David A. Holway's research while affiliated with University of California, San Diego and other places

Publications (129)

Article
Full-text available
Non-native plant species can disrupt plant–pollinator interactions by altering pollinator foraging behavior, which can in turn affect levels of interspecific pollen transfer between native and non-native plant species. These processes may be amplified in cases where introduced plant species act as magnet taxa that enhance pollinator visitation to o...
Preprint
Full-text available
The ecological effects of species introductions can change over time, but an understanding of how and why they do remains hindered by the lack of long-term data sets that permit investigation into underlying causes. We employed stable isotope analysis to estimate how trophic position changes as a function of time for the Argentine Ant, a widespread...
Article
Full-text available
Global climate change is causing more frequent and severe droughts, which could have serious repercussions for the maintenance of biodiversity. Here, we compare native bee assemblages collected via bowl traps before and after a severe drought event in 2014 in San Diego, California, and examine the relative magnitude of impacts from drought in fragm...
Article
Recent work underscores that ants are highly proficient and ubiquitous scavengers. These tendencies extend to numerically and behaviorally dominant introduced ants, which exhibit a suite of traits that allow them to exploit and monopolize carrion to a greater extent than is widely appreciated. We thus contend that an understanding of how introduced...
Article
Full-text available
Biological invasions are a leading cause of global change, yet their long‐term effects remain hard to predict. Invasive species can remain abundant for long periods of time, or exhibit population crashes that allow native communities to recover. The abundance and impact of non‐native species may also be closely tied to temporally variable habitat c...
Article
Many walking insects use vision for long-distance navigation, but the influence of vision on rapid walking performance that requires close-range obstacle detection and directing the limbs towards stable footholds remains largely untested. We compared Argentine ant ( Linepithema humile ) workers in light versus darkness while traversing flat and une...
Preprint
Many walking insects use vision for long-distance navigation, but the influence of vision in detecting close-range obstacles and directing the limbs to maintain stability remains largely untested. We compared Argentine ant workers in light versus darkness while traversing flat and uneven terrain. In darkness, ants reduced flat-ground walking speeds...
Article
Full-text available
Predicting changes in the abundance and distribution of introduced species over time is difficult, but clues regarding the underlying causes of these changes may come from long-term surveys. Resurveys conducted over large spatial scales, for example, can be used to discriminate between site-specific causes of decline and those that act at the popul...
Article
Full-text available
Natural terrain is rarely flat. Substrate irregularities challenge walking animals to maintain stability, yet we lack quantitative assessments of walking performance and limb kinematics on naturally uneven ground. We measured how continually uneven 3D-printed substrates influence walking performance of Argentine ants by measuring walking speeds of...
Article
Full-text available
Ecological impacts associated with ant introductions have received considerable attention, but most studies that report on these impacts contrast species assemblages between invaded and uninvaded sites. Given the low inferential power of this type of space-for-time comparison, alternative approaches are needed to evaluate claims that ant invasions...
Preprint
Full-text available
Natural terrain is rarely flat. Substrate irregularities challenge walking animals to maintain stability, yet we lack quantitative assessments of walking performance and limb kinematics on naturally rough ground. We measured how continually rough 3D-printed substrates influence walking performance of Argentine ants by measuring walking speeds of wo...
Article
Predicting the long‐term consequences of habitat alteration for the preservation of biodiversity and ecosystem function requires an understanding of how ecological filters drive taxonomic and functional biodiversity loss. Here, we test a set of predictions concerning the role of ecological filters in restructuring native bee assemblages inhabiting...
Article
The Argentine ant, Linepithema humile (Mayr), is a highly invasive ant species that has spread into urban, agricultural, and natural areas worldwide. The pervasive expansion of this species is detrimental both ecologically and economically, resulting in the allocation of vast amounts of resources for control. New efforts are underway to control the...
Article
Most plant–pollinator mutualisms are generalized. As such, they are susceptible to perturbation by abundant, generalist, non-native pollinators such as the western honey bee (Apis mellifera), which can reach high abundances and visit flowers of many plant species in their expansive introduced range. Despite the prevalence of non-native honey bees,...
Article
The ecological effects of species introductions can change in magnitude over time, but an understanding of how and why they do so remains incompletely understood. Clarifying this issue requires consideration of how temporal variation in invader traits affects invasion impacts (e.g., through differential effects on the diversity and composition of n...
Article
The western honey bee (Apis mellifera) is the most frequent floral visitor of crops worldwide, but quantitative knowledge of its role as a pollinator outside of managed habitats is largely lacking. Here we use a global dataset of 80 published plant-pollinator interaction networks as well as pollinator effectiveness measures from 34 plant species to...
