Abundance Of Host Species Research Articles

The Allee effect in hosts can weaken the dilution effect of host diversity on parasitoid infections

Although numerous studies have shown disease prevalence to be influenced by changes in biodiversity, few studies have explored which factors affect the relationship between biodiversity and disease. When species richness increases, the abundance of host species decreases due to the limited available resources. Low population density may yield a low population growth rate and a high chance of extinction caused by a variety of mechanisms such as mate limitation and inefficient cooperative defense/breeding, i.e. the Allee effect. However, few studies investigating the diversity-disease relationship have taken the Allee effect into account. Here, using a multi-host-parasitoid model, we found that the Allee effect can weaken the host dilution effect, to a degree that depended on the strength of the Allee effect and the aggregation of parasitoid attack. The Allee effect within hosts can protect them from being parasitized and increase the risk of host-parasitoid system collapse. These results may provide an alternative explanation for non-linear relationships between biodiversity and parasitic disease prevalence, and, therefore, can contribute to reconciliation of current disputes over dilution effects.

Effects of land use on zoonotic host communities: a global correlative analysis

BackgroundEnvironmental trade-offs associated with land use—for example, between food security and biodiversity conservation—are crucial dimensions of planetary health. Land use-driven biodiversity change might predictably affect disease risk if reservoir host species are consistently more likely to persist under human disturbance (ie, if ecological communities in modified habitats generally have a higher zoonotic potential than those in unmodified habitats). Such a phenomenon has been observed in specific disease systems, but with substantial change in global land use projected for this century, assessing its global and taxonomic generality would shed light on an important hypothesised driver of environmental synergies or trade-offs between conservation and public health. MethodsWe collated data on hosts of human parasites and pathogens from the published literature, and combined these with the Projecting Responses of Ecological Diversity in Changing Terrestrial Systems (PREDICTS) global database of local ecological communities and associated land use data. We analysed the effects of land use on host richness and abundance across 7330 sites globally, controlling for disease-related research effort and differences in survey methods. FindingsEcological communities in anthropogenic land uses (managed and urban ecosystems) contained a consistently higher richness and abundance of host species than did communities in nearby primary (undisturbed) sites. However, among mammal hosts of zoonotic pathogens, we found considerable taxonomic variation in host responses to land use, with abundances of rodents and bats generally increasing and those of primates and carnivores generally declining in modified landscapes. InterpretationOur results suggest that future change in global land use has the potential to drive overall increasing contact between people and ecological communities with increased shared pathogen potential (ie, more potential hosts and possible opportunities for transmission). However, the differences in host responses to modified landscapes among mammal orders suggests that these changes are unlikely to affect all zoonotic diseases consistently. This result supports arguments that, rather than expecting a consistent relationship between biodiversity change and disease, in practice, policies aiming both to conserve biodiversity and reduce human disease (eg, through establishment of protected areas) must be disease and context specific. FundingThis research was supported by a Graduate Research Scholarship from University College London (to RG), the Natural Environment Research Council (to DWR and KEJ), and a Royal Society University Research Fellowship (to TN).

Ixodes scapularis (Acari: Ixodidae) Reservoir Host Diversity and Abundance Impacts on Dilution of Borrelia burgdorferi (Spirochaetales: Spirochaetaceae) in Residential and Woodland Habitats in Connecticut, United States.

