Santa Cruz Island Research Articles

Translocation with targeted vaccination is the most effective strategy to protect an island endemic bird threatened by West Nile virus

AbstractAimInvasive pathogens are a growing conservation challenge and often occur in tandem with rapid environmental transformation, such as climate change, drought and habitat loss. Climate change appears to have facilitated the spread of West Nile virus (WNV), a cause of widespread avian mortality. WNV is considered the primary threat to island scrub‐jays (Aphelocoma insularis), endemic to Santa Cruz Island, California. Two approaches have been proposed to safeguard island scrub‐jays: (a) vaccination and (b) conservation translocation to re‐establish a second population on neighbouring Santa Rosa Island, hypothesized to have a lower risk of WNV. These alternatives operate at regional scales but exemplify global concerns with strategic implications for conservation biogeography and climate adaptation.LocationCalifornia Channel Islands, USA.MethodsWe compared the efficacy of vaccination and translocation strategies at minimizing 25‐year quasi‐extinction risk for island scrub‐jays using a stochastic population model.ResultsUnder current WNV‐free conditions, the predicted quasi‐extinction risk for island scrub‐jays was low (~0%) but increased to ≥22% with simulated WNV outbreaks. Vaccinating ≥60 individuals reduced risk to <5%, but risk doubled if population size declined and further increased with more frequent droughts. Translocation performed best if Santa Rosa Island had a large starting population size and habitat extent, and, more importantly, a low risk of WNV establishment; if Santa Rosa Island was inhospitable to WNV, quasi‐extinction risk dropped to near zero.Main conclusionsTranslocation with targeted vaccination during high‐risk conditions was the most effective strategy to protect island scrub‐jays from West Nile virus. Although vaccination often outperformed translocation, only scenarios that included a Santa Rosa population and vaccinations achieved acceptably low species‐wide extinction risk across all potential future conditions. Our analysis informs strategies to improve the long‐term viability of the most range‐restricted bird species in the continental United States and provides a model for assessing conservation‐translocation proposals for other species and threats.

Tribal allocation and biogeographical significance of one of the largest sigmodontine rodent, the extinct Galápagos Megaoryzomys (Cricetidae)

ABSTRACT One of the largest members of Sigmodontinae, the extinct Megaoryzomys curioi from Santa Cruz Island in the Galápagos Archipelago (Ecuador), is traditionally treated as a representative of Thomasomyini. We contrasted this hypothesis based on a direct study of craniodental material of M. curioi, including a well-preserved skull assessed through CT-scan examination, within a broader sampling of brachydonts sigmodontines. M. curioi lacks or presents a poorly expressed suspensory process of the squamosal bone, while in Thomasomyini this structure is well developed. In the same way, M. curioi does not exhibit the condition in the dorsal aperture of the ectotympanic displayed by the Thomasomyini, and the morphology of the mandible also contrasts with the widespread condition shown by Thomasomyini. Besides, the procingulum of the first lower molar in M. curioi lacks the typical pattern of Thomasomyini composed of two defined conulids. Overall craniodental morphology in M. curioi favours its allocation to the Oryzomyini. This alternative hypothesis resolves two biogeographical issues connected with the target genus: (1) Galápagos Islands were colonised by members of a single sigmodontine tribe (i.e., Oryzomyini) and (2) within the sigmodontine radiation; members of the Oryzomyini were uniquely capable of reaching oceanic islands.

Dog overpopulation on Santa Cruz Island, Galapagos 2018

AbstractIn addition to El Niño events, which can alter the pelagic food chain that supports growth and survival of sea lions, dog overpopulation, and diseases can cause further population declines in sea lions on the Galapagos. Knowledge of baseline data and evaluation of existing strategies to control dog reproduction are required for effective management of dog overpopulation on the archipelago. The main objective of the study reported here was to estimate the human: dog ratio on Santa Cruz Island, Galapagos in September 2018. In addition, dog demographic data were used to model the expected annual dog population growth in the next 3 years. The observed human: dog ratio was 756:187 (or 4.04:1) which extrapolates to 3,886 dogs; an increase of 55% in the dog population on Santa Cruz Island from 2014 to 2018. Study results show that current spay‐neuter efforts (about 180 dogs per year in the last 5 years; 57% females, 43% males) are not enough to keep the dog population stable (i.e., current baseline of 3,886 dogs in 2018). Our results justify a revision of current management action plan to control dog reproduction on Santa Cruz Island, Galapagos.

