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Local extinction of the Asian tiger mosquito ( Aedes albopictus ) following rat eradication on Palmyra Atoll

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The Asian tiger mosquito,Aedes albopictus,appears to have been extirpated from Palmyra Atoll following rat eradication. Anecdotal biting reports, collection records, and regular captures in black-light traps showed the species was present before rat eradication. Since then, there have been no biting reports and no captures over 2 years of extensive trapping (black-light and scent traps). By contrast, the southern house mosquito,Culex quinquefasciatus,was abundant before and after rat eradication. We hypothesize that mammals were a substantial and preferred blood meal forAedes, whereasCulexfeeds mostly on seabirds. Therefore, after rat eradication, humans and seabirds alone could not support positive population growth or maintenance ofAedesThis seems to be the first documented accidental secondary extinction of a mosquito. Furthermore, it suggests that preferred host abundance can limit mosquito populations, opening new directions for controlling important disease vectors that depend on introduced species like rats.
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Research
Cite this article: Lafferty KD et al. 2018 Local
extinction of the Asian tiger mosquito (Aedes
albopictus) following rat eradication on
Palmyra Atoll. Biol. Lett. 14: 20170743.
http://dx.doi.org/10.1098/rsbl.2017.0743
Received: 5 December 2017
Accepted: 1 February 2018
Subject Areas:
ecology, environmental science, health and
disease and epidemiology
Keywords:
secondary extinction, extirpation, Rattus,Culex
Author for correspondence:
Kevin D. Lafferty
e-mail: lafferty@lifesci.ucsb.edu
Electronic supplementary material is available
online at https://dx.doi.org/10.6084/m9.
figshare.c.4007599.
Conservation biology
Local extinction of the Asian tiger
mosquito (Aedes albopictus) following
rat eradication on Palmyra Atoll
Kevin D. Lafferty1,2, John P. McLaughlin3, Daniel S. Gruner4, Taylor A. Bogar3,
An Bui3, Jasmine N. Childress3, Magaly Espinoza3, Elizabeth S. Forbes3,
Cora A. Johnston2,4, Maggie Klope3, Ana Miller-ter Kuile3, Michelle Lee3,
Katherine A. Plummer5, David A. Weber5, Ronald T. Young3
and Hillary S. Young3
1
Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA
2
Marine Science Institute, and
3
Department of Ecology Evolution and Marine Biology, University of California
Santa Barbara, Santa Barbara, CA 93106, USA
4
Department of Entomology, University of Maryland, College Park, MD 20742, USA
5
Department of Biology, Stanford University, Standford, CA 94305, USA
KDL, 0000-0001-7583-4593; DSG, 0000-0002-3153-4297; HSY, 0000-0003-0449-8582
The Asian tiger mosquito, Aedes albopictus, appears to have been extirpated
from Palmyra Atoll following rat eradication. Anecdotal biting reports, collec-
tion records, and regular captures in black-light traps showed the species was
present before rat eradication. Since then, there have been no biting reports
and no captures over 2 years of extensive trapping (black-light and scent
traps). By contrast, the southern house mosquito, Culex quinquefasciatus,
was abundant before and after rat eradication. We hypothesize that mam-
mals were a substantial and preferred blood meal for Aedes, whereas Culex
feeds mostly on seabirds. Therefore, after rat eradication, humans and sea-
birds alone could not support positive population growth or maintenance
of Aedes. This seems to be the first documented accidental secondary extinc-
tion of a mosquito. Furthermore, it suggests that preferred host abundance
can limit mosquito populations, opening new directions for controlling
important disease vectors that depend on introduced species like rats.
1. Background
Introduced rats threaten native species (like seabirds), cause economic damage,
and can transmit diseases to humans [1]. In response, humans invest billions of
dollars in rat control. However, rat eradications have not been linked to mos-
quito extirpations. This is consistent with the assumption that blood-feeding
success does not limit mosquitoes [2]. Under such assumptions, rat declines
should increase mosquito bites on humans owing to vector switching (elec-
tronic supplementary material). However, because egg laying typically
requires a blood meal, it makes sense that mosquito abundance, and perhaps
persistence, would depend on blood-feeding success, which itself should
increase with host density and suitability [3]. If so, removing preferred hosts
such as rats could drive mosquitoes to secondary extinction, thereby reducing
bites on humans [4,5] (electronic supplementary material).