The dilution effect in the zoonotic disease transmission cycle theorizes that an increased diversity of host species will alter transmission dynamics, result in a decrease in pathogen prevalence, and potentially lower human disease incidence. The interrelationship of Borrelia burgdorferi (Johnson, Schmid, Hyde, Steigerwalt, and Brenner) (Spirochaetales: Spirochaetaceae), the etiological agent of Lyme disease (LD), and its primary vector, blacklegged ticks (Ixodes scapularis Say) (Acari: Ixodidae), is a commonly used example of the dilution effect, suggesting that an increased diversity of host species will be found in large, undisturbed forested tracts and lower diversity in fragmented forests. Given that Connecticut woodlands are mature with heavy upper canopies and generally poor habitat quality, we hypothesized there would be higher diversity of host species resulting in lower prevalence of B. burgdorferi in white-footed mice (Peromyscus leucopus Rafinesque) (Rodentia: Cricetidae) in forested residential areas. Using camera and live small mammal trapping techniques, we determined there was a greater richness of reservoir host species, significantly higher encounters with hosts, and significantly lower B. burgdorferi host-infection in residential areas as compared to large, intact forested stands. Furthermore, we determined that the driving factor of pathogen dilution was not host species diversity, but rather overall encounter abundance with alternative hosts, regardless of habitat type. Our study challenges major concepts of the dilution effect within the Connecticut landscape and calls for new managerial actions to address the current state of our woodlands and abundance of host species in the interest of both forest and public health.

The mating system of the symbiotic pea-crab Dissodactylus crinitichelis (Brachyura, Pinnotheridae): monogamy or promiscuity?

The mating systems of symbiotic crustaceans vary broadly, ranging from monogamy to polygamy to promiscuity. This disparity in mating systems coupled with wide differences in host ecology provides opportunities to study the effect of environmental conditions on the social behavior of marine organisms. In this study, we tested the prediction that symbiotic crustaceans inhabiting relatively large and abundant host species are promiscuous rather than monogamous. The host traits above constraint host monopolization and favor host-switching behaviors by males individuals and, thus, ultimately drive promiscuity as a mating system in symbiotic crustaceans. As a model system we used Dissodactylus crinitichelis, a small ‘pea-crab’ that inhabits the relatively large and abundant sand dollar Encope emarginata. We described the population distribution of D. crinitichelis at two intertidal localities in Sergipe, Brazil, and conducted laboratory experiments to infer the mating system of this species. Dissodactylus crinitichelis inhabit sand dollars as adult heterosexual pairs more frequently than expected by chance alone, but these heterosexual pairs did not exhibit size-assortative pairing. Sexual dimorphism was reversed in D. crinitichelis, with males attaining smaller average body sizes than females but exhibiting more elaborated weaponry (male > female claws). These findings disagree with expectations for monogamous symbiotic crustaceans. Laboratory experiments demonstrated that male and female crabs switch among host individuals rather frequently and heterosexual pairs retrieved from the field did not remain together for long times. Our results argue against social monogamy and in favor of promiscuity in D. crinitichelis. Our study supports the notion that host abundance and large body size (relative to that of symbiotic guests) favor promiscuity in symbiotic crustaceans.

Mapping of the Asian longhorned beetle’s time to maturity and risk to invasion at contiguous United States extent

Anoplophora glabripennis, the Asian Longhorned Beetle (ALB), is an invasive species of high economic and ecological relevance given the potential it has to cause tree damage, and sometimes mortality, in the United States. Because this pest is introduced by transport in wood-packing products from Asia, ongoing trade activities pose continuous risk of transport and opportunities for introduction. Therefore, a geographic understanding of the spatial distribution of risk factors associated with ALB invasions is needed. Chief among the multiple risk factors are (a) the potential for infestation based on host tree species presence/absence, and (b) the temperature regime as a determinant of ALB’s growth time to maturity. This study uses an empirical model of ALB’s time to maturity as a function of temperature, along with a model of heat transfer in the wood of the host and spatial data describing host species presence/absence data, to produce a map of risk factors across the conterminous United States to define potential for ALB infestation and relative threat of impact. Results show that the region with greatest risk of ALB infestation is the eastern half of the country, with lower risk across most of the western half due to low abundance of host species, less urban area, and prevalence of cold, high elevations. Risk is high in southeastern states primarily because of temperature, while risk is high in northeastern and northern central states because of high abundance of host species.