Article
Full-text available
Pollination services are compromised by habitat destruction, land-use intensification, pesticides, and introduced species. How pollination services respond to such stressors depends on the capacity of pollinator assemblages to function in the face of environmental disruption. Here, we quantify how pollination services provided to a native plant cha...
Preprint
Full-text available
An understanding of why introduced species achieve ecological success in novel environments often requires information about the factors that limit the abundance of these taxa in their native ranges. Although numerous recent studies have evaluated the importance of natural enemies in this context, relatively few have examined how ecological success...
Data
Description and explanation of study sites. (PDF)
Article
Full-text available
Despite a large number of ecological studies that document diversity loss resulting from anthropogenic disturbance, surprisingly few consider how disturbance affects temporal patterns of diversity that result from seasonal turnover of species. Temporal dynamics can play an important role in the structure and function of biological assemblages. Here...
Data
List of study plots in coastal sage scrub reserves and habitat fragments. (PDF)
Data
Species list of bees collected in this study. (PDF)
Article
Full-text available
The Argentine ant (Linepithema humile) is a widespread, abundant and ecologically disruptive invader that is present throughout major portions of coastal California and on half of the California Channel Islands. On Santa Cruz Island, the Argentine ant had invaded about 2% of the island's area in four distinct locations as of 2012. Given the negativ...
Article
Full-text available
The functions and compositions of symbiotic bacterial communities often correlate with host ecology. Yet cause-and-effect relationships, and the order of symbiont versus host change, remain unclear in the face of ancient symbioses and conserved host ecology. Several groups of ants exemplify this challenge, as their low-nitrogen diets and specialize...
Article
1. Although plant invasions often reduce insect abundance and diversity, non‐native plants that support phytophagous insects can subsidise higher trophic levels via elevated herbivore abundance. 2. Here ant–aphid interactions on non‐native fennel on Santa Cruz Island, California are examined. Fennel hosts abundant, honeydew‐producing fennel aphids....
Article
1. Bees are ecologically important pollinators that are threatened by disease, habitat degradation, and habitat loss. Bee species that share ecological traits (e.g. body size, diet breadth, and sociality) may often respond similarly to environmental disturbance; however, few studies have examined the extent to which closely related, ecologically si...
Article
Ants often visit flowers, but have only seldom been documented to provide effective pollination services. Floral visitation by ants can also compromise plant reproduction in situations where ants interfere with more effective pollinators. Introduced ants may be especially likely to reduce plant reproductive success through floral visitation, but ex...
Article
Full-text available
Resource availability can determine an organism's investment strategies for growth and reproduction. When nutrients are limited, there are potential tradeoffs between investing into offspring number versus individual offspring size. In social insects, colony investment in offspring size and number may shift in response to colony needs and the avail...
Article
1. Ant–plant mutualisms have been the focus of considerable empirical research, but few studies have investigated how introduced ants affect these interactions. Using 2 years of survey data, this study examines how the introduced Argentine ant [Linepithema humile (Mayr)] differs from native ants with respect to its ability to protect the extraflora...
Article
Invasions give rise to a wide range of ecological effects. Many invasions proceed without noticeable impacts on the resident biota, whereas others shift species composition and even alter ecosystem function. Ant invasions generate a broad spectrum of ecological effects, but controversy surrounds the extent of these impacts, especially with regard t...
Article
For plant species that depend on animal-mediated pollination, reproduction hinges on adequate access to pollinators. Even in the presence of intact pollinator assemblages, negative interactions among floral visitors can compromise pollination services. Ants, for example, visit flowers and can discourage visitation by other insects, but usually do n...
Conference Paper
Background/Question/Methods Urbanization often reduces pollinator diversity. Although specific life-history traits may allow certain pollinator species to tolerate anthropogenic disturbance, even outwardly similar species can exhibit divergent responses to land-use change. Here, we use GIS to identify landscape-level correlates of occurrence for...
Conference Paper
For plant species that depend on animal-mediated pollination, reproduction hinges on adequate access to pollinators. Even in the presence of intact pollinator assemblages, negative interactions among floral visitors can compromise pollination services. Ants, for example, visit flowers and can discourage visitation by other insects, but usually do n...
Article
Full-text available
Arthropods have been understudied on Santa Cruz Island, resulting in an incomplete understanding of these diverse and ecologically important members of island ecosystems. To enhance the current understanding of Santa Cruz Island biodiversity, we sampled arthropods in 2 native plant habitats: island scrub oak (Quercus pacifica) woodland and patches...