Palmyra Atoll has no native mosquitoes, but its wet tropical climate is suit-
able for the southern house mosquito, Culex quinquefasciatus (hereafter Culex),
&2018 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution
License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original
author and source are credited.
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and the Asian tiger mosquito, Aedes albopictus (hereafter Aedes).
Culex was introduced during World War II [6]; it is small and
bites at night, feeding mostly on birds, but also on mammals,
including humans [7] (figure 1, top-left panel). Through its
bites, this Culex species can vector lymphatic filariasis, West
Nile fever and Japanese encephalitis. Aedes arrived sometime
before 2002, when Chris Depkin collected larvae and adults
(Bishop Museum accession no. 2018.003). Adult females are
large, aggressive day-time biters, with conspicuous striped
coloration, preferring mammals, including rats [7], but some
Aedes populations will feed on birds when mammals are not
available [7] (figure 1, bottom-left panel). This Aedes species
can vector lymphatic filariasis, yellow fever, Rift Valley fever,
dengue fever, chikungunya and Zika [8]. Although there
have been no documented vectored diseases on Palmyra,
both mosquitoes were a nuisance.
In June 2011, the approximately 40 000 rats on Palmyra
were eradicated by applying brodifacoum [9]. After rat eradi-
cation, rat prey, like palm seedlings and crabs, increased [10].
Although mosquitoes still harassed people in the evenings,
visitors found it unnecessary to apply mosquito repellent
during the day and began to suspect Aedes had been
extirpated.
2. Material and methods
Palmyra Atoll National Wildlife Refuge (58520N, 1628040W)
lacks an indigenous human population. The atoll has a saltwater
lagoon encircled by two-dozen natural and created islets covered
by introduced coconuts or tall native trees and shrubs. Breeding
seabirds nest in the native forests, whereas shorebirds use the
flats and shoreline. Although there are no native mammals and
few native insects [11], humans (especially a US military occu-
pation in World War II) have introduced rats and many plant
and insect species.
In 2009, before rat eradication, we surveyed flying insects
with black-light traps (John Hock, New Standard Miniature
BlackLight (UV) Trap Model 1212, unbaited, no CO
2
) across 15
islets during 54 nights (electronic supplementary material). All
traps were hung 1– 2 m above ground level, 1– 2 h before dusk
and collected 2 3 h after dawn (details in [12]).
After rat eradication, we (i) surveyed researchers about when
and how often they were bitten by mosquitoes (see electronic sup-
plementary material), (ii) intensified mosquito survey efforts, and
(iii) modified a model [5] describing conditions for mosquito extir-
pation (electronic supplementary material). We completed 53
trap-nights across 25 islets in 2015 and 80 trap-nights across 24
islets in 2016 (see electronic supplementary material). We also con-
ducted a year-long mosquito-monitoring programme near the
main camp on Cooper Island. From 7 December 2015 to 7
August 2017, we hung a black-light trap in the forest, 100 m
from camp. This trap was deployed overnight, once a week
(during dry weather) 54 times over 20 months. We also used
scent traps after rat eradication, because these are more effective
than black-light traps for sampling Aedes [13]. Scent traps were
hung in high human-use areas for eight continuous months (7 Jan-
uary 2015 to 27 June 2015, replacing scent on 22 March 2015).
Then, in July and August 2015 we hung a scent trap for 72 h on
the three islands where Aedes were detected by black-light trap
in 2009.
We compared each mosquito species captured per trap-night
before and after eradication using a general linear mixed model
with island as a random effect (using the square-root transform-
ation on mosquito count to help meet normality assumptions,
though we present the untransformed means below). We also
birds
n = 5000–500 000
n.s.
humans
n = 5–30
rats
n = 40 000
0
Culex quinquefasciatus
Aedes albopictus
20
10
0
0.2
0.1
0
before after
*
mosquitoes per night (black-light)
Figure 1. Aedes, primarily a mammal feeder, likely lost its main blood meal after rat eradication, leading to its coextinction. In contrast, Culex uses seabirds and shorebirds
as preferred hosts and was less impacted by rat eradication (bars show means and s.e.). Solid lines indicate primary hosts; dashed lines indicate incidental hosts. (Online
version in colour.)
rsbl.royalsocietypublishing.org Biol. Lett. 14: 20170743
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calculated the pooled proportional abundance of species trapped
(i.e. Aedes/(Culex þAedes)), allowing us to estimate percentage of
Aedes (+95% CI, binomial exact method) before and after rat
eradication.
