SEARCH · Search USGS

Results for “Biology Letters”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources

USGS2010

Strong nonlinear photonic responses from microbiologically synthesized tellurium nanocomposites

A new class of nanomaterials, namely microbiologically-formed nanorods composed of elemental tellurium [Te(0)] that forms unusual nanocomposites when combined with poly(m-phenylenevinylene-co-2,5-dioctoxy-phenylenevinylene) (PmPV) is described. These bio-nanocomposites exhibit excellent broadband optical limiting at 532 and 1064 nm. Nonlinear scattering, originating from the laser induced solvent bubbles and microplasmas, is responsible for this nonlinear behavior. The use of bacterially-formed Te(0) when combined with an organic chemical host (e.g., PmPV) is a new green method of nanoparticle syntheses. This opens the possibilities of using unique, biologically synthesized materials to advance future nanoelectronic and nanophotonic applications.

Chemical Physics Letters↗

USGS2009

Thallium isotope evidence for a permanent increase in marine organic carbon export in the early Eocene

The first high resolution thallium (Tl) isotope records in two ferromanganese crusts (Fe-Mn crusts), CD29 and D11 from the Pacific Ocean are presented. The crusts record pronounced but systematic changes in 205Tl/203Tl that are unlikely to reflect diagenetic overprinting or changes in isotope fractionation between seawater and Fe-Mn crusts. It appears more likely that the Fe-Mn crusts track the Tl isotope composition of seawater over time. The present-day oceanic residence time of Tl is estimated to be about 20,000??yr, such that the isotopic composition should reflect ocean-wide events. New and published Os isotope data are used to construct age models for these crusts that are consistent with each other and significantly different from previous age models. Application of these age models reveals that the Tl isotope composition of seawater changed systematically between ~ 55??Ma and ~ 45??Ma. Using a simple box model it is shown that the present day Tl isotope composition of seawater depends almost exclusively on the ratio between the two principal output fluxes of marine Tl. These fluxes are the rate of removal of Tl from seawater via scavenging by authigenic Fe-Mn oxyhydroxide precipitation and the uptake rate of Tl during low temperature alteration of oceanic crust. It is highly unlikely that the latter has changed greatly. Therefore, assuming that the marine Tl budget has also not changed significantly during the Cenozoic, the low 205Tl/203Tl during the Paleocene is best explained by a more than four-fold higher sequestration of Tl by Fe-Mn oxyhydroxides compared with at the present day. The calculated Cenozoic Tl isotopic seawater curve displays a striking similarity to that of S, providing evidence that both systems may have responded to the same change in the marine environment. A plausible explanation is a marked and permanent increase in organic carbon export from ~ 55??Ma to ~ 45??Ma, which led to higher pyrite burial rates and a significantly reduced flux of Fe-Mn oxide removal as a result of increased biological uptake of Fe and Mn. ?? 2008 Elsevier B.V. All rights reserved.

Earth and Planetary Science Letters↗

USGS1929

A preliminary report on the growth of the rock bass, Ambloplites rupestris (Rafinesque), in two lakes of northern Wisconsin

For several years the Wisconsin Geological and Natural History Survey has been making a limnological study of lakes in the northern part of the State. Because of the fact that so much has been learned of the physical, chemical and biological conditions in these lakes, the region seems particularly favorable for a study of the growth rates of fishes in relation to environmental factors.

Transactions of the Wisconsin Academy of Sciences,↗

USGS1997

A system for monitoring impact of Denali National Park road traffic on wildlife

The Denali National Park and Preserve (DENA) is a 6.03 million acre reserve lying between Anchorage and Fairbanks, Alaska. The park was established in 1917 as a wildlife refuge, and is managed to maintain the wilderness character. With the highest mountain in North America, Mt. McKinley, and the easy availability of wildlife for viewing, the park is Alaska's most favored destination point. From 1972 through 1984, visitation grew from 88, 615 to 394, 426 visitor days per year (GMP, 1986), and then increased by 50,000 per year to 596,000 visitors in 1988. This demand for motorized access to the park, especially along the 92.5 mile-long park road, has resulted in controversy and claims of traffic disturbance to wildlife [(letter from Superintendent, DENA July 13, 1988) (Anchorage Daily News, May 14, 1995; May 26, 1995; February 5, 1996; June 18, 1996) Leo (1987); Lee Rue (1996)].

Biological Science Report↗

USGS2019

Do Indigenous American Peoples’ stories inform the study of dog domestication?