Saving Species: The Co-Evolution of Tortoise Taxonomy and Conservation in the Galápagos Islands

Abstract This article tells the stories behind the names of two species of Galápagos giant tortoise, Chelonoidis porteri and Chelonoidis donfaustoi, both of which inhabit Santa Cruz Island and which, until 2015, were considered one species, C. porteri. Taking a multispecies approach, it demonstrates how changing species designations reflect coevolving histories of science and conservation. Walter Rothschild assigned the name Testudo porteri in 1903 at a time when naturalists increasingly were concerned about the scarcity of animals they came to see as both endemic and endangered. Rothschild’s epithet honored US naval captain David Porter, the first person to write about differences among the Galápagos tortoises in the 1810s, which he noticed because his crews gathered tons of the animals as food stores for Pacific voyages. For Rothschild, saving species meant preserving them in his museum for the benefit of science before they were eaten. A century later, some of the C. porteri animals were renamed C. donfaustoi based on genetic studies of evolution and very different approaches to saving endangered species. This case study shows how nature, science, and conservation have coproduced species differently at different historical moments. By examining the changing practices through which species are enacted, this article outlines a framework by which environmental historians might productively engage with histories of science and science and technology studies to query just what species are, how they change, and with what consequences.

Linking rock age and soil cover across four islands on the Galápagos archipelago

The Galápagos Islands have been a place of preeminent scientific discoveries. The archipelago has formed on a tectonic plate moving over a volcanic hotspot, which has generated a chain of volcanic islands of different ages. This tectonic setting has favored the evolution of a unique flora and fauna on the islands; however, little is known on how it has influenced the formation and evolution of soils and belowground ecosystems. In order to enable the investigation of soil and ecosystem evolution, the aim of this study was to establish a soil chronosequence covering the full age range from the younger islands in the west to the older islands in the east of the archipelago. Six sites in the humid zones of the islands as well as two drier comparison sites were selected for this study. We characterized the geochemistry and mineralogy of the soil parent materials and constrained their ages using 14C (<10 ka) and 40Ar/39Ar dating. The parent materials are scoriaceous with bulk densities ≤1.6 g/cm3. Their major element composition is basaltic, including both alkali basalts and tholeiites. The scorias show amorphous contents between 20 and 85%, and their mineralogical composition is dominated by plagioclase and pyroxene. The numerical ages of the soil parent materials at the humid sites were: 1.45 ± 0.06 ka and 4.29 ± 0.09 ka on Isabela Island, 26 ± 7 ka on Floreana Island, 165.5 ± 11.6 ka on Santa Cruz Island, 825.6 ± 11.2 ka and 1070 ± 10 ka on San Cristóbal Island. Hence, the ages are distributed logarithmically covering a time span of approximately one million years. Along this chronosequence, we observed a non-linear increase in solum thickness, rubification degree and clay content with rock age. Changes were rapid in the initial phase of pedogenesis and more gradual in the later stages. Compared to the humid sites of the chronosequence, the pedogenic development at the dry comparison sites was much less advanced. The established chronosequence shall provide a solid basis for future studies on soil and ecosystem evolution in the unique environment of the Galápagos Islands.

Symbionts as Filters of Plant Colonization of Islands: Tests of Expected Patterns and Environmental Consequences in the Galapagos.

The establishments of new organisms that arrive naturally or with anthropogenic assistance depend primarily on local conditions, including biotic interactions. We hypothesized that plants that rely on fungal symbionts are less likely to successfully colonize remote environments such as oceanic islands, and this can shape subsequent island ecology. We analyzed the mycorrhizal status of Santa Cruz Island, Galapagos flora compared with the mainland Ecuador flora of origin. We experimentally determined plant responsiveness and plant–soil feedback of the island flora and assessed mycorrhizal density and soil aggregate stability of island sites. We found that a greater proportion of the native island flora species belongs to families that typically do not associate with mycorrhizal fungi than expected based upon the mainland flora of origin and the naturalized flora of the island. Native plants benefited significantly less from soil fungi and had weaker negative soil feedbacks than introduced species. This is consistent with the observation that field sites dominated by native plant species had lower arbuscular mycorrhizal (AM) fungal density and lower soil aggregate stability than invaded field sites at the island. We found support for a mycorrhizal filter to the initial colonization of the Galapagos.