Article
Protection mutualisms between ants and honeydew-producing insects influence arthropod food webs by altering the behaviour, activity and local abundance of ants on plants. Ants often tend multiple species of honeydew-producing insects; however, studies that examine such effects typically consider only pairwise mutualisms. This study investigates how...
Conference Paper
Background/Question/Methods Introduced ants frequently enter into mutualisms with plants and other insects to obtain carbohydrate-rich resources. This phenomenon can disrupt mutualisms to the detriment of mutualist partners as well as give rise to ecological effects external to the mutualism itself. Observations of Argentine ant workers harassing...
Conference Paper
Background/Question/Methods Invasive ants often form protection mutualisms with plants or insects that offer sugar-rich food rewards. The infiltration of mutualisms by non-native ants can disrupt such interactions, and negatively affect mutualist partners and give rise to broader ecological effects. Here we examine how the Argentine ant affects d...
Conference Paper
Background/Question/Methods Evidence is mounting that pollinator assemblages are affected by human activities such as urbanization. Recent meta-analyses reveal that human-mediated habitat degradation tends to decrease pollinator diversity and preferentially extirpate specialist pollinators. However, few studies have examined how disturbance affect...
Conference Paper
Background/Question/Methods The displacement of native ants by the Argentine ant is well documented, but much less is known about how non-ant arthropods respond following invasion. Unlike the native ants they displace, the Argentine ant can attain exceptionally high densities, remain active year round, and form spatially expansive supercolonies....
Article
Mounting evidence indicates that trade-offs between plant defense and reproduction arise not only from resource allocation but also from interactions among mutualists. Indirect costs of plant defense by ants, for example, can outweigh benefits if ants deter pollinators. Plants can dissuade ants from occupying flowers, but such arrangements may brea...
Conference Paper
Full-text available
Body size is an important life history trait that figures directly into the ecology, physiology, behavior and survival of an organism. For social insects, body size can vary at the individual level (worker size) and the colony level (distributions of workers body sizes). Variation in body size is potentially optimized in response to environment flu...
Article
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Animals frequently experience resource imbalances in nature. For ants, one resource that may be particularly valuable for both introduced and native species is high-carbohydrate honeydew from hemipteran mutualists. We conducted field and laboratory experiments: (1) to test if red imported fire ants (Solenopsis invicta) competed with native ants for...
Poster
Background/Question/Methods Studies of mutualistic interactions generally focus on each member within the partnership but often do not consider the broader ecological consequences of mutualisms. These ecological effects can be important; mutualisms can influence the structure of food webs. Previous studies of ant-hemipteran mutualisms have shown...
Article
Full-text available
Mutualisms play key roles in the functioning of ecosystems. However, reciprocally beneficial interactions that involve introduced species also can enhance invasion success and in doing so compromise ecosystem integrity. For example, the growth and competitive ability of introduced plant species can increase when fungal or microbial associates provi...
Conference Paper
In southern California, the coast barrel cactus (Ferocactus viridescens) produces extrafloral nectar (EFN) attractive to ants, including the invasive Argentine ant (Linepithema humile). Ants discourage a prevalent herbivore, a leaf-footed bug (Narnia wilsoni), from feeding on cacti, and increasing bug presence reduces cactus seed mass, a variable c...
Conference Paper
Background/Question/Methods In the last decade mutualisms have been affirmed as important ecological drivers with impacts resonating beyond pairwise interactions to entire ecosystems. As a result, mutualisms with a long history of research are being evaluated for their role in structuring food webs. Ants and honeydew-producing Hemiptera participa...
Article
1. In ant–hemipteran mutualisms, ants receive carbohydrates in the form of honeydew, while hemipterans receive protection from natural enemies. In the absence of natural enemies, however, the direct effects of tending are generally less well known. We hypothesised that with increasing tending intensity (ant to aphid ratio), aphid performance would...
Article
Flooding impacts ground nesting ant colonies by destroying the infrastructure housing and organizing societal function. Here, we report the convergent evolution in distantly related ant species of a behavioral trait that minimizes costs of flooding: the construction of earthen levees around nest entrances. In a South American floodplain ecosystem,...
Article
Many arthropods engage in mutualisms in which they consume plant-based foods including nectar, extrafloral nectar, and honeydew. However, relatively little is known about the manner in which the specific macronutrients in these plant-based resources affect growth, especially for carnivorous arthropods. Using a combination of laboratory and field ex...
Article
Full-text available
Studies of food webs often employ stable isotopic approaches to infer trophic position and interaction strength without consideration of spatio-temporal variation in resource assimilation by constituent species. Using results from laboratory diet manipulations and monthly sampling of field populations, we illustrate how nitrogen isotopes may be use...
