Kathleen LoGiudice

COMMUNITY DISASSEMBLY, BIODIVERSITY LOSS, AND THE EROSION OF AN ECOSYSTEM SERVICE

Distinguishing the mechanisms responsible for the relationship between biodiversity and ecosystem services requires knowledge of (1) the functional roles played by individual species and (2) the sequence with which species are added to or lost from communities in nature (i.e., “community assembly” and “community disassembly,” respectively). Rarely, if ever, are both these issues understood with certainty in any given ecosystem. We used an empirically based simulation model to assess the degree to which the sequence of species loss from vertebrate communities influences risk of human exposure to Lyme disease, as measured by the proportion of ticks infected with the etiological agent. Dramatic differences in the shapes of the curves relating vertebrate biodiversity to disease risk (which we consider an ecosystem service) were observed. Randomized sequences of species loss resulted in a decrease in disease risk with reduced biodiversity, a result that is contradicted by both empirical observations and model ...

Hosts as ecological traps for the vector of Lyme disease

Vectors of infectious diseases are generally thought to be regulated by abiotic conditions such as climate or the availability of specific hosts or habitats. In this study we tested whether blacklegged ticks, the vectors of Lyme disease, granulocytic anaplasmosis and babesiosis can be regulated by the species of vertebrate hosts on which they obligately feed. By subjecting field-caught hosts to parasitism by larval blacklegged ticks, we found that some host species (e.g. opossums, squirrels) that are abundantly parasitized in nature kill 83–96% of the ticks that attempt to attach and feed, while other species are more permissive of tick feeding. Given natural tick burdens we document on these hosts, we show that some hosts can kill thousands of ticks per hectare. These results indicate that the abundance of tick vectors can be regulated by the identity of the hosts upon which these vectors feed. By simulating the removal of hosts from intact communities using empirical models, we show that the loss of biodiversity may exacerbate disease risk by increasing both vector numbers and vector infection rates with a zoonotic pathogen.

Estimating Reservoir Competence of Borrelia burgdorferi Hosts: Prevalence and Infectivity, Sensitivity, and Specificity

Abstract Most vector-borne zoonotic pathogens are transmitted among several host species, but different species vary considerably in their importance to pathogen transmission, at least partially because they vary in their propensity to infect feeding vectors. This propensity is often called realized reservoir competence. Realized reservoir competence is the product of 1) the probability the individual host is infected, i.e., infection prevalence, and 2) the probability that if the host is infected, it will transmit the infection to a feeding vector, or infectivity. Prevalence varies in space and time, whereas infectivity may be a property of the host species. Both prevalence and infectivity are ecologically and epidemiologically important, but measuring them simultaneously is difficult. We present a probabilistic model that separately estimates host infection prevalence and infectivity from data on the infection status of vectors collected from individual hosts, data generally used to measure realized reservoir competence. We then consider how imperfect diagnostic tests (i.e., false negatives and positives) influence these probabilities—estimates of prevalence and infectivity are fairly robust to false negatives, but not to false positives. We thus extend the model to estimate the rate of false positives in order to improve estimates of prevalence and infectivity. We illustrate these methods by reanalyzing data from LoGiudice et al. (2003; Proc. Natl. Acad. Sci. U.S.A. 100: 567–571) on the reservoir competence of ten vertebrate hosts of Borrelia burgdorferi, the agent of Lyme disease. We find that these vertebrate hosts vary both in prevalence and infectivity and that both values are highly, positively correlated among species.

Toward a Synthetic View of Extinction: A History Lesson from a North American Rodent

Abstract Although it is recognized that many factors interact to cause extinctions, it is difficult to consider multiple factors when investigating species declines. I conducted a post hoc exploration of the major hypotheses for the decline of the Allegheny woodrat (Neotoma magister), incorporated the historical environmental changes that accompanied and preceded the decline, and considered how these events may have affected the species. What emerges is a complicated picture involving multiple, relatively minor stressors, all attributable to human activities. The temporal pattern of the decline is most coherent when considered from a historical perspective. Among the factors that are likely to have affected Allegheny woodrats are two exotic tree pathogens, a native parasite, the proliferation of human-adapted competitors, and habitat fragmentation. In addition, changes in competitive and predatory regimes appear to have influenced the timing of the collapse. Although the historic record cannot give definitive answers, taking a synthetic, historical–ecological approach can enhance understanding of species declines.

Co-Infection of Blacklegged Ticks with Babesia microti and Borrelia burgdorferi Is Higher than Expected and Acquired from Small Mammal Hosts

Humans in the northeastern and midwestern United States are at increasing risk of acquiring tickborne diseases – not only Lyme disease, but also two emerging diseases, human granulocytic anaplasmosis and human babesiosis. Co-infection with two or more of these pathogens can increase the severity of health impacts. The risk of co-infection is intensified by the ecology of these three diseases because all three pathogens (Borrelia burgdorferi, Anaplasma phagocytophilum, and Babesia microti) are transmitted by the same vector, blacklegged ticks (Ixodes scapularis), and are carried by many of the same reservoir hosts. The risk of exposure to multiple pathogens from a single tick bite and the sources of co-infected ticks are not well understood. In this study, we quantify the risk of co-infection by measuring infection prevalence in 4,368 questing nymphs throughout an endemic region for all three diseases (Dutchess County, NY) to determine if co-infections occur at frequencies other than predicted by independent assortment of pathogens. Further, we identify sources of co-infection by quantifying rates of co-infection on 3,275 larval ticks fed on known hosts. We find significant deviations of levels of co-infection in questing nymphs, most notably 83% more co-infection with Babesia microti and Borrelia burgdorferi than predicted by chance alone. Further, this pattern of increased co-infection was observed in larval ticks that fed on small mammal hosts, but not on meso-mammal, sciurid, or avian hosts. Co-infections involving A. phagocytophilum were less common, and fewer co-infections of A. phagocytophilum and B. microti than predicted by chance were observed in both questing nymphs and larvae fed on small mammals. Medical practitioners should be aware of the elevated risk of B. microti/B. burgdorferi co-infection.