I discuss the article “Relationships Between Indigenous American Peoples and Wolves 1: Wolves as Teachers and Guides” (Fogg et al. 2015) and the book “The First Domestication: How Wolves and Humans Coevolved” (Pierotti and Fogg 2017). The article proposed that published stories about interactions between indigenous American peoples and wolves ( Canis lupus ) provide insight into wolf-human relationships as humans began domesticating wolves. In the book, the authors offer a theory of how wolves and humans coevolved by building on the information in the article and the authors’ long experience with captive and pet wolves, wolf-dog hybrids, and dogs. I (1) present arguments and evidence that question the value of indigenous American stories for drawing conclusions about the relationship between early humans and wolves 14,000 yrs BP; (2) demonstrate how indigenous American stories contradict documented information about wolf biology, behavior, and known interactions with humans; and (3) point out important information not considered by the authors about wolf attacks on humans and the importance of rabies in the wolf-human relationship.

Ethnobiological Letters↗

USGS2023

Deep root activity overprints weathering of petrogenic organic carbon in shale

The oxidation of organic carbon in sedimentary bedrock (petrogenic OC, OC p e t r o "> petro ) is increasingly recognized as a potential source of CO 2 to the atmosphere. Recent studies provide evidence for the mobilization and oxidation of OC p e t r o "> petro in sedimentary bedrock during rock weathering. However, the mechanisms and rates remain uncertain, particularly where overlying soils and vegetation drive contemporaneous oxidation of recently fixed organic carbon. Here, we quantify OC p e t r o "> petro weathering across a 16 m shale depth profile in a steep, rapidly eroding forested hillslope in the Northern California Coast Ranges. We report solid and gas phase radiocarbon and stable isotope analyses of samples extracted from specialized in-situ samplers, and a supporting laboratory incubation experiment of the shale regolith. OC p e t r o "> petro is removed from the weathered bedrock at a rate of approximately 0.12 gC/m 3 yr, which is orders of magnitude lower than the rate of OC p e t r o "> petro oxidation we achieved in the laboratory with crushed samples (557.1 gC/m 3 /yr). This disparity occurs despite high O 2 ( g ) "> 2(g) content across the depth profile, indicating that physical accessibility of OC p e t r o "> petro can regulate oxidative weathering. There is no direct radiocarbon evidence of OC p e t r o "> petro oxidation in CO 2 ( g ) "> 2(g) across the upper 13 m of the weathering profile during both wet and dry seasons. Instead, vadose zone CO 2 ( g ) "> 2(g) production at the site is dominated by respiration of recently fixed carbon associated with deep rooting. OC p e t r o "> petro is clearly mobilized across the vadose zone during weathering in this rapidly eroding, oxygen-rich, biologically dynamic hillslope, but at rates far below what can be measured given the contribution of root-derived CO 2 ( g ) "> 2(g) .

California↗

USGS1993

Volcanic eruption of the mid-ocean ridge along the East Pacific Rise crest at 9°45-52'N: direct submersible observations of seafloor phenomena associated with an eruption event in April, 1991

