Ashley Asmus

Higher predation risk for insect prey at low latitudes and elevations

Risky in the tropics It is well known that diversity increases toward the tropics. Whether this increase translates into differences in interaction rates among species, however, remains unclear. To simplify the problem, Roslin et al. tested for predation rates by using a single approach involving model caterpillars across six continents. Predator attack rates were higher toward the equator, but only for arthropod predators. Science, this issue p. 742 Like diversity, predation rates among insects increase toward the equator and at lower altitudes. Biotic interactions underlie ecosystem structure and function, but predicting interaction outcomes is difficult. We tested the hypothesis that biotic interaction strength increases toward the equator, using a global experiment with model caterpillars to measure predation risk. Across an 11,660-kilometer latitudinal gradient spanning six continents, we found increasing predation toward the equator, with a parallel pattern of increasing predation toward lower elevations. Patterns across both latitude and elevation were driven by arthropod predators, with no systematic trend in attack rates by birds or mammals. These matching gradients at global and regional scales suggest consistent drivers of biotic interaction strength, a finding that needs to be integrated into general theories of herbivory, community organization, and life-history evolution.

NDVI as a predictor of canopy arthropod biomass in the Alaskan arctic tundra

The physical and biological responses to rapid arctic warming are proving acute, and as such, there is a need to monitor, understand, and predict ecological responses over large spatial and temporal scales. The use of the normalized difference vegetation index (NDVI) acquired from airborne and satellite sensors addresses this need, as it is widely used as a tool for detecting and quantifying spatial and temporal dynamics of tundra vegetation cover, productivity, and phenology. Such extensive use of the NDVI to quantify vegetation characteristics suggests that it may be similarly applied to characterizing primary and secondary consumer communities. Here, we develop empirical models to predict canopy arthropod biomass with canopy-level measurements of the NDVI both across and within distinct tundra vegetation communities over four growing seasons in the Arctic Foothills region of the Brooks Range, Alaska, USA. When canopy arthropod biomass is predicted with the NDVI across all four growing seasons, our overall model that includes all four vegetation communities explains 63% of the variance in canopy arthropod biomass, whereas our models specific to each of the four vegetation communities explain 74% (moist tussock tundra), 82% (erect shrub tundra), 84% (riparian shrub tundra), and 87% (dwarf shrub tundra) of the observed variation in canopy arthropod biomass. Our field-based study suggests that measurements of the NDVI made from air- and spaceborne sensors may be able to quantify spatial and temporal variation in canopy arthropod biomass at landscape to regional scales.

Nestling growth rates in relation to food abundance and weather in the Arctic

ABSTRACT Raising nestlings to fledging is energetically demanding for songbirds, requiring parents to balance several major tradeoffs. Nestling growth rates are highly susceptible to variation in environmental conditions and parental investment, and highly variable environments with short breeding seasons such as the Arctic magnify these tradeoffs. Arctic-nesting passerines provide a good model system in which to explore variation within and between species in growth rates with regard to environmental conditions and the timing of clutch initiation. Here we investigated interannual and interspecies variation in nestling mass gain for 2 species of Arctic-breeding passerine, Gambels White-crowned Sparrow (Zonotrichia leucophrys gambelii) and Lapland Longspur (Calcarius lapponicus), across 2 years. The nestling period of 2014 was both colder (with lower minimum and maximum temperatures) and wetter (with 73% more rainfall) than 2013. Arthropod biomass was also reduced in shrub tundra in 2014 compared to 2013. Both species showed reductions in rate of daily mass gain of nestlings in 2014 compared to 2013, but we observed no significant difference between species. Furthermore, we found that in 2014 early nesting birds had higher rates of nestling growth than those initiating clutches later in the season. These findings suggest that overall environmental conditions were more challenging for raising nestlings in 2014 compared to 2013 and that these differences were manifested in a reduced rate of nestling mass gain in both species. Furthermore, both species showed a negative correlation between precipitation and growth rates, whereas only Lapland Longspur showed a positive correlation between growth rates and temperature.

QTLs for biomass and developmental traits in switchgrass (Panicum virgatum).