Avoidance of host resistance in the oviposition-site preferences of rose bitterling

A contemporary outcome of dynamic host–parasite coevolution can be driven by the adaptation of a parasite to exploit its hosts at the population and species levels (parasite specialisation) or by local host adaptations leading to greater host resistance to sympatric parasite populations (host resistance). We tested the predominance of these two scenarios using cross-infection experiments with two geographically distant populations of the rose bitterling, Rhodeus ocellatus, a fish brood parasite of freshwater mussels, and four populations of their mussel hosts (two Anodonta woodiana and two Unio douglasiae populations) with varying degrees of geographic sympatry and local coexistence. Our data support predictions for host resistance at the species level but no effect of local coexistence between specific populations. Rhodeus ocellatus showed a preference for allopatric host populations, irrespective of host species. Host mussel response, in terms of ejection of R. ocellatus eggs, was stronger in the more widespread and abundant host species (A. woodiana) and this response tended to be higher in sympatric populations. These outcomes provide support for the importance of host resistance in bitterling oviposition-site decisions, demonstrating that host choice by R. ocellatus is adaptive by minimizing egg ejections. These findings imply that R. ocellatus, and potentially other bitterling species, may benefit from exploiting novel hosts, which may not possess appropriate adaptive responses to parasitism.

The Roles of Trophic Interactions, Competition and Landscape in Determining Metacommunity Structure of a Seed-Feeding Weevil and Its Parasitoids

Community composition is determined by attributes of the environment, individual species, and interactions among species. We studied the distributions of a seed weevil and its parasitoid and hyperparasitoid wasps in a fragmented landscape. The occurrence of the weevil was independent of the measured attributes of the landscape (patch connectivity and resource availability). However, between habitat-patch networks, weevil density decreased with increasing parasitism, suggesting top-down control, especially in the north. Parasitism was mostly due to a specialist and a generalist that appeared to compete strongly. This competitive interaction was strongest at high patch-connectivity, perhaps due to a trade-off of local competitive ability and dispersal. Finally, the abundance of the generalist hyperparasitoid was unrelated to landscape or host-species abundance. The snapshot presented by these data can best be explained by top-down effects, interactions among species, host ranges, and patch configuration in ...

Prevalence of avian haemosporidian parasites is positively related to the abundance of host species at multiple sites within a region.

Parasite prevalence is thought to be positively related to host population density owing to enhanced contagion. However, the relationship between prevalence and local abundance of multiple host species is underexplored. We surveyed birds and their haemosporidian parasites (genera Plasmodium and Haemoproteus) at multiple sites across eastern North America to test whether the prevalence of these parasites in a host species at a particular site is related to that host's local abundance. Prevalence was positively related to host abundance within most sites, although the effect was stronger and more consistent for Plasmodium than for Haemoproteus. In contrast, prevalence was not related to variation in the abundance of most individual host species among sites across the region. These results suggest that parasite prevalence partly reflects the relative abundances of host species in local assemblages. However, three nonnative host species had low prevalence despite being relatively abundant at one site, as predicted by the enemy release hypothesis.

Seasonal variations of host resources influence foraging strategy in parasitoids

AbstractMany species have to cope with decreased resource availability and life expectancy during winter. The optimal foraging theory predicts that under these conditions, generalist foraging strategies should be favoured, via the acceptance of suboptimal resources. In contrast, during favourable seasons, specialist foraging strategies, i.e., a preferential consumption of the most profitable resources, should be favoured instead. Although spatial and fine‐scale temporal dimensions of the influence of resource distribution on foraging strategies have long been studied in individual species, guild‐level, large‐scale temporal approaches (over multiple seasons) have rarely been considered. Parasitoids that can remain active during winter are an interesting model system which allows direct testing of resource profitability and reaching conclusions about foraging strategies from an evolutionary point of view. Here, we analysed how temporal variations of host resource availability in northwestern France impact the foraging strategies of parasitoid wasps. The foraging behaviours of dominant cereal aphid parasitoid species in relation to the two most abundant aphid host species were observed in winter and in spring. Because of a seasonal change in the host–parasitoid community and of a few species present in the fields each season, we were unable to confirm our hypothesis at the species level for all the studied species. Nevertheless, this study brought results consistent with our assumptions at the guild level, indicating that different species of a guild favour similar foraging strategies. In winter, female parasitoids generally adopted an opportunistic strategy, accepting all aphid hosts encountered, even if they were suboptimal. In spring, parasitoids displayed a specialist strategy by selecting preferentially a host species, but the better quality of preferentially selected species remains to be fully demonstrated.