In April, 1991, we witnessed from the submersible Alvin a suite of previously undocumented seafloor phenomena accompanying an in-progress eruption of the mid-ocean ridge on the East Pacific Rise crest at 9°45′N–52′N. The volume of the eruption could not be precisely determined, although comparison of pre- and post-eruption SeaBeam bathymetry indicate that any changes in ridge crest morphology resulting from the eruption were < 10 m high. Effects of the eruption included: (1) increased abundance and redistribution of hydrothermal vents, disappearance of numerous vent communities, and changes in characteristics of vent fauna and mineral deposits within the eruption area since December, 1989; (2) murkiness of bottom waters up to tens of meters above the seafloor due to high densities of suspended mineral and biogenic particulates; (3) destruction of a vent community by lava flows, mass wasting, and possible hydrovolcanic explosion at a site known as ‘Tubeworm Barbecue’ in the axial summit caldera (ASC) at 9°50.6′N; (4) near-critical temperatures of hydrothermal vent fluids, ranging up to 403°C; (5) temporal variations over a 2 week interval in both temperatures and chemical/isotopic compositions of hydrothermal fluids; (6) unusual compositions of end-member vent fluids, with pH values ranging to a record low of 2.5, salinities ranging as low as 0.3 wt% NaCl (one-twelfth that of seawater), and dissolved gases reaching high concentrations (> 65 mmol/l for both CO 2 and H 2 S); (7) venting at temperatures above 380°C of visually detectable white vapor that transformed to plumes of gray smoke a few centimeters above vent orifices; (8) disorganized venting of both high-temperature fluids (black and gray smoke) and large volumes of cooler, diffuse hydrothermal fluids directly from the basaltic seafloor, rather than from hydrothermal mineral constructions; (9) rapid and extensive growth of flocculent white bacterial mats (species unknown) on and under the seafloor in areas experiencing widespread venting of diffuse hydrothermal fluid; and (10) subseafloor downslope migration of magma normal to the ridge axis in a network of small-scale (1–5 m diameter) lava tubes and channels to distances at least 100–200 m outside the ASC. We suggest that, in April, 1991, intrusion of dikes in the eruption area to < 200 m beneath the ASC floor resulted in phase separation of fluids near the tops of the dikes and a large flux of vapor-rich hydrothermal fluids through the overlying rubbly, cavernous lavas. Low salinities and gas-rich compositions of hydrothermal fluids sampled in the eruption area are appropriate for a vapor phase in a seawater system undergoing subcritical liquid-vapor phase separation (boiling) and phase segregation. Hydrothermal fluids streamed directly from fissures and pits that may have been loci of lava drainback and/or hydrovolcanic explosions. These fissures and pits were lined with white mats of a unique fast-growing bacteria that was the only life associated with the brand-new vents. The prolific bacteria, which covered thousands of square meters on the ridge crest and were also abundant in subseafloor voids, may thrive on high levels of gases in the vapor-rich hydrothermal fluids initially escaping the hydrothermal system. White bacterial particulates swept from the seafloor by hydrothermal vents swirled in an unprecedented biogenic ‘blizzard’ up to 50 m above the bottom. The bacterial proliferation of April, 1991 is likely to be a transient bloom that will be checked quickly either by decline of dissolved gas concentrations in the fluids as rapid heat loss brings about cessation of boiling, and/or by grazing as other organisms are re-established in the biologically devastated area.

Earth and Planetary Science Letters↗

USGS2010

Topographic complexity and roughness of a tropical benthic seascape

Topographic complexity is a fundamental structural property of benthic marine ecosystems that exists across all scales and affects a multitude of processes. Coral reefs are a prime example, for which this complexity has been found to impact water flow, species diversity, nutrient uptake, and wave-energy dissipation, among other properties. Despite its importance, only limited assessments are available regarding the distribution or range of topographic complexity within or between benthic communities. Here, we show substantial variability in topographic complexity over the entire inner-shelf seascape of a tropical island. Roughness, estimated in terms of fractal dimension, served as a proxy for topographic complexity, and was computed for linear transects (D T ), as well as the benthic surface (D S ). Spatial variability in both D T and D S was correlated with the known distribution of benthic cover types in the seascape. Transect roughness values ranged from 1.0 to 1.7, with features along the shelf edge being markedly anisotropic with an along-shore bias, whereas regions with high scleractinian coral cover were nearly isotropic and exhibited minimal directional bias. Surface-roughness values ranged from 2.0 in predominantly hardbottom areas with low coral cover to 2.5 in areas with high coral cover. Quantifying roughness across the substrates and biological communities for an entire seascape provides a synoptic view of its spatial variability at scales appropriate for numerous research efforts, including ecosystem studies, parameterizing hydrodynamic models, and designing monitoring programs.

Geophysical Research Letters↗

USGS1996

Uranium-series disequilibrium, sedimentation, diatom frustules, and paleoclimate change in Lake Baikal