Genetic and genomic resources have recently been developed for the bioenergy crop switchgrass (Panicum virgatum). Despite these advances, little research has been focused on identifying genetic loci involved in natural variation of important bioenergy traits, including biomass. Quantitative trait locus (QTL) mapping is typically used to discover loci that contribute to trait variation. Once identified, QTLs can be used to improve agronomically important traits through marker-assisted selection. In this study, we conducted QTL mapping in Austin, TX, USA, with a full-sib mapping population derived from a cross between tetraploid clones of two major switchgrass cultivars (Alamo-A4 and Kanlow-K5). We observed significant among-genotype variation for the vast majority of growth, morphological, and phenological traits measured on the mapping population. Overall, we discovered 27 significant QTLs across 23 traits. QTLs for biomass production colocalized on linkage group 9b across years, as well as with a major biomass QTL discovered in another recent switchgrass QTL study. The experiment was conducted under a rainout shelter, which allowed us to examine the effects of differential irrigation on trait values. We found very minimal effects of the reduced watering treatment on traits, with no significant effect on biomass production. Overall, the results of our study set the stage for future crop improvement through marker-assisted selection breeding.

The detritus-based microbial-invertebrate food web contributes disproportionately to carbon and nitrogen cycling in the Arctic

The Arctic is the world’s largest reservoir of soil organic carbon and understanding biogeochemical cycling in this region is critical due to the potential feedbacks on climate. However, our knowledge of carbon (C) and nitrogen (N) cycling in the Arctic is incomplete, as studies have focused on plants, detritus, and microbes but largely ignored their consumers. Here we construct a comprehensive Arctic food web based on functional groups of microbes (e.g., bacteria and fungi), protozoa, and invertebrates (community hereafter referred to as the invertebrate food web) residing in the soil, on the soil surface and within the plant canopy from an area of moist acidic tundra in northern Alaska. We used an energetic food web modeling framework to estimate C flow through the food web and group-specific rates of C and N cycling. We found that 99.6% of C processed by the invertebrate food web is derived from detrital resources (aka ‘brown’ energy channel), while 0.06% comes from the consumption of live plants (aka ‘green’ energy channel). This pattern is primarily driven by fungi, fungivorous invertebrates, and their predators within the soil and surface-dwelling communities (aka the fungal energy channel). Similarly, >99% of direct invertebrate contributions to C and N cycling originate from soil- and surface-dwelling microbes and their immediate consumers. Our findings demonstrate that invertebrates from within the fungal energy channel are major drivers of C and N cycling and that changes to their structure and composition are likely to impact nutrient dynamics within tundra ecosystems.

Publisher Correction to: Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome

The above mentioned article was originally scheduled for publication in the special issue on Ecology of Tundra Arthropods with guest editors Toke T. Høye . Lauren E. Culler. Erroneously, the article was published in Polar Biology, Volume 40, Issue 11, November, 2017. The publisher sincerely apologizes to the guest editors and the authors for the inconvenience caused.

Shrub shading moderates the effects of weather on arthropod activity in arctic tundra: Shrub cover affects arctic arthropod activity

1. Rapid warming has facilitated an increase in deciduous shrub cover in arctic tundra. Because shrubs create a cooler microclimate during the growing season, shrub cover could modulate the effects of global warming on the phenology and activity of ectotherms, including arthropods. This possibility was explored here using two dominant arthropod groups (flies and wolf spiders) in Alaskan tundra.

Tundra-Taiga Biology: Human, Plant, And Animal Survival In The Arctic. By R. M. M. Crawford: New York: Oxford University Press, 2014. 270 pp.

