Lacy D. Chick

Upward ant distribution shift corresponds with minimum, not maximum, temperature tolerance

Rapid climate change may prompt species distribution shifts upward and poleward, but species movement in itself is not sufficient to establish climate causation. Other dynamics, such as disturbance history, may prompt species distribution shifts resembling those expected from rapid climate change. Links between species distributions, regional climate trends and physiological mechanism are needed to convincingly establish climate-induced species shifts. We examine a 38-year shift (1974-2012) in an elevation ecotone between two closely related ant species, Aphaenogaster picea and A. rudis. Even though A. picea and A. rudis are closely related with North American distributions that sometimes overlap, they also exhibit local- and regional-scale differences in temperature requirements so that A. rudis is more southerly and inhabits lower elevations whereas A. picea is more northerly and inhabits high elevations. We find considerable movement by the warm-habitat species upward in elevation between 1974 and 2012 with A. rudis, replacing the cold-habitat species, A. picea, along the southern edge of the Appalachian Mountain chain in north Georgia, USA. Concomitant with the distribution shifts, regional mean and maximum temperatures remain steady (1974-2012), but minimum temperatures increase. We collect individuals from the study sites and subject them to thermal tolerance testing in a controlled setting and find that maximum and minimum temperature acclimatization occurs along the elevation gradient in both species, but A. rudis consistently becomes physiologically incapacitated at minimum and maximum temperatures 2 °C higher than A. picea. These results indicate that rising minimum temperatures allow A. rudis to move upward in elevation and displace A. picea. Given that Aphaenogaster ants are the dominant woodland seed dispersers in eastern deciduous forests, and that their thermal tolerances drive distinct differences in temperature-cued synchrony with early blooming plants, these climate responses not only impact ant-ant interactions, but might have wide implications for ant-plant interactions.

GlobalAnts: a new database on the geography of ant traits (Hymenoptera: Formicidae)

In recent years the focus in ecology has shifted from species to a greater emphasis on functional traits. In tandem with this shift, a number of trait databases have been developed covering a range of taxa. Here, we introduce the GlobalAnts database. Globally, ants are dominant, diverse and provide a range of ecosystem functions. The database represents a significant tool for ecology in that it (i) contributes to a global archive of ant traits (morphology, ecology and life history) which complements existing ant databases and (ii) promotes a trait‐based approach in ant and other insect ecology through a broad set of standardised traits. The GlobalAnts database is unique in that it represents the largest online database of functional traits with associated georeferenced assemblage‐level data (abundance and/or occupancy) for any animal group with 9056 ant species and morphospecies records for entire local assemblages across 4416 sites. We describe the structure of the database, types of traits included and present a summary of data coverage. The value of the database is demonstrated through an initial examination of trait distributions across subfamilies, continents and biomes. Striking biogeographic differences in ant traits are highlighted which raise intriguing questions as to the mechanisms generating them.

Fire ants are drivers of biodiversity loss: a reply to King and Tschinkel (2013)

K A T H A R I N E L . S T U B L E,1 L A C Y D . C H I C K,1 M A R I A N O A . R O D R I G U E Z C A B A L,2 J E A N P H I L I P P E L E S S A R D3 and N A T H A N J . S A N D E R S1 1Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee, U.S.A., 2Department of Zoology, University of British Columbia, Vancouver, Canada and 3Quebec Centre for Biodiversity Science, Department of Biology, McGill University, Montreal, Canada