The large volume of water, approximately one-fifth of the total surface fresh water on the planet, contained in Lake Baikal in southeastern Siberia is distinguished by having a relatively high concentration of uranium (ca. 2 n M ), and, together with the surface sediments, an unusually high 234 U 238 U alpha activity ratio of 1.95. About 80% of the input of uranium to the lake, with a 234 U 238 U ratio of 2.0, comes from the Selenga River. Profiles of uranium, as well as the extent of isotopic disequilibrium in a 9 m sediment core collected on Academic Ridge, generally show high values during interglacial periods corresponding to high diatom frustule numbers (DiFr) and biogenic silica (BSi) data that have been reported elsewhere. During glacial periods (low DiFr and BSi), uranium progeny ( 234 U and 230 Th) were in secular equilibrium with low concentrations of their parent 238 U. Radionuclide distributions were interpreted in terms of a quantitative model allowing for adsorption of riverine inputs of uranium onto two classes of sedimenting particles with differing 238 U 232 Th ratios and uranium progeny in secular equilibrium. If the 234 U 238 U activity ratio of adsorbed uranium has remained constant, mean sedimentation rates can be independently estimated as 3.6 ± 0.6 and 3.7 ± 0.9 cm · kyr −1 for the decay of 234 U and in-growth of 230 Th, respectively. These rates are consistent with a mean rate of 3.76 cm · kyr −1 , calculated by optimization of the correspondence between adsorbed 238 U and δ 18 O in dated oceanic sediments. The adsorbed uranium apparently tracks variable river flow during interglacials and is drastically reduced during periods of glaciation. Evidently, uranium has not been significantly redistributed within Baikal sediments over at least the past 250 kyr and is a unique, biologically non-essential, tracer for climate-sensitive processes, which provide their own internal geochronometers, potentially useful for ages up to 1 Myr BP.

Earth and Planetary Science Letters↗

USGS2016

Climate regulates alpine lake ice cover phenology and aquatic ecosystem structure

High-elevation aquatic ecosystems are highly vulnerable to climate change, yet relatively few records are available to characterize shifts in ecosystem structure or their underlying mechanisms. Using a long-term dataset on seven alpine lakes (3126 to 3620 m) in Colorado, USA, we show that ice-off dates have shifted seven days earlier over the past 33 years and that spring weather conditions – especially snowfall – drive yearly variation in ice-off timing. In the most well-studied lake, earlier ice-off associated with increases in water residence times, thermal stratification, ion concentrations, dissolved nitrogen, pH, and chlorophyll-a. Mechanistically, low spring snowfall and warm temperatures reduce summer stream flow (increasing lake residence times) but enhance melting of glacial and permafrost ice (increasing lake solute inputs). The observed links among hydrological, chemical, and biological responses to climate factors highlight the potential for major shifts in the functioning of alpine lakes due to forecasted climate change.

Colorado↗

USGS2005

An astrobiological perspective on Meridiani Planum

Sedimentary rocks exposed in the Meridiani Planum region of Mars record aqueous and eolian deposition in ancient dune and interdune playa-like environments that were arid, acidic, and oxidizing. On Earth, microbial populations have repeatedly adapted to low pH and both episodic and chronic water limitation, suggesting that, to a first approximation, the Meridiani plain may have been habitable during at least part of the interval when deposition and early diagenesis took place. On the other hand, the environmental conditions inferred for Meridiani deposition would have posed a challenge for prebiotic chemical reactions thought to have played a role in the origin of life on Earth. Orbital observations suggest that the combination of sulfate minerals and hematite found in Meridiani rocks may be unusual on the martian surface; however, there is reason to believe that acidity, aridity, and oxidizing conditions were broadly distributed on ancient Mars. When these conditions were established and how much environmental heterogeneity existed on early Mars remain to be determined. Because sulfates and iron oxides can preserve detailed geochemical records of environmental history as well as chemical, textural and microfossil signatures of biological activity, Meridiani Planum is an attractive candidate for Mars sample return. ?? 2005 Elsevier B.V. All rights reserved.

Earth and Planetary Science Letters↗

USGS2006

Vital effects in coral skeletal composition display strict three-dimensional control

Biological control over coral skeletal composition is poorly understood but critically important to paleoenvironmental reconstructions. We present microanalytical measurements of trace-element abundances as well as oxygen and carbon isotopic compositions of individual skeletal components in the zooxanthellate coral Colpophyllia sp. Our data show that centers of calcification (COC) have higher trace element concentrations and distinctly lighter isotopic compositions than the fibrous components of the skeleton. These observations necessitate that COC and the fibrous skeleton are precipitated by different mechanisms, which are controlled by specialized domains of the calicoblastic cell-layer. Biological processes control the composition of the skeleton even at the ultra-structure level. Copyright 2006 by the American Geophysical Union.