Professor Emeritus R. M. M. Crawford has written an engaging, thorough, and current text describing the arctic biome and its inhabitants. The unifying theme, as laid out in the preface, is considering how resident arctic organisms are able to survive the long, harsh winter period. An evolutionary perspective is woven throughout the book, reminding readers of the history of this part of the Earth and the adaptations the flora and fauna must have to persist in the Far North. Generally, the book seems to be written for the lay person who has an interest in natural history, but with occasional indepth, technical descriptions of a particular biological process or pattern. Thus, the text is appropriate for an upper-level undergraduate or graduate level course. In addition, this book would be an excellent introduction to the tundra and boreal forest for anyone traveling to the region to conduct research or with a strong interest in biology. The text is accessible, well written, and easy to understand. Crawford enhances particular case studies and descriptions with terms like “surprising” and “counter-intuitive” so that his own voice rings through. Other colorful phrases like “marauding botanists” enliven the text along with occasional personal anecdotes. He often places biological discoveries in their historical context, such that scientific inquiry and debate are central to the narrative. By elaborating uncertainties and knowledge gaps where they exist, he inspires the reader’s own curiosity. Case studies of unusual adaptations are intriguing, and Crawford’s interest in them engages the reader. The transitions between chapters emphasize the themes of the book, and guide the reader along well. In particular, intraand inter-annual variations in abiotic conditions are touched on repeatedly so that the evolutionary context for the adaptations is well described. The individual chapters can stand on their own, which leads to some repetition among them. For an instructor using this text this would be an advantage, as individual chapters could be assigned to students to focus on particular topics. The history described in the first three chapters would help students understand how current environmental changes fit in the context from the past. For example, Chapter 1 presents the history of the arctic climate and could be an excellent supplement to a course on climate change that includes the Arctic as a region undergoing dramatic change. Chapter 2 describes the paleo-arctic environment, setting up the themes of inter-annual variation and biological adaptations. Students studying the tundra and taiga today would greatly benefit from this historical perspective. Not surprisingly, given Crawford’s expertise, Chapter 9 on evolution is excellent. For readers relatively unfamiliar with the Arctic, Crawford’s recurrent theme of adaptations will be illuminating. In addition to the adaptations of year-round residents, the migration of other animals is explored relative to its biological costs and benefits. In this vein, the discussion regarding how plants need to be able to not grow in the Arctic to avoid damaging weather conditions provides a memorable topic. Phrasing like this is colorful and helpful in reinforcing the unique environment of the tundra and taiga. Some readers might find it surprising that Crawford allocates a significant amount of text to the discussion of human inhabitants and explorers of the Arctic. In addition to a section devoted to human biogeography and survival (Chapter 3), the evolution of humans (Chapter 9) and the effects of pollution (Chapter 10) in the Arctic are discussed at length. Here, too, Crawford emphasizes the theme of adaptation and resilience in an adverse environment. A tasteful balance of history, science, and anecdote in these sections frames the central issue: conserving and living in the Arctic in a changing world. Importantly for use as a text, recent literature and key upto-date references are cited throughout the book. For example, Chapter 4 discussing tundra diversity incorporates current understanding of climate change. Predator-prey interactions (Chapter 8) highlight recent studies suggesting that predation may be quite important in arctic ecosystems because of limited food web length. However, a handful of topics in the text were not as well supported by the ecological literature. For example, in Chapter 8, Crawford suggests that mammals are required for nutrient cycling in the tundra. Although several studies confirm that nutrient cycling can be significantly affected by intense mammalian grazing (e.g., Väisänen et al. 2014), grazing intensity varies substantially across the landscape both temporally and spatially; thus, such generalizations are not well substantiated. Occasionally some organisms seemed to be missing from certain chapters. For example, there was no mention of insects or migratory songbirds in the first discussion of diversity in Chapter 4. But these are relatively minor issues, as the text as a whole is well supported and an excellent description of this region. The figures in general are terrific, with high-quality photographs and a great use of color. The inclusion of many maps is helpful to the reader unfamiliar with this region. More complex scientific figures, many taken from recent primary literature, enhance the utility of the book as a learning tool for biology students and researchers. These are complemented by a glossary and an excellent list of references, which would also be helpful to instructors wishing to design a course or discussion centered on a topic in the book. In terms of presentation, a future edition of the book would benefit from some minor editorial corrections. Occasionally, the maps need better placement as they were out of context, and in some cases the figures are not cited in order, making reference a bit challenging. There are a few typographic errors. Finally, the last chapter looks forward and considers how tundra and taiga may respond to current and predicted environmental changes. The theme here is resilience, emphasizing the past changes that these organisms and communities have withstood. These are topics covered by other authors as well, but Crawford develops a convincing argument for resilience based on the background reviewed in the previous chapters. This is an excellent book.