Article
Obtaining quantitative information concerning pollinator behaviour has become a primary objective of pollination studies, but methodological limitations hinder progress towards this goal. Here, we use molecular genetic methods in an ecological context to demonstrate that endemic Hawaiian Hylaeus bees (Hymenoptera: Colletidae) selectively collect po...
Article
Variation in invasion success may result from the divergent evolutionary histories of introduced species compared to those of native taxa. The vulnerability of native biotas to ecological disruption may be especially great on oceanic islands invaded by continental species with unique ecological traits. In part because Hawaii lacks native eusocial i...
Article
The difficulty of directly observing predatory events hinders a complete understanding of how predation structures food webs. Indirect approaches such as PCR-based and isotopic analyses clarify patterns of resource consumption but fail to distinguish predation from scavenging. Given that facultative scavenging is a ubiquitous and phylogenetically w...
Article
Food availability often influences competitive outcomes through effects on consumer growth. Although it has received less attention, food availability may also affect competition through nutritional effects on behavior. One hypothesis linking nutrition and competition in ants posits that increased access to carbohydrates favors greater investment i...
Chapter
A comprehensive understanding of the causal factors that promote invasiveness, as well as the mechanisms that mediate the invasion process, should assist in developing a predictive capacity about which species are likely to become invasive in which habitats. Most invasive ants studied to date appear to be pre-adapted to some degree for periodic dis...
Article
Plant invasions have tremendous potential to alter food webs by changing basal resources. Recent studies document how plant invasions may contribute to increased arthropod abundances in detritus-based food webs. An obvious mechanism for this phenomenon-a bottom-up effect resulting from elevated levels of detritus from the invasive plant litter-has...
Conference Paper
Background/Question/Methods Invasive species disrupt ecosystems through multiple mechanisms. This study examines the impact of a social wasp invader, Vespula pensylvanica, on two radiations of Hawaiian Hymenoptera: Hylaeus bees and Nesodynerus wasps. Because Hawaii has no native social insects, endemic solitary bees and wasps may be particularly s...
Conference Paper
Background/Question/Methods Mutualisms have the potential to aid in the success and spread of invasive species. Several species of invasive ants engage in food-for-protection mutualisms with honeydew-producing hemipterans and plants with extrafloral nectaries. In the US, the red imported fire ant, Solenopsis invicta, and Argentine ant, Linepithema...
Conference Paper
Background/Question/Methods Invasive species alter the dynamics of mutualisms when quantitative or qualitative differences exist between native participants and invaders. Invasive ants are of interest in this respect because they often become more abundant and exhibit higher levels of aggression compared to the native ants they replace. In food-for...
Conference Paper
Background/Question/Methods - Food availability often influences competitive outcomes through differential effects on growth and reproductive output. Although it has received less attention, resource conditions may also influence competition through nutritional effects on behavioral performance. The link between nutrition and competition may be par...
Article
An unresolved question in ecology concerns why the ecological effects of invasions vary in magnitude. Many introduced species fail to interact strongly with the recipient biota, whereas others profoundly disrupt the ecosystems they invade through predation, competition, and other mechanisms. In the context of ecological impacts, research on biologi...
Article
Aim Species distribution models (SDMs) or, more specifically, ecological niche models (ENMs) are a useful and rapidly proliferating tool in ecology and global change biology. ENMs attempt to capture associations between a species and its environment and are often used to draw biological inferences, to predict potential occurrences in unoccupied reg...
Conference Paper
Full-text available
Mutualisms may encourage the success and spread of invasive species. Invasive ants engage in food-for-protection mutualisms with honeydew-producing hemipterans and plants with extrafloral nectaries. For example, the red imported fire ant, Solenopsis invicta, frequently associates with aphids, scales and mealybugs in the southern US. However, few st...
Conference Paper
The introduction of non-native organisms is a leading cause of species imperilment. This study examines the impact of a social wasp invader, Vespula pensylvanica, on two groups of native Hymenoptera: Hylaeus bees and Odynerus wasps, which represent two major insect radiations in Hawaii. Because Hawaii has no native social insects, endemic solitary...
Article
Full-text available
Baker and Stebbins's 1965 book The Genetics of Colonizing Species aimed to draw together scientists from a variety of disciplines to provide a conceptual framework for the study of species introductions. A goal of their volume was to examine how studies on biological invasions could be used to provide insight into basic research questions as well a...
Article
Social insects can modulate body temperature to increase foraging efficiency; however, little is known about how the relative value of protein resources affects forager body temperature. Such regulation may be important given that colony growth is often limited by protein availability. In this paper, we present what are, to our knowledge, the first...