Publications by Year: 2007

2007
Farrell BD. Insects and Internet: Saving a national treasure in Hispaniola. ReVista : Harvard review of Latin America. 2007;(Fall 2007) :80-81. Full text
Linnen CR, Farrell BD. Mitonuclear discordance is caused by rampant mitochondrial introgression in Neodiprion (hymenoptera : diprionidae) sawflies. Evolution. 2007;61 (6) :1417-1438.Abstract

We investigate the pervasiveness of hybridization and mitochondrial introgression in Neodiprion Rohwer (Hymenoptera; Diprionidae), a Holarctic genus of conifer-feeding sawflies. A phylogenetic analysis of the lecontei species group revealed extensive discordance between a contiguous mitochondrial region spanning three genes (COI, tRNA-leucine, and COII) and three nuclear loci (EF1 alpha, CAD, and an anonymous nuclear locus). Bayesian tests of monophyly and Shimodaira-Hasegawa (SH) tests of topological congruence were consistent with mitochondrial introgression; however, these patterns could also be explained by lineage sorting (i.e., deep coalescence). Therefore, to explicitly test the mitochondrial introgression hypothesis, we used a novel application of coalescent-based isolation with migration (IM) models to measure interspecific gene flow at each locus. In support of our hypothesis, mitochondrial gene flow was consistently higher than nuclear gene flow across 120 pairwise species comparisons (P < 1 x 10(-12)). We combine phylogenetic and coalescent evidence to identify likely cases of recent and ancient introgression in Neodiprion, and based on these observations, we hypothesize that shared hosts and/or pheromones facilitate hybridization, whereas disparate abundances between hybridizing species promote mitochondrial introgression. Our results carry implications for phylogenetic analysis, and we advocate the separation of high and low gene flow regions to inform analyses of hybridization and speciational history, respectively.

Rykken JJ, Moldenke AR, Olson DH. Headwater riparian forest-floor invertebrate communities associated with alternative forest management practices. Ecological Applications. 2007;17 (4) :1168-1183.Abstract

Headwater streams and their riparian zones are a common, yet poorly understood, component of Pacific Northwest, USA, landscapes. We describe the ecological importance of headwater stream riparian zones as habitat for forest-floor invertebrate communities and assess how alternative management strategies for riparian zones may impact these communities. We compared community composition of forest-floor invertebrates at increasing distances along trans-riparian (stream edge to upslope) transects in mature forests, clearcuts, and riparian buffers of similar to 30-m width with upslope clearcuts. Invertebrates were collected using pitfall traps in five replicate blocks of three treatments each in the Willamette National Forest, Oregon, USA. We measured microclimate and microhabitat variables at pitfall locations. Despite strong elevation and block effects on community composition, community analyses revealed a distinct "riparian'' invertebrate community within 1 m of the stream edge in mature forest treatments, which was strongly related to cool, humid microclimate conditions. Invertebrate community composition in buffer treatments was far more similar to that of mature forests than to clearcuts; a pattern mirrored by microclimate. These results suggest that, within our study sites, forest floor invertebrate distributions are strongly associated with microclimate and that riparian buffers of similar to 30-m width do provide habitat for many riparian and forest species. Riparian reserves may serve as effective forest refugia and/or dispersal corridors for invertebrates and other taxa, and their incorporation into watershed management plans likely will contribute to meeting persistence and connectivity objectives.

Rykken JJ, Chan SS, Moldenke AR. Headwater riparian microclimate patterns under alternative forest management treatments. Forest Science. 2007;53 (2) :270-280.Abstract

Management of headwater streams and their riparian zones has included the implementation of forested riparian buffers, which are intended to protect ecological processes (such as microclimate) and biota, but the appropriate widths for these buffers have been widely debated. We measured the magnitude and extent of microclimatic gradients associated with headwater streams in mature unmanaged forests, and determined whether these patterns were maintained in clearcut harvested units with and without a 30 m-wide riparian buffer on each side of the stream. We measured air temperature, soil temperature, and relative humidity between I and 70 m from the stream in five replicate blocks of three treatments each in western Oregon. Results indicated the strongest stream effect on air temperature and relative humidity to be within 10 m of the stream in all management treatments at 3:00 pm, and gradients were evident to 20 m in the forested treatment. The clearcut was significantly hotter (air and soil) and drier than either the riparian buffer or the forest treatments at 3:00 pm. The riparian buffer and forest had similar microclimates at all distances from the stream, suggesting that the 30-m buffer adequately protected the riparian microclimatic gradient. We hypothesize that the strong stream effect on microclimate in the riparian zone serves a critical role in mitigating the influence of microclimatic "edge effects" associated with the forest-clearcut edge. Biota dependent on cool, humid microclimates provided by riparian zones will benefit from the implementation of riparian buffers in harvest units.