3. Results
In 2009, before rat eradication, Aedes (0.03 +0.40 s.e. per trap
set) were present, but less abundant per black-light trap-night
than were Culex (2.46 +0.40 s.e.) ( p,0.0001, figure 1, right
panel), though, because Aedes are less likely to be captured
by black-light traps [13], this does not imply that Aedes
were less abundant than Culex. Pooling counts per mosquito
species across traps suggested that Aedes composed 5.9%
(2.6%11.3%, 95% CI) of the mosquito individuals in black-
light traps before rat eradication. A simple model suggests
that Aedes could persist on a dense rat population (e.g. the
approximately 40 000 rats present in 2009) or a dense
human population (e.g. the 2400 military personnel in
World War II), but not under current conditions with no
rats and 5– 30 humans ( figure 2).
After rat eradication, researchers were bitten less often,
and almost always at night (electronic supplementary
material). The increased sampling effort captured 35-fold
more mosquitoes than before rat eradication (electronic sup-
plementary material). There was no significant difference in
Culex caught per trap-night before (2.7 +5.5 s.e.) than after
(10.6 +4.7 s.e.) rat eradication ( p¼0.69). However, the zero
Aedes caught per black-light trap-night after (0 +0.047 s.e.)
was significantly less than before (0.15+0.052 s.e.) rat eradi-
cation ( p¼0.0004, figure 1, bottom-right panel). In the
pooled samples, Aedes composed none (0.00% 0.22%, 95%
CI) of the mosquitoes in black-light traps. Pooling the more
sensitive scent trap data gave us more confidence that Aedes
composed none (0.00%0.12%, 95% CI) of the mosquitoes
after rat eradication.
In summary, Culex persisted after rat eradication, while
Aedes went from being present even in non-targeted trapping
efforts before rat eradication to undetectable after rat eradica-
tion, despite much greater, and more targeted trapping effort
(table 1).
4. Discussion
Had rat densities simply been reduced rather than eradicated,
or had human densities been higher after rat eradication,
biting rates on humans could have increased as mosquitoes
switched from rats to humans (see figure in electronic sup-
plementary material). Instead, bites from Aedes ceased. Our
inability to document an Aedes bite, or trap an Aedes mos-
quito, over 2 years of sensitive surveillance meets the World
Health Organization’s standards for demonstrating mosquito
eradication [8]. Most mosquito eradications are fleeting,
because mosquitoes can soon recolonize. For instance,
cycles of Aedes eradication and reintroduction followed inten-
sive spraying on Kwajalein Island [14]. The Palmyra
eradication seems different: lack of recovery over 6 years
suggests that conditions on Palmyra have become unsuitable
for Aedes.
mosquito density
2400 people
30 people
200 000
150 000
100 000
50 000
0 500 1000 1500 2000 2500 3000
rat density
log ESL
ESL + SA –1 BHH
BN
Figure 2. Modelled relationship between Aedes density and host densities predicts that Aedes should not persist without rats and with few humans (electronic
supplementary material). (Online version in colour.)
Table 1. Relative mosquito abundance, by species, before (2009) and after
(2015 2016) rat eradication (2011) using black-light traps, scent traps and
biting observations. n.a., not available.
species method sensitivity rats no. rats
Culex black-light moderate common common
Culex scent moderate n.a. common
Culex anecdotal highest common common
Aedes black-light low uncommon absent
Aedes scent high n.a. absent
Aedes anecdotal highest common absent
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We hypothesize that Aedes was eradicated from Palmyra
primarily because its persistence depended on taking blood
meals from rats (figure 1). Rat eradication could have also
reduced larval habitat because rats open coconut husks,
creating suitable habitat for container-breeders like Aedes
and Culex [15]. Larval habitat might have also declined
after the 2011 rat eradication, because 2011 and 2012 were
drier than average years. However, rainfall records since
2002 indicate both wetter and dryer than average years
before and after rat eradication, with no prolonged droughts
(see electronic supplementary material), suggesting that such
dry periods would not have eradicated Aedes on their own.
Therefore, we expect this Aedes eradication will last as long
as rats fail to re-invade Palmyra.
