Julie K. Combs

Bio: Julie K. Combs is an academic researcher from University of Washington. The author has contributed to research in topics: Pollinator & Seed predation. The author has an hindex of 8, co-authored 9 publications receiving 362 citations.

The Effects of Above- and Belowground Mutualisms on Orchid Speciation and Coexistence

Abstract: Both pollination by animals and mycorrhizal symbioses with fungi are believed to have been important for the diversification of flowering plants. However, the mechanisms by which these above- and belowground mutualisms affect plant speciation and coexistence remain obscure. We provide evidence that shifts in pollination traits are important for both speciation and coexistence in a diverse group of orchids, whereas shifts in fungal partner are important for coexistence but not for speciation. Phylogenetic analyses show that recently diverged orchid species tend either to use different pollinator species or to place pollen on different body parts of the same species, consistent with the role of pollination-mode shifts in speciation. Field experiments provide support for the hypothesis that colonization of new geographical areas requires adaptation to new pollinator species, whereas co-occurring orchid species share pollinator species by placing pollen on different body parts. In contrast to pollinat...

Convergent demographic effects of insect attack on related thistles in coastal vs. continental dunes

Abstract: Insect herbivory is common, but the conditions under which it reduces the fitness and population size of plants remain poorly understood. We quantified population- level impacts of floral herbivory by specialized insects on cobweb thistle ( Cirsium occi- dentale var. occidentale) in a California coastal dune ecosystem, and then compared these demographic effects to those published for Platte thistle ( Cirsium canescens) in similarly designed exclusion experiments in the continental sand dune ecosystem in the Great Plains. As a separate test of the strength of the seed-to-seedling linkage, we quantified seedling establishment rates in seed addition plots and compared these results to those obtained in herbivore exclusion experiments. This is the first test of direct vs. indirect methods of evaluating the potential impact of seed loss in plant dynamics. Floral herbivory on cobweb thistle in coastal dunes substantially reduced key components of plant fitness. Reduction of insect feeding within flower heads with insecticide increased mean per capita seed production by 144-316% and led to a 130-196% increase in cumulative seedling recruit- ment in the next generation, depending on dune habitat. Juvenile plant densities around insecticide-treated plants subsequently increased by .50%. Both seed and flower head addition experiments corroborated the seed limitation of recruitment and juvenile plant establishment for cobweb thistle; exclusion of postdispersal seed predators did not sub- stantially alter this relationship. While seed addition results were qualitatively similar to herbivore exclusion results, seed addition overestimated the seed-seedling transition. These results are broadly parallel to those found previously for Platte thistle in continental dunes, where reduction of insect feeding in Platte thistle flower heads increased mean per capita seed production by 37-240%, depending on year and microhabitat. This reduction in seed translated into a 33-580% increase in cumulative seedling recruitment and juvenile plant density. Thus in both systems, insect exclusions demonstrated that floral herbivory limited numbers of seeds and seedlings and population density of juvenile plants. This unique comparison of effects of insect herbivory on plant dynamics suggests that for related plants, the character and outcome of such interactions are likely to be functionally similar in structurally convergent ecosystems.

A New Model for Training Graduate Students to Conduct Interdisciplinary, Interorganizational, and International Research

Abstract: Environmental challenges are often global in scope and require solutions that integrate knowledge across disciplines, cultures, and organizations. Solutions to these challenges will come from diverse teams and not from individuals or single academic disciplines; therefore, graduate students must be trained to work in these diverse teams. In this article, we review the literature on training graduate students to cross these borders. We then present a National Science Foundation Integrative Graduate Education and Research Traineeship Program at the University of Washington as a model of border-crossing graduate training focused on interdisciplinary, international, and interorganizational (I3) collaborations on environmental challenges. Finally, we offer recommendations from this program to those considering similar I3 training programs, including strategies for maintaining faculty buy-in, for scaffolding student training to cross borders, and for conducting focused group trips that give the students structu...

Invasive competitor and native seed predators contribute to rarity of the narrow endemic Astragalus sinuatus Piper.

Abstract: The conservation of rare plant species hinges on our ability to identify the underlying mechanisms that limit rare plant populations. Theory on rarity suggests that both predispersal seed predation and competition can be important mechanisms influencing abundance and/or distribution of rare plant populations. Yet few studies have tested these interactions, and those that have evaluated each mechanism independently. Astragalus sinuatus Piper (Whited's milkvetch) is a narrow endemic plant species restricted to eight populations within a 10-km2 area in eastern Washington. We used experimental and observational methods to test the effects of native insect predispersal seed predators and an invasive grass (Bromus tectorum L. [cheatgrass]) on seed set and population density of A. sinuatus. We quantified per capita seed production and pod predation rates across four sites and among four years. Seed predation rates were high across four sites (66-82%) and all years (65-82%). Experimental reduction of predispersal seed predators significantly increased per capita seed set of A. sinuatus (164-345%) at two experimental sites. Concurrently, two seed addition experiments demonstrated the effect of seed loss and presence of B. tectorum on seedling recruitment and establishment of A. sinuatus over four growing seasons. In the first seed addition experiment, we found no difference in recruitment and establishment between low (40) and high (120) seed addition levels. In the second addition experiment (one level of addition; 40 seeds), we found that recruitment and survivorship increased 200% in plots where B. tectorum was removed compared to plots where B. tectorum was present. Thus, seed addition had no impact in the presence of B. tectorum; conversely, in the absence of B. tectorum, seed addition was highly effective at increasing population numbers. Results suggest that, in areas where B. tectorum is present, recruitment is site limited, and it is seed limited when B. tectorum is absent. We recommend that managers reduce B. tectorum in an effort to increase population growth of A. sinuatus; in areas where B. tectorum is absent, short-term reduction of insect predators should be considered as a strategy to increase population growth of this rare species.