Departments Can Develop Teaching Identities of Graduate Students

Dear Editor: Reform of introductory science courses seeks to increase student retention and learning, yet faculty members are often unaware of modern teaching practices and/or not motivated to change their practices. Brownell and Tanner (2012) outlined another potential barrier: scientific professional identities are defined primarily by research and not by teaching. We think this is also an issue for graduate teaching assistants (GTAs), who play major roles in undergraduate science courses and represent the future of academic instruction. As graduate students interested in teaching, we call attention to the need for a national dialogue regarding development of GTA teaching identities. GTAs bear a heavy burden of implementing reformed curricula in introductory laboratories and discussions, often with little professional development. Although institutions may offer teaching orientations, these often focus on instructional policies and not on reformed teaching practices (Golde and Dore, 2001 ), potentially sending a message that teaching is more concerned with following institutional rules than fostering student learning. We think this is a lost opportunity to infuse universities across the country with a new generation of faculty who see teaching as an important part of their professional identities. We believe that science departments can develop GTAs’ professional identities as scholars and teachers by including teaching as part of the apprenticeship culture. GTAs develop research skills by taking classes, learning techniques, and applying this knowledge to their research with the support and feedback of a graduate committee and peers. Likewise, GTAs could take courses on effective teaching practices, be mentored, have their teaching evaluated by peers and faculty, and apply their teaching skills in increasingly independent instructional roles. A balanced research and teaching apprenticeship as a regular part of departmental practice could generate a new generation of faculty with professional identities as teachers and scholars. In this letter, we offer suggestions based on changes we are currently implementing in our department that may foster this teacher–scholar professional identity. To include teaching as part of the apprenticeship program, a committee of faculty and experienced GTAs should oversee graduate teaching. In our department, GTA research and teaching are both overseen by a graduate affairs committee. We are separating the teaching and research oversight into separate committees, so the teaching aspect of the committee is not subsumed by a focus on research. This graduate teaching committee (GTC) will make teaching assignments, conduct and review assessments of teaching, and provide opportunities for teaching seminars. The GTC will make teaching assignments with professional development of teaching in mind, as opposed to solely considering departmental need. Yearly information regarding each graduate students teaching experience, teaching assessment results, and future teaching goals will be collected by the GTC. The GTC will then match the teaching skills of each GTA with available courses. For example, a laboratory class with a defined curriculum and more faculty oversight may require less pedagogical skill and be more appropriate for a new GTA than a discussion class would be. In our department, the only teaching feedback GTAs currently receive is the numeric and written responses from university student evaluations. In upcoming years, GTAs will be required to have a yearly observation of their teaching by a peer GTA mentor and the faculty for whom they teach. GTAs and their peer mentors will analyze the teaching observations and student evaluations and submit a summary teaching statement to the GTC each year. We believe this will encourage reflective practice, and these statements can be used by the GTC to make future teaching assignments. GTAs who receive positive evaluations by the GTC, peers, and faculty will have the option to teach courses in which they would act with more instructional autonomy, including being lecture assistants and possibly course instructors, and will qualify to serve as peer mentors. GTAs with the highest instructional skills and interest in teaching could become involved in departmental curriculum reform, a role often reserved for faculty. In addition to the teaching orientations currently offered by the institution and division of biology, we have recommended that our department initiate a first-year seminar series led by experienced GTAs or faculty. The first seminar would focus on science communication skills and the second on modern teaching practices. These seminars would also provide a forum for discussing first-year teaching challenges and successes. However, due to heavy course work demands in the first year of our graduate program, these seminars may be held in the second year and modified to better match the teaching needs of second-year GTAs. Development of teaching abilities may help GTAs balance research and teaching responsibilities throughout their academic careers by fostering a professional identity that supports both aspects of an academic life (French and Russell, 2002 ; Feldon et al., 2011 ). We believe that graduates with these professional identities could be more competitive for faculty positions and that this system would foster a generation of faculty capable of enacting undergraduate science education reforms.

Forest invader replaces predation but not dispersal services by a keystone species

Invasive species generally occur and thrive in human-disturbed ecosystems, but Brachyponera chinensis (Asian needle ant, formerly ‘Pachycondyla chinensis’) also invades intact forests. The invasion into native habitats potentially puts B. chinensis in direct competition with the keystone seed-dispersing ants in the genus Aphaenogaster. We observed B. chinensis colonizing artificial nests placed in deciduous forest of the north Georgia Piedmont (US). Their presence appeared to displace existing Aphaenogaster rudis and Reticulitermes flavipes (subterranean termite) colonies. We subsequently mapped the B. chinensis invasion as well as co-existing A. rudis and R. flavipes colonies by examining coarse woody material (CWM) for nesting colonies. We tested whether the B. chinensis invasion changed with forest microclimates, covaried with A. rudis and/or R. flavipes occurrence, and whether it was associated with failed dispersal of a dominant understory herb. Our results and observations suggest that B. chinensis shares ecological niche requirements (temperature, moisture and CWM as nesting habitat) with A. rudis, severely diminishing the abundance of this native ant. In supplanting A. rudis, B. chinensis appears to play an equivalent role to A. rudis as a termite predator, but fails as a seed disperser. Essentially, the invader substitutes for the negative but not the positive species interactions, thereby apparently shifting ecological dynamics in the invaded system.

The Janus of macrophysiology: stronger effects of evolutionary history, but weaker effects of climate on upper thermal limits are reversed for lower thermal limits in ants

Abstract Species may exhibit similar traits via different mechanisms: environmental filtering and local adaptation (geography) and shared evolutionary history (phylogeny) can each contribute to the resemblance of traits among species. Parsing trait variation into geographic and phylogenetic sources is important, as each suggests different constraints on trait evolution. Here, we explore how phylogenetic distance, geographic distance, and geographic variation in climate shape physiological tolerance of high and low temperatures using a global dataset of ant thermal tolerances. We found generally strong roles for evolutionary history and geographic variation in temperature, but essentially no detectable effects of spatial proximity per se on either upper or lower thermal tolerance. When we compared the relative importance of the factors shaping upper and lower tolerances, we found a much stronger role for evolutionary history in shaping upper versus lower tolerance, and a moderately weaker role for geographic variation in temperature in shaping upper tolerance when compared with lower tolerance. Our results demonstrate how geographic variation in climate and evolutionary history may have differential effects on the upper and lower endpoints of physiological tolerance. This Janus effect, where the relative contributions of geographic variation in climate and evolutionary history are reversed for lower versus upper physiological tolerances, has gained some support in the literature, and our results for ant physiological tolerances provide further evidence of this pattern. As the climate continues to change, the high phylogenetic conservatism of upper tolerance may suggest potential constraints on the evolution of tolerance of high temperatures.