Although there are few documented coextinctions [16],
examples include 10 parasitic trematode species that went
locally extinct after their snail host was extirpated [17], a rat
tick that went extinct along with the Christmas Island rat
[18], and 11 bird lice species extirpated when their island-
endemic bird hosts went extinct [19]. In fact, Aedes is not
the only putative secondary extinction associated with the
Palmyra rat eradication. Most rats on Palmyra were parasi-
tized with a rodent-specific stomach nematode [20], which
must have also gone extinct on the atoll after rat eradication.
These changes in the Palmyra food web show how removing
introduced rats can have unintended indirect effects, including
eradicating an introduced disease vector.
Ethics. All work undertaken with ethical approval of the Palmyra Atoll
National Wildlife Refuge. Survey done under UCSB human subjects
protocol 2-17-1019.
Data accessibility. Datasets have been uploaded as electronic supplemen-
tary material.
Authors’ contributions. K.D.L., J.P.M., D.S.G., and H.S.Y. designed
research and wrote the paper. J.P.M., T.A.B., A.B., J.N.C., M.E.,
E.S.F., C.A.J., M.K., A.M.K., M.L., K.A.P., D.A.W., R.T.Y. and H.S.Y.
acquired data. All authors helped draft the manuscript, approved
the final version, and agreed to be held accountable for the content
therein.
Competing interests. We declare we have no competing interests.
Funding. This study was funded by NSF DEB award no. 1457371 to
H.S.Y. and K.D.L.
Acknowledgements. We thank Palmyra Atoll National Wildlife Refuge,
US Fish and Wildlife Service, Department of the Interior, the
Bishop Museum, the Nature Conservancy and Ken Keenan, Perri
Barbour, Rex Tercek, Johanna Fornberg and Ana Sofia Guerra for
their assistance. This is contribution PARC-141. Any use of trade,
product or firm names in this publication is for descriptive purposes
only and does not imply endorsement by the US Government.
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... A recent major rat poisoning effort (chemical) eliminated the rats entirely. When follow up visits were conducted to check on recovery of endemic species, it became evident (Lafferty et al. 2018; Williams 2018) that the previously introduced Aedes albopictus mosquitoes vanished along with the rats. Researchers speculated that absence of coconut half-shells that once littered the islets as remnants of rat feeding deprived the mosquitoes of freshwater breeding sites. ...
Chapter
In this chapter, we acknowledge the slow development of modern biotechnology in Ecuador. Some research projects have used molecular tools mainly to study the genetic diversity of several plant and animal species of importance for conservation or agriculture. To our knowledge, there could be a few cases, or none at all, in which the use of modern biotechnology is applied for industrial purposes. In this context, we describe an example of a research project related to the genetic transformation of bananas, an important agricultural crop for the country. The current regulations related to this subject are analyzed, and the lack of a National Biosafety Framework that ensures the development and proper use of these technologies in Ecuador is highlighted. The lack of political decision and the correct understanding of modern biotechnology and its implications for various sectors of society represent the greatest challenges that Ecuador has to face in order to be able to handle this issue adequately, promote the development of this type of biotechnology, and preserve the country’s biodiversity.
... As for vectors, if they exclusively depend on primary NHPs for the source of bloodmeal, their survival becomes perilous when mortalities of infected NHPs are high, as in the Americas. In an experiment conducted in an atoll in the Pacific, when all vertebrates were eradicated, the established population of Ae. albopictus became extinct [229]. After all, female vectors can ill afford to discriminate immune from non-immune hosts for survival of the offsprings. ...
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Since the recent epidemics of yellow fever in Angola and Brazil as well as the importation of cases to China in 2016, there has been an increased interest in the century-old enigma, absence of yellow fever in Asia. Although this topic has been repeatedly reviewed before, the history of human intervention has never been considered a critical factor. A two-stage literature search online for this review, however, yielded a rich history indispensable for the debate over this medical enigma. As we combat the pandemic of COVID-19 coronavirus worldwide today, we can learn invaluable lessons from the historical events in Asia. In this review, I explore the history first and then critically examine in depth major hypotheses proposed in light of accumulated data, global dispersal of the principal vector, patterns of YF transmission, persistence of urban transmission, and the possibility of YF in Asia. Through this process of re-examination of the current knowledge, the subjects for research that should be conducted are identified. This review also reveals the importance of holistic approach incorporating ecological and human factors for many unresolved subjects, such as the enigma of YF absence in Asia, vector competence, vector dispersal, spillback, viral persistence and transmission mechanisms.