Unravelling the role of host plant expansion in the diversification of a Neotropical butterfly genus.

BackgroundUnderstanding the processes underlying diversification is a central question in evolutionary biology. For butterflies, access to new host plants provides opportunities for adaptive speciation. On the one hand, locally abundant host species can generate ecologically significant selection pressure. But a diversity of host plant species within the geographic range of each population and/or species might also eliminate any advantage conferred by specialization. This paper focuses on four Melinaea species, which are oligophagous on the family Solanaceae: M. menophilus, M. satevis, M. marsaeus, and finally, M. mothone. We examined both female preference and larval performance on two host plant species that commonly occur in this butterfly’s native range, Juanulloa parasitica and Trianaea speciosa, to determine whether the different Melinaea species show evidence of local adaptation.ResultIn choice experiments, M. mothone females used both host plants for oviposition, whereas all other species used J. parasitica almost exclusively. In no choice experiment, M. mothone was the only species that readily accepted T. speciosa as a larval host plant. Larval survival was highest on J. parasitica (82.0 % vs. 60.9 %) and development took longer on T. speciosa (14.12 days vs. 13.35 days), except for M. mothone, which did equally well on both host plants. For all species, average pupal weight was highest on J. parasitica (450.66 mg vs. 420.01 mg), although this difference was least apparent in M. mothone.ConclusionWe did not find that coexisting species of Melinaea partition host plant resources as expected if speciation is primarily driven by host plant divergence. Although M. mothone shows evidence of local adaptation to a novel host plant, T. speciosa, which co-occurs, it does not preferentially lay more eggs on or perform better on this host plant than on host plants used by other Melinaea species and not present in its distributional range. It is likely that diversification in this genus is driven by co-occurring Müllerian mimics and the resulting predation pressure, although this is also likely made possible by greater niche diversity as a consequence of plasticity for potential hosts.

Relative fitness of a generalist parasite on two alternative hosts: a cross‐infestation experiment to test host specialization of the hen flea Ceratophyllus gallinae (Schrank)

Host range is a key element of a parasite's ecology and evolution and can vary greatly depending on spatial scale. Generalist parasites frequently show local population structure in relation to alternative sympatric hosts (i.e. host races) and may thus be specialists at local scales. Here, we investigated local population specialization of a common avian nest-based parasite, the hen flea Ceratophyllus gallinae (Schrank), exploiting two abundant host species that share the same breeding sites, the great tit Parus major (Linnaeus) and the collared flycatcher Ficedula albicollis (Temminck). We performed a cross-infestation experiment of fleas between the two host species in two distinct study areas during a single breeding season and recorded the reproductive success of both hosts and parasites. In the following year, hosts were monitored again to assess the long-term impact of cross-infestation. Our results partly support the local specialization hypothesis: in great tit nests, tit fleas caused higher damage to their hosts than flycatcher fleas, and in collared flycatcher nests, flycatcher fleas had a faster larval development rates than tit fleas. However, these results were significant in only one of the two studied areas, suggesting that the location and history of the host population can modulate the specialization process. Caution is therefore called for when interpreting single location studies. More generally, our results emphasize the need to explicitly account for host diversity in order to understand the population ecology and evolutionary trajectory of generalist parasites.