Heat tolerance predicts the importance of species interaction effects as the climate changes

SYNOPSIS Few studies have quantified the relative importance of direct effects of climate change on communities versus indirect effects that are mediated thorough species interactions, and the limited evidence is conflicting. Trait-based approaches have been popular in studies of climate change, but can they be used to estimate direct versus indirect effects? At the species level, thermal tolerance is a trait that is often used to predict winners and losers under scenarios of climate change. But thermal tolerance might also inform when species interactions are likely to be important because only subsets of species will be able to exploit the available warmer climatic niche space, and competition may intensify in the remaining, compressed cooler climatic niche space. Here, we explore the relative roles of the direct effects of temperature change and indirect effects of species interactions on forest ant communities that were heated as part of a large-scale climate manipulation at high- and low-latitude sites in eastern North America. Overall, we found mixed support for the importance of negative species interactions (competition), but found that the magnitude of these interaction effects was predictable based on the heat tolerance of the focal species. Forager abundance and nest site occupancy of heat-intolerant species were more often influenced by negative interactions with other species than by direct effects of temperature. Our findings suggest that measures of species-specific heat tolerance may roughly predict when species interactions will influence responses to global climate change.

Evolution of thermal tolerance and its fitness consequences: parallel and non-parallel responses to urban heat islands across three cities

The question of parallel evolution—what causes it, and how common it is—has long captured the interest of evolutionary biologists. Widespread urban development over the last century has driven rapid evolutionary responses on contemporary time scales, presenting a unique opportunity to test the predictability and parallelism of evolutionary change. Here we examine urban evolution in an acorn-dwelling ant species, focusing on the urban heat island signal and the ants tolerance of these altered urban temperature regimes. Using a common-garden experimental design with acorn ant colonies collected from urban and rural populations in three cities and reared under five temperature treatments in the laboratory, we assessed plastic and evolutionary shifts in the heat and cold tolerance of F1 offspring worker ants. In two of three cities, we found evolved losses of cold tolerance, and compression of thermal tolerance breadth. Results for heat tolerance were more complex: in one city, we found evidence of simple evolved shifts in heat tolerance in urban populations, though in another, the difference in urban and rural population heat tolerance depended on laboratory rearing temperature, and only became weakly apparent at the warmest rearing temperatures. The shifts in tolerance appeared to be adaptive, as our analysis of the fitness consequences of warming revealed that while urban populations produced more sexual reproductives under warmer laboratory rearing temperatures, rural populations produced fewer. Patterns of natural selection on thermal tolerances supported our findings of fitness trade-offs and local adaptation across urban and rural acorn ant populations, as selection on thermal tolerance acted in opposite directions between the warmest and coldest rearing temperatures. Our study provides mixed support for parallel evolution of thermal tolerance under urban temperature rise, and, importantly, suggests the promising use of cities to examine parallel and non-parallel evolution on contemporary time scales.

Thermal specialist ant species have restricted, equatorial geographic ranges: implications for climate change vulnerability and risk of extinction

Why do species exist some places but not others? This question arguably lies at the core of ecology and evolutionary biology, and a number of hypotheses have been put forward to explain the remarkable diversity in geographic range and distribution among species. The niche breadth hypothesis – that evolved increases in environmental tolerance permit larger geographic ranges than species with more narrow tolerances – is generally well-supported (Slatyer et al. 2013), but there are a number of limitations on how environmental tolerances are assessed and the spatial and taxonomic replication of these data. The question of whether there exist broad-scale taxonomic and geographic relationships between tolerance breadth and range size has become increasingly salient as the world experiences rapid changes in climate. Small-ranged species are frequently more prone to extinction under environmental perturbation (Purvis et al. 2000), and as a consequence may be more vulnerable to global climate change. Comparisons of tolerance breadth and range size can therefore yield important biological insights into the determinants of species ranges and their vulnerability to climate change. We developed a global dataset of ant thermal tolerances and geographic range size and latitudinal position and found that species with narrow thermal tolerance breadths had restricted, more equatorially positioned geographic ranges, suggesting tropical thermal specialists are at greater risk of extinction under climate change.

Evolution of plasticity in the city: urban acorn ants can better tolerate more rapid increases in environmental temperature

Cities often warm at faster rates during the day and across space. The mechanisms underlying how organisms respond to these climatic changes in cities are largely unknown. This study finds evidence that the heat tolerance of an acorn-dwelling ant species has evolved rapidly to cope with these faster rates of urban warming.