... cies. for example, the extermination of a rat species from palmyra atoll by poisoning had the unintended, but positive, side effect of also eradicating the tiger mosquito. 181 and on a caribbean island where invasive rats and goats have been eradicated, several salamander species are now going through a more rapid phase of evolution. 182 ...
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This report describes the scientific developments and policy implications of genome editing in animals. Genome editing techniques such as CRISPR-Cas can be used to make small or large changes at specific locations in the DNA of animals with ease and efficiency. Potential applications are in farm animals, pets and laboratory animals as well as in medicine (xenotransplantation) and population control (gene drives in insects and animals in the wild, and even bringing back extinct animal species).
... In addition to seabirds, conservation benefit examples include sea turtles through reduced predation on eggs and hatchlings (Caut et al. 2008;Gronwald et al. 2019) and even indirect effects such as enhancement of coral reef productivity due to increased effects on nutrient cycling through seabird populations (Graham et al. 2018). Eradication of invasive rats on Palmyra Atoll led to another, surprising indirect effect as another invasive species, the disease vectoring Asian tiger mosquito (Aedes albopictus), also disappeared following rat removal (Lafferty et al. 2018). Economic impacts can also be very significant as invasive rodents can destroy crops both in the field and storage (Brown and Singleton 2000). ...
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Since the 1960s conservation efforts have focused on recovering island biodiversity by eradicat- ing invasive rodents. These eradication campaigns have led to considerable conservation gains, particu- larly for nesting seabirds. However, eradications are complex and lengthy endeavors and are even more challenging when humans are co-inhabitants of the targeted island. Furthermore, the method of eradica- tion matters and recent proposals to consider genetic technologies for rodent eradication require specific scrutiny. One such technology is the potential use of a gene drive for biasing offspring sex ratios in invasive house mice, Mus musculus, that would spread and prevent the production of one sex, allowing die-off from lack of reproduction and natural attrition. Practitioners can gain insight into the potential for adoption of this technology from examining stake- holder engagement. This paper uses scenario analysis to address the eradication of rodents on inhabited and uninhabited islands, by specifically comparing the traditional approach of using rodenticides with sex- biasing gene drives. Concurrently the International Union for Conservation of Nature is assessing the risks and value of gene drives in general for conservation. Hence, we make the case that the ethical challenges with the use of gene drive sex-biasing techniques and the effectiveness of this tool will rely as much on its public acceptance and its democratic use as the actual science used to construct the technology.
Chapter
For many years we knew little about microbes because there was no reliable method to identify them. Advances in molecular genetics changed all that. With modern DNA methods, any life form can be identified. Recent studies have also begun to reveal how critically important microbes are to insect biology. The laboratory of Takema Fukatsu in Japan reported the astonishing result, that if you swap the gut microbes of two closely related stink bugs, the insects switch host plants. Genetic transformation has revolutionized plant breeding. It is now possible to apply that approach to insects in improving the ecologically friendly sterile insect technique. It is fair to say the world is having difficulty accepting these new genetic methods. Interdisciplinary studies are a powerful source of innovation.
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Cambridge Core - Natural Resource Management, Agriculture, Horticulture and forestry - Shepherding Nature - by J. Michael Scott
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Extinctions beget further extinctions when species lose obligate mutualists, predators, prey, or hosts. Here, we develop a conceptual model of species and community attributes affecting secondary extinction likelihood, incorporating mechanisms that buffer organisms against partner loss. Specialized interactors, including ‘cryptic specialists’ with diverse but nonredundant partner assemblages, incur elevated risk. Risk is also higher for species that cannot either evolve new traits following partner loss or obtain novel partners in communities reorganizing under changing environmental conditions. Partner loss occurs alongside other anthropogenic impacts; multiple stressors can circumvent ecological buffers, enhancing secondary extinction risk. Stressors can also offset each other, reducing secondary extinction risk, a hitherto unappreciated phenomenon. This synthesis suggests improved conservation planning tactics and critical directions for research on secondary extinctions.