Traditional Livelihoods, Conservation and Meadow Ecology in Jiuzhaigou National Park, Sichuan, China.

Abstract: Jiuzhaigou National Park (JNP) is a site of global conservation significance. Conservation policies in JNP include the implementation of two national reforestation programs to increase forest cover and the exclusion of local land-use. We use archaeological excavation, ethnographic interviews, remote sensing and vegetation surveys to examine the implications of these policies for non-forest, montane meadows. We find that Amdo Tibetan people cultivated the valley for >2,000 years, creating and maintaining meadows through land clearing, burning and grazing. Meadows served as sites for gathering plants and mushrooms and over 40 % of contemporary species are ethnobotanically useful. Remote sensing analyses indicate a substantial (69.6 %) decline in meadow area between 1974 and 2004. Respondents report a loss of their “true history” and connections to the past associated with loss of meadows. Conservation policies intended to preserve biodiversity are unintentionally contributing to the loss of these ecologically and culturally significant meadow habitats.

Herbivory: effects on plant abundance, distribution and population growth.

Abstract: Plants are attacked by many different consumers. A critical question is how often, and under what conditions, common reductions in growth, fecundity or even survival that occur due to herbivory translate to meaningful impacts on abundance, distribution or dynamics of plant populations. Here, we review population-level studies of the effects of consumers on plant dynamics and evaluate: (i) whether particular consumers have predictably more or less influence on plant abundance, (ii) whether particular plant life-history types are predictably more vulnerable to herbivory at the population level, (iii) whether the strength of plant–consumer interactions shifts predictably across environmental gradients and (iv) the role of consumers in influencing plant distributional limits. Existing studies demonstrate numerous examples of consumers limiting local plant abundance and distribution. We found larger effects of consumers on grassland than woodland forbs, stronger effects of herbivory in areas with high versus low disturbance, but no systematic or unambiguous differences in the impact of consumers based on plant life-history or herbivore feeding mode. However, our ability to evaluate these and other patterns is limited by the small (but growing) number of studies in this area. As an impetus for further study, we review strengths and challenges of population-level studies, such as interpreting net impacts of consumers in the presence of density dependence and seed bank dynamics.

Ecological and Evolutionary Consequences of Multispecies Plant-Animal Interactions

Abstract: ▪ Abstract Ecologists and evolutionary biologists are broadly interested in how the interactions among organisms influence their abundance, distribution, phenotypes, and genotypic composition. Recently, we have seen a growing appreciation of how multispecies interactions can act synergistically or antagonistically to alter the ecological and evolutionary outcomes of interactions in ways that differ fundamentally from outcomes predicted by pairwise interactions. Here, we review the evidence for criteria identified to detect community-based, diffuse coevolution. These criteria include (a) the presence of genetic correlations between traits involved in multiple interactions, (b) interactions with one species that alter the likelihood or intensity of interactions with other species, and (c) nonadditive combined effects of multiple interactors. In addition, we review the evidence that multispecies interactions have demographic consequences for populations, as well as evolutionary consequences. Finally, we expl...

The ecological and evolutionary implications of merging different types of networks

Abstract: Interactions among species drive the ecological and evolutionary processes in ecological communities. These interactions are effectively key components of biodiversity. Studies that use a network approach to study the structure and dynamics of communities of interacting species have revealed many patterns and associated processes. Historically these studies were restricted to trophic interactions, although network approaches are now used to study a wide range of interactions, including for example the reproductive mutualisms. However, each interaction type remains studied largely in isolation from others. Merging the various interaction types within a single integrative framework is necessary if we want to further our understanding of the ecological and evolutionary dynamics of communities. Dividing the networks up is a methodological convenience as in the field the networks occur together in space and time and will be linked by shared species. Herein, we outline a conceptual framework for studying networks composed of more than one type of interaction, highlighting key questions and research areas that would benefit from their study.

Orchid phylogenomics and multiple drivers of their extraordinary diversification.

Abstract: Orchids are the most diverse family of angiosperms, with over 25 000 species, more than mammals, birds and reptiles combined. Tests of hypotheses to account for such diversity have been stymied by ...

Phylogenetic evidence for pollinator-driven diversification of angiosperms.

Abstract: Since Darwin, the diversity of flowers has been attributed to selection by pollinators. Although pollinators commonly act as selective agents on floral traits, determining the extent to which they have influenced angiosperm diversification requires a historical perspective. Here we review recent studies that combine species-level phylogenies with pollinator data and show that pollinator shifts are common, being associated with at least a quarter of documented divergence events. However, shift frequency and directionality vary extensively, owing to variation in intrinsic factors such as floral features and phylogenetic history, as well as extrinsic factors such as interactions with local pollinator assemblages. Despite technical advances, phylogenies remain limited in their power to distinguish among various pollinator-driven evolutionary processes.