Geophysical Research Letters↗

USGS2020

Genetic diversity targets and indicators in the CBD post-2020 Global Biodiversity Framework must be improved

The 196 parties to the Convention on Biological Diversity (CBD) will soon agree to a post-2020 global framework for conserving the three elements of biodiversity (genetic, species, and ecosystem diversity) while ensuring sustainable development and benefit sharing. As the most significant global conservation policy mechanism, the new CBD framework has far-reaching consequences- it will guide conservation actions and reporting for each member country until 2050. In previous CBD strategies, as well as other major conservation policy mechanisms, targets and indicators for genetic diversity (variation at the DNA level within species, which facilitates species adaptation and ecosystem function) were undeveloped and focused on species of agricultural relevance. We assert that, to meet global conservation goals, genetic diversity within all species, not just domesticated species and their wild relatives, must be conserved and monitored using appropriate metrics . Building on suggestions in a recent Letter in Science (Laikre et al., 2020) we expand argumentation for three new, pragmatic genetic indicators and modifications to two current indicators for maintaining genetic diversity and adaptive capacity of all species, and provide guidance on their practical use. The indicators are: 1) the number of populations with effective population size above versus below 500, 2) the proportion of populations maintained within species, 3) the number of species and populations in which genetic diversity is monitored using DNA-based methods. We also present and discuss Goals and Action Targets for post-2020 biodiversity conservation which are connected to these indicators and underlying data. These pragmatic indicators and goals have utility beyond the CBD; they should benefit conservation and monitoring of genetic diversity via national and global policy for decades to come.

Biological Conservation↗

USGS2021

A comprehensive statewide spatiotemporal stream assessment of per- and polyfluoroalkyl substances (PFAS) in an agricultural region of the United States

Public concern regarding per- and polyfluoroalkyl substances (PFAS) has grown substantially in recent years. In addition, research has documented multiple potential agriculture-related release pathways for PFAS (e.g., biosolids and livestock manure). Nevertheless, little research on the environmental prevalence of PFAS has been conducted in agricultural regions of the United States. To fill this gap, we conducted the first statewide spatiotemporal assessment of PFAS in Iowa streams across a region of intense agricultural activity. At least one PFAS was detected at 19 of the 60 stream sites sampled (32%) with 10 different PFAS detected statewide. The number of PFAS detected in the stream samples ranged from one to nine. While PFAS were detected in agricultural streams, sites with the most PFAS detected and in the highest concentration were small, effluent-affected streams where wastewater treatment plant discharge is driving stream PFAS concentrations. No individual PFAS had an exposure:activity ratio (EAR) of >1.0 (exposure concentration shown to trigger observed adverse biological activity). Five stream locations, however, had at least one EAR of >0.001, a precautionary effect screening threshold. Additional targeted temporal sampling would be beneficial to specifically capture potential agricultural source applications and corresponding runoff conditions to fully characterize the prevalence of PFAS in such agricultural systems.

Iowa↗

USGS2007

Carbon isotopic compositions of organic matter across continental Cretaceous-Tertiary (K-T) boundary sections: Implications for paleoenvironment after the K-T impact event

To assess the environmental perturbation induced by the impact event that marks the Cretaceous-Tertiary (K-T) boundary, concentrations and isotopic compositions of bulk organic carbon were determined in sedimentary rocks that span the terrestrial K-T boundary at Dogie Creek, Montana, and Brownie Butte, Wyoming in the Western Interior of the United States. The boundary clays at both sites are not bounded by coals. Although coals consist mainly of organic matter derived from plant tissue, siliceous sedimentary rocks, such as shale and clay, may contain organic matter derived from microbiota as well as plants. Coals record ??13C values of plant-derived organic matter, reflecting the ??13C value of atmospheric CO2, whereas siliceous sedimentary rocks record the ??13C values of organic matter derived from plants and microbiota. The microbiota ??13C value reflects not only the ??13C value of atmospheric CO2, but also biological productivity. Therefore, the siliceous rocks from these sites yields information that differs from that obtained previously from coal beds. Across the freshwater K-T boundary at Brownie Butte, the ??13C values decrease by 2.6??? (from - 26.15??? below the boundary clay to - 28.78??? above the boundary clay), similar to the trend in carbonate at marine K-T sites. This means that the organic ??13C values reflect the variation of ??13C of atmospheric CO2, which is in equilibrium with carbon isotopes at the ocean surface. Although a decrease in ??13C values is observed across the K-T boundary at Dogie Creek (from - 25.32??? below the boundary clay to - 26.11??? above the boundary clay), the degree of ??13C-decrease at Dogie Creek is smaller than that at Brownie Butte and that for marine carbonate. About 2??? decrease in ??13C of atmospheric CO2 was expected from the ??13C variation of marine carbonate at the K-T boundary. This ??13C-decrease of atmospheric CO2 should affect the ??13C values of organic matter derived from plant tissue. As such a decrease in ??13C value was not observed at Dogie Creek, a process that compensates the ??13C-decrease of atmospheric CO2 should be involved. For example, the enhanced contribution of 13C-enriched organic matter derived from algae in a high-productivity environment could be responsible. The ??13C values of algal organic matter become higher than, and thus distinguishable from, those of plant organic matter in situations with high productivity, where dissolved HCO3- becomes an important carbon source, as well as dissolved CO2. As the ??13C-decrease of atmospheric CO2 reflected a reduction of marine productivity, the compensation of the ??13C decrease by the enhanced activity of the terrestrial microbiota means that the microbiota at freshwater environment recovered more rapidly than those in the marine environment. A distinct positive ??13C excursion of 2??? in the K-T boundary clays is superimposed on the overall decreasing trend at Dogie Creek; this coincides with an increase in the content of organic carbon. We conclude that the K-T boundary clays include 13C-enriched organic matter derived from highly productive algae. Such a high biological productivity was induced by phenomena resulting from the K-T impact, such as nitrogen fertilization and/or eutrophication induced by enhanced sulfide formation. The high productivity recorded in the K-T boundary clays means that the freshwater environments (in contrast to marine environments) recovered rapidly enough to almost immediately (within 10??yr) respond to the impact-related environmental perturbations. ?? 2006 Elsevier B.V. All rights reserved.