An introduced parasitic fly may lead to local extinction of Darwin's finch populations.

Introduced pathogens and other parasites are often implicated in host population level declines and extinctions. However, such claims are rarely supported by rigorous real-time data. Indeed, the threat of introduced parasites often goes unnoticed until after host populations have declined severely. The recent introduction of the parasitic nest fly, Philornis downsi, to the Galápagos Islands provides an opportunity to monitor the current impact of an invasive parasite on endemic land bird populations, including Darwin's finches.In this paper we present a population viability model to explore the potential long-term effect of P. downsi on Darwin's finch populations. The goal of our study was to determine whether P. downsi has the potential to drive host populations to extinction and whether management efforts are likely to be effective.Our model is based on data from five years of experimental field work documenting the effect of P. downsi on the reproductive success of medium ground finch Geospiza fortis populations on Santa Cruz Island. Under two of the three scenarios tested, the model predicted medium ground finches are at risk of extinction within the next century.However, sensitivity analyses reveal that even a modest reduction in the prevalence of the parasite could improve the stability of finch populations. We discuss the practicality of several management options aimed at achieving this goal.Synthesis and applications. Our study demonstrates the predicted high risk of local extinction of an abundant host species, the medium ground finch Geospiza fortis due to an introduced parasite, Philornis downsi. However, our study further suggests that careful management practices aimed at reducing parasite prevalence have the potential to significantly lower the risk of host species extinction.

The effect of soil-borne pathogens depends on the abundance of host tree species.

The overarching issue for understanding biodiversity maintenance is how fitness advantages accrue to a species as it becomes rare, as this is the defining feature of stable coexistence mechanisms. Without these fitness advantages, average fitness differences between species will lead to exclusion. However, empirical evidence is lacking, especially for forests, due to the difficulty of manipulating density on a large-enough scale. Here we took advantage of naturally occurring contrasts in abundance between sites of a subtropical tree species, Ormosia glaberrima, to demonstrate how low-density fitness advantages accrue by the Janzen–Connell mechanism. The results showed that soil pathogens suppressed seedling recruitment of O. glaberrima when it is abundant but had little effect on the seedlings when it is at low density due to the lack of pathogens. The difference in seedling survival between abundant and low-density sites demonstrates strong dependence of pathogenic effect on the abundance of host species.

The genome of the vervet (Chlorocebus aethiops sabaeus).

We describe a genome reference of the African green monkey or vervet (Chlorocebus aethiops). This member of the Old World monkey (OWM) superfamily is uniquely valuable for genetic investigations of simian immunodeficiency virus (SIV), for which it is the most abundant natural host species, and of a wide range of health-related phenotypes assessed in Caribbean vervets (C. a. sabaeus), whose numbers have expanded dramatically since Europeans introduced small numbers of their ancestors from West Africa during the colonial era. We use the reference to characterize the genomic relationship between vervets and other primates, the intra-generic phylogeny of vervet subspecies, and genome-wide structural variations of a pedigreed C. a. sabaeus population. Through comparative analyses with human and rhesus macaque, we characterize at high resolution the unique chromosomal fission events that differentiate the vervets and their close relatives from most other catarrhine primates, in whom karyotype is highly conserved. We also provide a summary of transposable elements and contrast these with the rhesus macaque and human. Analysis of sequenced genomes representing each of the main vervet subspecies supports previously hypothesized relationships between these populations, which range across most of sub-Saharan Africa, while uncovering high levels of genetic diversity within each. Sequence-based analyses of major histocompatibility complex (MHC) polymorphisms reveal extremely low diversity in Caribbean C. a. sabaeus vervets, compared to vervets from putatively ancestral West African regions. In the C. a. sabaeus research population, we discover the first structural variations that are, in some cases, predicted to have a deleterious effect; future studies will determine the phenotypic impact of these variations.