First record of Hirsutella saussurei in the Galápagos Islands and first evidence parasitizing the invasive paper wasp, Polistes versicolor

Abstract In the present work we report the first occurrence of the entomogenous fungus Hirsutella saussurei, in the Galapagos Islands, and also the first evidence of this fungus parasitizing a new host: the invasive paper wasp Polistes versicolor. Some wasps parasitized by the fungus were found in Santa Cruz island in 2018 and 2019, while two new specimens were found in Floreana in 2019. Our data enlarge both the geographical distribution of the fungus and the host range. Even though P. versicolor is considered an important threat for the Galapagos endemic fauna, it is necessary a deep research to know if H. saussurei could be included under control programs of this invasive wasp.

Canine vector-borne disease in domestic dogs on Isla Santa Cruz, Galápagos.

Vector-borne diseases result in significant morbidity and mortality in domestic dogs in tropical and subtropical regions and also pose a potential threat to wildlife species and humans. Ehrlichia canis, the causative agent of canine monocytic ehrlichiosis (CME), has a high reported seroprevalence in dogs on Santa Cruz in the Galápagos Islands, Ecuador. Veterinary diagnostic and treatment resources are often scarce and clinical follow-up is lacking in the Galápagos. This study evaluated 58 dogs presenting to the Darwin Animal Doctors clinic in the city of Puerto Ayora on Santa Cruz Island during August of 2018. The seroprevalence of E. canis/Ehrlichia ewingii (48.3%), Anaplasma phagocytophilum/Anaplasma platys (12.1%), and Borrelia burgdorferi (0%), as well as the proportion of dogs actively infected with E. canis (12.1%) and E. ewingii (0%), are reported. Active infection was defined as the identification of antigen by PCR. Dogs with a packed cell volume (PCV)≤30% had a 10-fold risk of active infection with E. canis compared to dogs with a PCV≥31% (p=.0124). A PCV cutoff of 30% may be a useful screening tool for active E. canis infection in regions with high Ehrlichia seroprevalence, in the absence of other apparent causes of anemia. Dirofilaria immitis antigen was present in 6.9% of examined dogs, with the highest prevalence in the barrio Las Ninfas. PCR and Sanger sequencing were used to provide the first molecular identification of D. immitis in the Galápagos. This study updates the seropositivity and prevalence data of these canine vector-borne pathogens and highlights the need for continued surveillance in the region.

Two new Miocene limpets (Fissurellidae) from southern California, with notes on other fossil occurrences of the family in northwestern North America

Two new fissurellid limpets (Mollusca: Gastropoda: Fissurellidae), Fissurella? stantoni n. sp. and Scelidotoma aldersoni n. sp., are described from Miocene deposits in southern California. Fissurella? stantoni is described from a single specimen from the middle Miocene Topanga Canyon Formation in the Santa Monica Mountains, Los Angeles County, California. Scelidotoma aldersoni is described from two specimens, one from the middle Miocene Topanga Canyon Formation, and another provisionally (cf.) identified specimen of an internal mold from the middle Miocene “Vaqueros” Formation on Santa Cruz Island, Santa Barbara County, southern California. Other unreported fossil occurrences of Scelidotoma are a juvenile specimen attributed only to genus collected in the middle Eocene Crescent Formation in Washington state and S. bella from the Pliocene part of the San Diego Formation, San Diego County, California. The Scelidotoma occurrences extend the chronostratigraphic range of S. bella from the Holocene (living) to the middle Pliocene, and the range of the genus back to the middle Eocene.

Host phylogeny, diet, and habitat differentiate the gut microbiomes of Darwin\u2019s finches\xa0on Santa Cruz Island

Darwin’s finches are an iconic example of an adaptive radiation with well-characterized evolutionary history, dietary preferences, and biogeography, offering an unparalleled opportunity to disentangle effects of evolutionary history on host microbiome from other factors like diet and habitat. Here, we characterize the gut microbiome in Darwin’s finches, comparing nine species that occupy diverse ecological niches on Santa Cruz island. The finch phylogeny showed moderate congruence with the microbiome, which was comprised mostly of the bacterial phyla Firmicutes, Actinobacteria, and Proteobacteria. Diet, as measured with stable isotope values and foraging observations, also correlated with microbiome differentiation. Additionally, each gut microbial community could easily be classified by the habitat of origin independent of host species. Altogether, these findings are consistent with a model of microbiome assembly in which environmental filtering via diet and habitat are primary determinants of the bacterial taxa present with lesser influence from the evolutionary history between finch species.

Molecular characterization of Eimeria sp. from Galápagos giant tortoises (Chelonoidis spp.)