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Background: Aedes albopictus is an invasive species which continues expanding its geographic range and involvement in mosquito-borne diseases such as chikungunya and dengue. Host selection patterns by invasive mosquitoes are critically important because they increase endemic disease transmission and drive outbreaks of exotic pathogens. Traditionally, Ae. albopictus has been characterized as an opportunistic feeder, primarily feeding on mammalian hosts but occasionally acquiring blood from avian sources as well. However, limited information is available on their feeding patterns in temperate regions of their expanded range. Because of the increasing expansion and abundance of Ae. albopictus and the escalating diagnoses of exotic pathogens in travelers returning from endemic areas, we investigated the host feeding patterns of this species in newly invaded areas to further shed light on its role in disease ecology and assess the public health threat of an exotic arbovirus outbreak. Methodology/principal findings: We identified the vertebrate source of 165 blood meals in Ae. albopictus collected between 2008 and 2011 from urban and suburban areas in northeastern USA. We used a network of Biogents Sentinel traps, which enhance Ae. albopictus capture counts, to conduct our collections of blooded mosquitoes. We also analyzed blooded Culex mosquitoes collected alongside Ae. albopictus in order to examine the composition of the community of blood sources. We found no evidence of bias since as expected Culex blood meals were predominantly from birds (n = 149, 93.7%) with only a small proportion feeding on mammals (n = 10, 6.3%). In contrast, Aedes albopictus fed exclusively on mammalian hosts with over 90% of their blood meals derived from humans (n = 96, 58.2%) and domesticated pets (n = 38, 23.0% cats; and n = 24, 14.6% dogs). Aedes albopictus fed from humans significantly more often in suburban than in urban areas (χ(2), p = 0.004) and cat-derived blood meals were greater in urban habitats (χ(2), p = 0.022). Avian-derived blood meals were not detected in any of the Ae. albopictus tested. Conclusions/significance: The high mammalian affinity of Ae. albopictus suggests that this species will be an efficient vector of mammal- and human-driven zoonoses such as La Crosse, dengue, and chikungunya viruses. The lack of blood meals obtained from birds by Ae. albopictus suggest that this species may have limited exposure to endemic avian zoonoses such as St. Louis encephalitis and West Nile virus, which already circulate in the USA. However, growing populations of Ae. albopictus in major metropolitan urban and suburban centers, make a large autochthonous outbreak of an arbovirus such as chikungunya or dengue viruses a clear and present danger. Given the difficulties of Ae. albopictus suppression, we recommend that public health practitioners and policy makers install proactive measures for the imminent mitigation of an exotic pathogen outbreak.
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AbstrAct: Palmyra Atoll National Wildlife Refuge is a moist Central Pacific atoll that supports one of the best remaining tropical forest ecosystems in the region, including 10 species of breeding seabirds and a robust population of the world's largest terrestrial invertebrate, the coconut crab. Despite these riches, the atoll's ecosystem has been modified by introduced black rats that were inad-vertently brought to Palmyra during WWII. Between June 1 and 30, 2011, a partnership between the U.S. Fish and Wildlife Service, The Nature Conservancy, and Island Conservation successfully implemented a project to remove rats from Palmyra. Independent monitoring of bait application and its environmental effects was undertaken by the USDA. Over the 28-day operation, a team of 41 people from 5 countries utilized 2 helicopters, 10 slingshots, 148 bait stations, and hand spreading to strategically apply 38,561 kg of rodent bait containing the anticoagulant brodifacoum (25 ppm) to Palmyra's 235 hectares of emergent land. Palmyra's challenging eradication environment demanded the development of a novel approach, such as broadcast application rates between 75 and 85 kg/ha and the use of "bolas" to bait coastal forest canopy to minimize bait drift into the marine environment. Initial findings show minimal non-target impacts as a result of the project, and post-eradication monitoring has failed to detect rats. Increased recruitment by at least 2 native tree species has been observed. By removing rats from Palmyra, the partnership aims to safeguard the atoll's indigenous flora and fauna, encourage the reestablishment of extirpated seabird species, and create an ecological refuge for species within the Central Pacific region that are at risk of extinction. �his project is a conservation milestone for the Refuge, and it has established a benchmark �his project is a conservation milestone for the Refuge, and it has established a benchmark for eradication campaigns on other tropical islands.