Earth and Planetary Science Letters↗

USGS2011

Didymosphenia geminata: Algal blooms in oligotrophic streams and rivers

In recent decades, the diatom Didymosphenia geminata has emerged as nuisance species in river systems around the world. This periphytic alga forms large "blooms" in temperate streams, presenting a counterintuitive result: the blooms occur primarily in oligotrophic streams and rivers, where phosphorus (P) availability typically limits primary production. The goal of this study is to examine how high algal biomass is formed under low P conditions. We reveal a biogeochemical process by which D. geminata mats concentrate P from flowing waters. First, the mucopolysaccaride stalks of D. geminata adsorb both iron (Fe) and P. Second, enzymatic and bacterial processes interact with Fe to increase the biological availability of P. We propose that a positive feedback between total stalk biomass and high growth rate is created, which results in abundant P for cell division. The affinity of stalks for Fe in association with iron-phosphorus biogeochemistry suggest a resolution to the paradox of algal blooms in oliogotrophic streams and rivers. Copyright 2011 by the American Geophysical Union.

Geophysical Research Letters↗

USGS1988

The radiocarbon budget for Mono Lake: An unsolved mystery

Since 1957 the 14 C/C ratio of the dissolved inorganic carbon in Mono Lake has risen by about 60‰. The magnitude of this increase is about four times larger than that expected from the invasion of bomb-produced 14 C from the atmosphere. We have eliminated the following explanations: (1) measurement error, (2) an unusually high physical exchange rate for non-reactive gases, (3) inorganic enhancement of the CO 2 exchange rate, and (4) biological enhancement of the CO 2 exchange rate. Clandestine disposal of waste radiocarbon remains a dark-horse explanation. In the course of our investigations we have uncovered evidence for at least one episodic input of radiocarbon-free carbon to the lake over the last 1000 years. We speculate that this injection was related to a hydrothermal event resulting from sublacustrine volcanic activity.

Earth and Planetary Science Letters↗

USGS2002

The lizard fauna of Guam's fringing islets: Island biogeography, phylogenetic history, and conservation implications

We sampled the lizard fauna of twenty-two small islets fringing the Pacific island of Guam and used these data to shed light on the processes responsible for present-day diversity. Habitat diversity, measured by islet area and vegetation complexity, was significantly correlated with the number of species found on an islet. However, islet distance and elevation were not significant predictors of diversity. Distribution patterns were slightly different for the two major families in our sample, Scincidae and Gekkonidae: skinks needed larger islets to maintain a population than did geckos. Presence/absence patterns were highly and significantly nested, and population density was correlated with the number of islets on which a species was found. An area cladogram was poorly supported and showed no faunal similarity between nearby islands. These patterns indicate that extinctions on most islets were due mostly to non-catastrophic, long-acting biological causes. The presence on the islets of species extirpated on Guam and the lack of significant nestedness on islands with greater maximum elevation highlight the impact that predators (primarily brown treesnakes) can have. Our findings also show that small reserves will not suffice to protect endangered lizard faunas, and that the islets may serve as a short-term repository of such species until snake-free areas can be established on Guam.

Global Ecology and Biogeography Letters↗