Galápagos giant tortoises are an essential component of their ecosystem and evaluation of parasites in their populations is essential for the management of conservation processes. Coccidiosis is the most common intestinal infection in free-living and captive reptiles. The aim of this study was to characterize molecularly the presence of Eimeria sp. in captive reared giant tortoises from Santa Cruz, Santiago, Española, and Pinzon Islands hatched and housed at the tortoise rearing center on Santa Cruz Island, Galápagos, by sequencing of the 18S rRNA gene. Galápagos. All samples were previously analyzed by coproparasitoscopic flotation technique and PCR for molecular identification. The results obtained by microscopy examination showed oocysts in all samples. PCR and sequencing indicated the presence Eimeria sp., showing a similarity percentage of 98% with Eimeria environmental. In conclusion, we identified a group of coccidia of the genus Eimeria sp. (MK909931) in Galápagos tortoises.

Population dynamics of an invasive bird parasite, Philornis downsi (Diptera: Muscidae), in the Galapagos Islands.

The invasive parasitic fly, Philornis downsi (Muscidae), is one of the greatest threats to the avifauna of the Galapagos Islands. The larvae of this fly feed on the blood and tissues of developing nestlings of at least 18 endemic and native birds. The aim of the current study was to investigate biotic and abiotic factors that may influence the population dynamics of this invasive parasite. To study the influence of vegetation zone and related climatic factors on fly numbers, a bi-weekly monitoring program using papaya-baited traps was carried out at a dry, lowland site and at a humid, highland site on Santa Cruz Island between 2012–2014. Female flies, a large proportion of which were inseminated and gravid, were collected throughout the year at both sites, indicating females were active during and between the bird breeding seasons. This is the first evidence that female flies are able to persist even when hosts are scarce. On the other hand, catch rates of male flies declined between bird breeding seasons. Overall, catch rates of P. downsi were higher in the drier, lowland habitat, which may be a consequence of host or resource availability. Time was a stronger predictor of adult fly numbers than climate, further suggesting that P. downsi does not appear to be limited by its environment, but rather by host availability. Seasonal catch rates suggested that populations in both habitats were continuous and multivoltine. Numbers of adult female flies appeared to be regulated chiefly by simple direct density dependence, and may be governed by availability of bird nests with nestlings. Nevertheless, confounding factors such as the existence of reservoir hosts that perpetuate fly populations and changes in behavior of P. downsi may increase the vulnerability of bird hosts that are already IUCN red-listed or in decline.

New Species of Flightless Cymatodera Gray, 1832 (Coleoptera: Cleridae: Tillinae) from the California Channel Islands

Two species of flightless Cymatodera Gray are described from the California Channel Islands: Cymatodera insularis Rifkind, new species, from Santa Catalina Island and San Clemente Island; and Cymatodera caterinoi Rifkind and Burke, new species, from Santa Rosa Island, Santa Cruz Island, and Anacapa Island. The new species are compared with Cymatodera vandykei Schaeffer and Cymatodera angustata Spinola, similar flightless species from the California mainland. The origins of Channel Island insect endemism are briefly discussed.

A matter of taste: Spatial and ontogenetic variations on the trophic ecology of the tiger shark at the Galapagos Marine Reserve.

Sharks are top predators across ocean food webs and have a major ecological role in marine ecosystems. Investigating the trophic ecology of this group of species is thus essential to understand ecosystem functioning and inform specific management actions aimed at shark conservation. The Galapagos Islands represent one of the last ocean wildernesses, where populations of sharks and other top marine predators come close to a pristine status. Here we provide the first study on the trophic ecology of the tiger shark (Galeocerdo cuvier) within the Galapagos Marine Reserve (GMR), using a combination of stable isotope analysis, satellite tracking, and passive acoustic telemetry to investigate ontogenetic and spatial variations at two regions. The mean estimated δ13C and δ15N at Isabela island (western region) were -13.9 ± 0.5‰ and 13.7 ± 0.7‰; and for Santa Cruz island (central region) were -13.8 ± 0.3‰ and 13.4 ± 0.7‰, respectively. Green sea turtles (Chelonia mydas) were the main prey item for large tiger sharks (>280 cm TL), while smaller sharks mainly fed on squid and pelagic fish. Tiger sharks exhibited a high degree of philopatry around green sea-turtle nesting areas, with the majority of sharks detected around green sea-turtle nesting areas for at least 10 months after their capture date, and some individuals were even present during the entire three-year study period. Although we did not report statistically significant differences between the two regions, isotopic and electronic tagging data suggest that tiger sharks in the Galapagos could be segregated into specific populations separated by geographical scales of <100 km. The high productivity of the archipelago, along with the protection from industrial fishing granted by the GMR, result in abundant and predictable sources of prey. This high food abundance, combined with the presence of suitable habitats throughout the tiger shark life cycle, might result in a reduction of migratory behaviours when compared to movement patterns of tiger sharks in other ocean basins. Additional studies using genetic tools could provide further evidence on the presence of separate management units, as it has been recently revealed for other shark species inhabiting the GMR.