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Many different drivers, including productivity, ecosystem size, and disturbance, have been considered to explain natural variation in the length of food chains. Much remains unknown about the role of these various drivers in determining food chain length, and particularly about the mechanisms by which they may operate in terrestrial ecosystems, which have quite different ecological constraints than aquatic environments, where most food chain length studies have been thus far conducted. In this study, we tested the relative importance of ecosystem size and productivity in influencing food chain length in a terrestrial setting. We determined that (1) there is no effect of ecosystem size or productive space on food chain length; (2) rather, food chain length increases strongly and linearly with productivity; and (3) the observed changes in food chain length are likely achieved through a combination of changes in predator size, predator behavior, and consumer diversity along gradients in productivity. These results lend new insight into the mechanisms by which productivity can drive changes in food chain length, point to potential for systematic differences in the drivers of food web structure between terrestrial and aquatic systems, and challenge us to consider how ecological context may control the drivers that shape food chain length.
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Palmyra Atoll, in the Line Islands of the equatorial Pacific, supports one of the largest remaining native stands of Pisonia grandis forest in the tropical Pacific Ocean. In 2003, we surveyed terrestrial arthropods to document extant native and introduced species richness, compare these lists with historical records, and assess potential threats to native species and ecosystem integrity. In total, 115 arthropod taxa were collected, bringing the total number of taxa recorded since 1913 to 162. Few native species were collected; most taxa were accidental introductions also recorded from the Hawaiian Islands, the presumed main source of introductions to Palmyra. The overlap with previous historical surveys in 1913 and 1948 was low (<40%), and new species continue to establish, with one species of whitefly reaching pest status between 2003 and 2005. We observed numerous dead or dying large Pisonia grandis, and the green scale Pulvinaria urbicola (Coccidae) was particularly abundant on trees of poor health. Abundant introduced ants, particularly Pheidole megacephala, tended this and other hemipterans feeding on both native and introduced plants. We hypothesize that the Pheidole-Pulvinaria facultative mutualism is causing the decline of Pisonia grandis. Because of the unique properties of Pisonia grandis forest on oceanic atolls, its importance for nesting seabirds, and its alarming global decline, immediate conservation efforts should be directed at controlling introduced Hemiptera and disrupting their mutualisms with nonnative ants on Palmyra Atoll.
Article
Invasive rats have colonized most of the islands of the world, resulting in strong negative impacts on native biodiversity and on ecosystem functions. As prolific omnivores, invasive rats can cause local extirpation of a wide range of native species, with cascading consequences that can reshape communities and ecosystems. Eradication of rats on islands is now becoming a widespread approach to restore ecosystems, and many native island species show strong numerical responses to rat eradication. However, the effect of rat eradication on other consumers can extend beyond direct numerical effects, to changes in behavior, dietary composition, and other ecological parameters. These behavioral and trophic effects may have strong cascading impacts on the ecology of restored ecosystems, but they have rarely been examined. In this study, we explore how rat eradication has affected the trophic ecology of native land crab communities. Using stable isotope analysis of rats and crabs, we demonstrate that the diet or trophic position of most crabs changed subsequent to rat eradication. Combined with the numerical recovery of two carnivorous land crab species (Geograpsus spp.), this led to a dramatic widening of the crab trophic niche following rat eradication. Given the established importance of land crabs in structuring island communities, particularly plants, this suggests an unappreciated mechanism by which rat eradication may alter island ecology. This study also demonstrates the potential for stable isotope analysis as a complementary monitoring tool to traditional techniques, with the potential to provide more nuanced assessments of the community- and ecosystem-wide effects of restoration.
Chapter
This chapter deals with the transmission and maintenance of malaria, paying attention both to the overall dynamics and to the population biology of the infection in human hosts and mosquito vectors. We aim to combine some new work with review and synthesis (and, in some cases, reinterpretation) of existing work.
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Coextinction is a poorly quantified phenomenon, but results of recent modeling suggest high losses to global biodiversity through the loss of dependent species when hosts go extinct. There are critical gaps in coextinction theory, and we outline these in a framework to direct future research toward more accurate estimates of coextinction rates. Specifically, the most critical priorities include acquisition of more accurate host data, including the threat status of host species; acquisition of data on the use of hosts by dependent species across a wide array of localities, habitats, and breadth of both hosts and dependents; development of models that incorporate correlates of nonrandom host and dependent extinctions, such as phylogeny and traits that increase extinction-proneness; and determination of whether dependents are being lost before their hosts and adjusting models accordingly. Without synergistic development of better empirical data and more realistic models to estimate the number of cothreatened species and coextinction rates, the contribution of coextinction to global declines in biodiversity will remain unknown and unmanaged.