Insect herbivory in alpine grasslands is constrained by community and host traits

AbstractQuestionThe consumption of plant biomass by herbivores is an important biotic interaction with possible cascading effects from the level of individual plant performance up to ecosystem functions. However, little is known about the degree and patterns of insect herbivory in alpine ecosystems. We searched for altitudinal differences in herbivory and tested for effects of traits of both the host plants and the surrounding plant communities on herbivory incidence to evaluate predictions derived from the resource availability and the resource concentration hypothesis.LocationHigh‐altitude grasslands of the eastern European Alps.MethodsWe recorded insect herbivory on leaves of five plant taxa differing in traits related to nutritional value and anti‐herbivore resistance to provide the first large‐scale assessment of herbivory in high‐altitude environments. Regression analyses were used to test for significant effects of plant community diversity, host species abundance and soil fertility at grasslands in the lower and upper alpine belt.ResultsWe found a positive correlation of the incidence of folivory with local plant species richness, soil fertility and local host species abundance. The effects of community traits were stronger at higher altitudes, although the overall level of herbivory was lower at higher altitudes. Taxa lacking strong chemical defences, but possessing either high nutrient or high silica content, were particularly strongly and weakly affected by herbivory, respectively.ConclusionsThese results are in line with predictions derived from the resource availability hypothesis, but remain ambiguous concerning the resource concentration hypothesis. The degree of herbivory not only depends on traits of hosts but also on features of the surrounding plant community. The generally high incidence of herbivory with low levels of damage suggests that insect folivores are omnipresent in high‐altitude grasslands.

Fleas of small mammals on Reunion Island: diversity, distribution and epidemiological consequences.

The diversity and geographical distribution of fleas parasitizing small mammals have been poorly investigated on Indian Ocean islands with the exception of Madagascar where endemic plague has stimulated extensive research on these arthropod vectors. In the context of an emerging flea-borne murine typhus outbreak that occurred recently in Reunion Island, we explored fleas' diversity, distribution and host specificity on Reunion Island. Small mammal hosts belonging to five introduced species were trapped from November 2012 to November 2013 along two altitudinal transects, one on the windward eastern and one on the leeward western sides of the island. A total of 960 animals were trapped, and 286 fleas were morphologically and molecularly identified. Four species were reported: (i) two cosmopolitan Xenopsylla species which appeared by far as the prominent species, X. cheopis and X. brasiliensis; (ii) fewer fleas belonging to Echidnophaga gallinacea and Leptopsylla segnis. Rattus rattus was found to be the most abundant host species in our sample, and also the most parasitized host, predominantly by X. cheopis. A marked decrease in flea abundance was observed during the cool-dry season, which indicates seasonal fluctuation in infestation. Importantly, our data reveal that flea abundance was strongly biased on the island, with 81% of all collected fleas coming from the western dry side and no Xenopsylla flea collected on almost four hundred rodents trapped along the windward humid eastern side. The possible consequences of this sharp spatio-temporal pattern are discussed in terms of flea-borne disease risks in Reunion Island, particularly with regard to plague and the currently emerging murine typhus outbreak.

Non-random biodiversity loss underlies predictable increases in viral disease prevalence

Disease dilution (reduced disease prevalence with increasing biodiversity) has been described for many different pathogens. Although the mechanisms causing this phenomenon remain unclear, the disassembly of communities to predictable subsets of species, which can be caused by changing climate, land use or invasive species, underlies one important hypothesis. In this case, infection prevalence could reflect the competence of the remaining hosts. To test this hypothesis, we measured local host species abundance and prevalence of four generalist aphid-vectored pathogens (barley and cereal yellow dwarf viruses) in a ubiquitous annual grass host at 10 sites spanning 2000 km along the North American West Coast. In laboratory and field trials, we measured viral infection as well as aphid fecundity and feeding preference on several host species. Virus prevalence increased as local host richness declined. Community disassembly was non-random: ubiquitous hosts dominating species-poor assemblages were among the most competent for vector production and virus transmission. This suggests that non-random biodiversity loss led to increased virus prevalence. Because diversity loss is occurring globally in response to anthropogenic changes, such work can inform medical, agricultural and veterinary disease research by providing insights into the dynamics of pathogens nested within a complex web of environmental forces.