Antimicrobial resistance genes present in the faecal microbiota of free-living Galapagos tortoises (Chelonoidis porteri).

Antimicrobial resistance (AMR), encoded by plasmid-mediated AMR genes (ARGs), is an increasing global public health threat. Wildlife play a fundamental role as sentinels, reservoirs and potential vectors of ARGs. For the first time in Galapagos, we have identified and quantified the presence of ARGs in free-living giant tortoises (Chelonoidis porteri). We performed ARG analyses by quantitative PCR of faeces collected from the cloaca of 30 tortoises widely distributed across Santa Cruz Island. Validated samples (n=28) were analysed by a panel of up to 21 different ARGs and all 28 tortoise samples were positive to one or more genes encoding resistance. Thirteen of 21 tested ARGs were present in at least one sample, and 10 tortoises (35.7%) had a multi-resistant pattern. We recommend additional research so we may more fully understand resistance patterns across taxa and geographical locations throughout the Galapagos archipelago, and the implications of ARGs for the health of wildlife, domestic animals, and humans. In this study, we found 100% of sampled giant tortoises had ARGs present in their faeces, suggesting a large-scale distribution of these genes within the archipelago.

Parched pines: a quantitative comparison of two multi‐year droughts and associated mass mortalities of bishop pine (Pinus muricata) on Santa Cruz Island, California

AbstractExtreme weather events such as droughts are expected to increase in severity and frequency as the climate changes; it is imperative that land managers be able to monitor associated changes in vegetation health efficiently and across large scales in order to mitigate or prepare for these events. This need motivated deeper study of the die‐off of bishop pine (Pinus muricata) on California's Santa Cruz Island during the 2012–2016 drought. These pines play a keystone role within the island's ecosystem and have experienced two severe droughts and associated mass die‐offs in the past 40 years. In an effort to compare these events, we used meteorological data to track changes in drought severity from 1985 to 2018 coupled with novel methods for forest monitoring to reveal dynamics not detectable by shorter‐duration studies. Leveraging 34 years of 30 m resolution Landsat imagery, we compared vegetation mortality between the two most severe droughts of that time period: 1987–1991 and 2012–2016. We used the slope of decline in the annual median value of three different Vegetation Indices (VIs; NBR, NDMI and NDVI) to compare mortality between the two drought events and to reveal spatial patterns of mortality within the bishop pine forests. Our results indicated that the 2012–2016 drought was the island's harshest in over a century and that it resulted in greater and more widespread mortality of vegetation within bishop pine stands than the 1987–1991 drought. The average VI decline was significantly greater during the 2012–2016 drought than the 1987–1991 drought by a factor of 1.89, 2.09 and 1.84 for NBR, NDMI and NDVI, respectively. Our results aligned with projections of increasing drought severity and associated tree mortality across the region. The temporal monitoring methods developed here can be adapted to study similar landscape scale changes over multiple decades in other forest ecosystems facing similar threats.

Antecedents to the Specialized Microdrill Industry on Santa Cruz Island, California

ABSTRACTThis report examines the development of lithic technology among the Chumash of California’s northern Channel Islands. By the middle of the first millennium A.D., the Island Chumash began to pursue specialized bead and drill making activities, leading to large-scale production of standardized artifact forms over much of the second millennium A.D. The region’s best provenanced collection of early ad hoc drills used for perforating Olivella shell beads is analyzed. These are flake drills, found in small numbers at late Middle Period (A.D. 650–1150) sites. Two sub-types (A and B) are identified that suggest technological development leading to formalized microdrills. It is suggested that bead makers at CA-SCRI-474 on the southern coast of Santa Cruz Island experimented with variations in drill forms throughout the early part of the late Middle Period. During the Transitional Period (A.D. 1150–1300), their techniques for Type B drills spread to CA-SCRI-191, a major bead-making center.