Reservoir Competence of Vertebrate Hosts for Anaplasma phagocytophilum

Fourteen vertebrate species (10 mammals and 4 birds) were assessed for their ability to transmit Anaplasma phagocytophilum, the bacterium that causes human granulocytic anaplasmosis, to uninfected feeding ixodid ticks. Small mammals were most likely to infect ticks but all species assessed were capable of transmitting the bacterium, in contrast to previous findings.

Molting success of Ixodes scapularis varies among individual blood meal hosts and species.

ABSTRACT The blacklegged tick (Ixodes scapularis) is an important vector of emerging human pathogens. It has three blood-feeding stages, as follows: larva, nymph, and adult. Owing to inefficient transovarial transmission, at least for the Lyme disease agent (Borrelia burgdorferi), larval ticks rarely hatch infected, but they can acquire infection during their larval blood meal. Nymphal ticks are primarily responsible for transmitting pathogens to hosts, including humans. The transition from uninfected host-seeking larva to infectious host-seeking nymph is therefore a key aspect of human risk of infection. It can be divided into a series of steps, as follows: finding a host, taking a blood meal, becoming infected, molting, and overwintering. The chance of succeeding in each of these steps may depend on the species identity of the blood meal host. We used a Bayesian method to estimate the molting success of larval I. scapularis collected from four commonly parasitized species of birds and eight commonly parasitized small and mid-sized mammals found in the forests of Dutchess County, New York. We show that molting success varies substantially among host species; white-footed mice, veeries, and gray catbirds support particularly high molting success, whereas ticks feeding on shorttailed shrews, robins, and wood thrushes were less successful. We also show that larval molting success varies substantially between individual blood meal hosts, and that this intraspecific variability is much higher in some species than in others. The causes of both inter- and intraspecific variation in molting success remain to be determined.

Prevalence of human-active and variant 1 strains of the tick-borne pathogen Anaplasma phagocytophilum in hosts and forests of eastern North America.

Anaplasmosis is an emerging infectious disease caused by infection with the bacterium Anaplasma phagocytophilum. In the eastern United States, A. phagocytophilum is transmitted to hosts through the bite of the blacklegged tick, Ixodes scapularis. We determined the realized reservoir competence of 14 species of common vertebrate hosts for ticks by establishing the probability that each species transmits two important strains of A. phagocytophilum (A. phagocytophilum human-active, which causes human cases, and A. phagocytophilum variant 1, which does not) to feeding larval ticks. We also sampled questing nymphal ticks from ∼ 150 sites in a single county over 2 years and sampled over 6 years at one location. White-footed mice (Peromyscus leucopus) and Eastern chipmunks (Tamias striatus) were the most competent reservoirs for infection with the A. phagocytophilum human-active strain. Across the county, prevalence in ticks for both strains together was 8.3%; ticks were more than two times as likely to be infected with A. phagocytophilum human-active as A. phagocytophilum variant 1.

Transforming Ecological Science at Primarily Undergraduate Institutions through Collaborative Networks

Ecologists at primarily undergraduate institutions (PUIs) are well positioned to form collaborative networks and make transformative contributions to the study and teaching of ecology. The spatial and temporal complexity of ecological phenomena rewards a collaborative research approach. A network of PUI ecologists can incorporate closely supervised data collection into undergraduate courses, thereby generating data across spatial gradients to answer crucial questions. These data can offer unprecedented insight into fine- and large-scale spatial processes for publications, resource management, and policy decisions. Undergraduate students benefit from the collaborative research experience as they gain experiential learning in team building, project design, implementation, data collection, and analysis. With appropriate funding, collaborative networks make excellent use of the intellectual and experiential capital of PUI faculty for the benefit of science, pedagogy, and society.

Multiple Causes of the Allegheny Woodrat Decline: A Historical–Ecological Examination

Wandering through the former haunts of the Allegheny woodrat (Neotoma magister) in the Shawangunk Mountains of New York State, one might easily imagine that this landscape is largely unchanged from what it was hundreds of years ago. Massive chestnut oaks (Quercus prinus) protrude from rocky hillsides and steep talus slopes conceal complex systems of fissures and galleries beneath. However, one need not look far to see signs of changing land uses all around this beautiful region. Even in areas seemingly untouched by human hands, the plant and animal communities of northeastern North America have undergone profound changes in the past 400 years—a fact not often considered when pondering the causes for a species’ decline. And yet, a short moment of reflection brings to mind a plethora of important species that no longer exist in our landscape. The American chestnut (Castanea dentata) and the American elm (Ulmus americana) are no longer found in our forests. The eastern hemlock (Tsuga canadensis), American beech (Fagus grandifolia), and eastern dogwood (Cornus florida) are fast disappearing. The list of animal species once found in the northeast but now absent is also quite impressive, including wolves (Canis lupus), cougars (Felis concolor), passenger pigeons (Ectopistes migratorius), wolverines (Gulo gulo), bison (Bison bison), and lynx (Lynx canadensis). Equally noteworthy is the reversal of devastating trends that once appeared unidirectional; deforestation gave way to reforestation which has given way to suburbanization. Some species appear to have disappeared from the northeast forever. Others, like white-tailed deer (Odocoileus virginianus), American turkeys (Meleagris gallopavo), black bears (Ursus americanus), and American beavers (Castor canadensis) declined only to rebound to levels once thought impossible. From a nadir in the 1850s, when Henry David Thoreau noted that the muskrat