almost entirely limited to the dry mixed grassland, northern fescue grassland and aspen parkland natural regions, and that within these ecosystems it is relatively common. The typical ecotype exhibited included a persistent primary thallus, podetia with a persistent basal cortex, and secondary squamules; typically they lacked cups, well-developed apothecia and fumarprotocetraric acid, and ramifications were sparse. Cladonia rei was consistently found in pastures and undisturbed grasslands that hosted relatively rich communities of epigeic lichens, thus it does not appear to act as a pioneer inAlberta or to commonly occupy the anthropogenic niches documented elsewhere. In summary, large-scale, systematic, non-targeted monitoring employing novices redressed issues of sample bias through almost 300 C. rei collections, simultaneously improving the ecological understanding of a putative rare species.