A Network‐Based Flow Accumulation Algorithm for Point Clouds: Facet‐Flow Networks (FFNs)

Flow accumulation algorithms estimate the steady state of flow on real or modeled topographic surfaces and are crucial for hydrological and geomorphological assessments, including delineation of river networks, drainage basins, and sediment transport processes. Existing flow accumulation algorithms are typically designed to compute flows on regular grids and are not directly applicable to arbitrarily sampled topographic data such as lidar point clouds. In this study we present a random sampling scheme that generates homogeneous point densities, in combination with a novel flow path tracing approach—the Facet‐Flow Network (FFN)—that estimates flow accumulation in terms of specific catchment area (SCA) on triangulated surfaces. The random sampling minimizes biases due to spatial sampling and the FFN allows for direct flow estimation from point clouds. We validate our approach on a Gaussian hill surface and study the convergence of its SCA compared to the analytical solution. Here, our algorithm outperforms the multiple flow direction algorithm, which is optimized for divergent surfaces. We also compute the SCA of a 6‐km2‐steep, vegetated catchment on Santa Cruz Island, California, based on airborne lidar point‐cloud data. Point‐cloud‐based SCA values estimated by our method compare well with those estimated by the D∞ or multiple flow direction algorithm on gridded data. The advantage of computing SCA from point clouds becomes relevant especially for divergent topography and for small drainage areas: These are depicted with much more detail due to the higher sampling density of point clouds.

Clustering River Profiles to Classify Geomorphic Domains

The structure and organization of river networks has been used for decades to investigate the influence of climate and tectonics on landscapes. The majority of these studies either analyze rivers in profile view by extracting channel steepness or calculate planform metrics such as drainage density. However, these techniques rely on the assumption of homogeneity: that intrinsic and external factors are spatially or temporally invariant over the measured profile. This assumption is violated for the majority of Earth's landscapes, where variations in uplift rate, rock strength, climate, and geomorphic process are almost ubiquitous. We propose a method for classifying river profiles to identify landscape regions with similar characteristics by adapting hierarchical clustering algorithms developed for time series data. We first test our clustering on two landscape evolution scenarios and find that we can successfully cluster regions with different erodibility and detect the transient response to sudden base level fall. We then test our method in two real landscapes: first in Bitterroot National Forest, Idaho, where we demonstrate that our method can detect transient incision waves and the topographic signature of fluvial and debris flow process regimes; and second, on Santa Cruz Island, California, where our technique identifies spatial patterns in lithology not detectable through normalized channel steepness analysis. By calculating channel steepness separately for each cluster, our method allows the extraction of more reliable steepness metrics than if calculated for the landscape as a whole. These examples demonstrate the method's ability to disentangle fluvial morphology in complex lithological and tectonic settings.

Determining the optimal grid resolution for topographic analysis on an airborne lidar dataset

Abstract. Digital elevation models (DEMs) are a gridded representation of the surface of the Earth and typically contain uncertainties due to data collection and processing. Slope and aspect estimates on a DEM contain errors and uncertainties inherited from the representation of a continuous surface as a grid (referred to as truncation error; TE) and from any DEM uncertainty. We analyze in detail the impacts of TE and propagated elevation uncertainty (PEU) on slope and aspect. Using synthetic data as a control, we define functions to quantify both TE and PEU for arbitrary grids. We then develop a quality metric which captures the combined impact of both TE and PEU on the calculation of topographic metrics. Our quality metric allows us to examine the spatial patterns of error and uncertainty in topographic metrics and to compare calculations on DEMs of different sizes and accuracies. Using lidar data with point density of ∼10 pts m−2 covering Santa Cruz Island in southern California, we are able to generate DEMs and uncertainty estimates at several grid resolutions. Slope (aspect) errors on the 1 m dataset are on average 0.3∘ (0.9∘) from TE and 5.5∘ (14.5∘) from PEU. We calculate an optimal DEM resolution for our SCI lidar dataset of 4 m that minimizes the error bounds on topographic metric calculations due to the combined influence of TE and PEU for both slope and aspect calculations over the entire SCI. Average slope (aspect) errors from the 4 m DEM are 0.25∘ (0.75∘) from TE and 5∘ (12.5∘) from PEU. While the smallest grid resolution possible from the high-density SCI lidar is not necessarily optimal for calculating topographic metrics, high point-density data are essential for measuring DEM uncertainty across a range of resolutions.