A walk on the tundra: Host-parasite interactions in an extreme environment.

Climate change is occurring very rapidly in the Arctic, and the processes that have taken millions of years to evolve in this very extreme environment are now changing on timescales as short as decades. These changes are dramatic, subtle and non-linear. In this article, we discuss the evolving insights into host-parasite interactions for wild ungulate species, specifically, muskoxen and caribou, in the North American Arctic. These interactions occur in an environment that is characterized by extremes in temperature, high seasonality, and low host species abundance and diversity. We believe that lessons learned in this system can guide wildlife management and conservation throughout the Arctic, and can also be generalized to more broadly understand host-parasite interactions elsewhere. We specifically examine the impacts of climate change on host-parasite interactions and focus on: (I) the direct temperature effects on parasites; (II) the importance of considering the intricacies of host and parasite ecology for anticipating climate change impacts; and (III) the effect of shifting ecological barriers and corridors. Insights gained from studying the history and ecology of host-parasite systems in the Arctic will be central to understanding the role that climate change is playing in these more complex systems.

A hypothesis to explain host species differences in resistance to multi-host parasites

Here, we offer a novel hypothesis to explain why some host species evolve resistance, whereas other related species remain susceptible to a shared parasite species. We first describe instances of single water mite species that are ectoparasitic on different species of host dragonflies, where the mites are killed by resistance mechanisms and have little to no fitness on some host species. This begs the question of why some host species are susceptible, whereas other host species are (nearly) completely resistant. Earlier logic based on parasites exploiting abundant host species at the cost of exploiting rare host species does not explain such instances well. Rather, a hypothesis based on closed populations of some host species being able to evolve parasite recognition is invoked. Parasite recognition is not expected to evolve in host species from more open populations with considerable gene flow across sites, only some sites of which have the parasite species present. The logic of this hypothesis can be explored with simulation models, whereas empirical tests could involve combined approaches using molecular genetics, population genetics, experimental infections and transplantation experiments.

Assessing the influence of geography, land cover and host species on the local abundance of a generalist brood parasite, the brown‐headed cowbird

AbstractAimThe brown‐headed cowbird is an obligate brood parasite known to exploit a large number of host species and use a variety of habitats. Much attention has been directed towards uncovering the fundamental factors that affect cowbird abundance; however, no study has evaluated these factors in the context of a biogeographic‐scale analysis that takes into account spatial autocorrelation. Our primary objective was to compare the relative influence of geography, land cover and host species on the local abundance of cowbirds.LocationGreat Plains region of the USA.MethodsWe used data from the North American Breeding Bird Survey and the National Land Cover Database to examine the relationships between cowbird abundance and host species, land cover composition and geographic location of a survey route. Multiple regression models were developed for various combinations of these factors. To control for spatial autocorrelation, we used SAM 4.0 (Spatial Analysis in Macroecology) software to implement simultaneous autoregressive modelling of the error term. We then used a model comparison approach to identify the factors that most influence cowbird abundance.ResultsAmong all models examined, host species richness was the single most strong predictor and the sole statistically significant predictor. Cowbird abundance increased with host species richness but did not change in any significant way with non‐host passerine richness or abundance of host species. Models with land cover variables tended to have the poorest fit to the cowbird abundance data.Main conclusionsOur results suggest that cowbirds may be attracted to areas with greater host richness and/or recruit better in such areas, although our data did not allow direct examination of either process. In a greater context, our study demonstrates the utility of a spatially based and geographically extensive analysis in finding range‐wide factors that affect the local abundance of a species.