Species In Southern California Research Articles

Understanding Paleoclimate Through Southern California’s Packrat Middens

Documenting how ecosystems responded to climate change in the past can inform models for the future relevant to conservation decision-making. Packrat middens, or giant nests consisting of gathered plant material made by rodents of the genus Neotoma, represent one of the best data sources for understanding how plant communities change over time. These nests can be preserved for thousands of years, spanning episodes of glacial-interglacial variation, such as the Pleistocene-Holocene transition, or more recent fluctuations, such as the Little Ice Age and Medieval Warm Period. We used the USGS-NOAA paleoclimate open-access database to develop spatiotemporal reconstructions of plant species in Southern California, incorporating more than 242 individual middens with a total of 193 available radiocarbon dates spanning around 44,493 years cal BP. As a result, 374 plant species were identified within the SoCal middens, with Joshua Tree (Yucca brevifolia), Joint Pine (Ephedra species), and California Juniper (Juniperus californica) being the most abundant. We then applied these data to reconstruct past vegetation communities and contextualize a recently discovered asphaltic midden recovered from the La Brea Tar Pits (Los Angeles, California). The La Brea midden represents both the oldest and most coastal midden in our dataset in California and contains vegetation spanning Marine Isotope Stages 2-3. Ultimately, this research allows us to paint a picture of changing vegetation over time as a baseline for palaeoecological food web studies and can be compared with present day packrat nests found in this urban biodiversity hotspot. These data will be curated through the Conservation Paleobiology Network’s urban vegetation working group (based in Los Angeles, California) and made available for use by conservation and management projects throughout the region. With this information, CPN can implement habitat restoration projects in SoCal.

The Transition and Spread of a Chaparral Crown Fire: Insights from Laboratory Scale Wind Tunnel Experiments

Fire occurring in the chaparral behaves as a crown fire, a dual-layer fire that typically ignites in a dead surface fuel layer and transitions to an elevated live crown layer where it continues to spread. In chaparral fuels including chamise, a dominant species in southern California, flame transition to live crown fuels is associated with higher spread rates and greater fire intensity. Despite the relative importance of surface-to-crown transition and crown fire spread, most fire models represent chaparral fire as surface fire, therefore omitting key behavior processes driving this fire system. The purpose of this study was to characterize transition and spread behavior in chaparral fires modeled experimentally as crown fires. We examined heat release rate in the surface and crown fuel layers, time to transition, flame height, and rate of spread in wind-driven and nonwind-driven fires at two crown base heights. Our results showed that wind increased heat release rate, rate of spread, and flame height. A marked increase in heat release rate was observed in wind-driven fires, where adding wind produced an increase from 328 kW to 526 for a crown base height of 0.6 m and from 243 kW to 503 kW for a crown base height of 0.7 m. Further, crown base height served to decrease heat release rate and rate of spread for wind-driven and nonwind-driven fires.

Big Cats in the Big City: Spatial Ecology of Mountain Lions in Greater Los Angeles

ABSTRACTLarge carnivores can represent the ultimate challenge for conservation in developed landscapes because of their large area requirements and potential for conflict with humans. Some large carnivores such as mountain lions (Puma concolor) can use a wide range of biomes and vegetation types, and in southern California, USA, they persist in metropolitan Los Angeles, a megacity of 18 million people. Understanding how large carnivores use highly altered landscapes is important for their conservation and management. We estimated home range size, landscape use, and landscape selection for mountain lions in the Santa Monica Mountains and surrounding areas for 29 subadult and adult animals from 2002 to 2016, using 128,133 locations from global positioning system (GPS)‐collars. Home range size was similar to that reported by other researchers; home ranges averaged 372 km2 for adult males and 134 km2 for adult females, except for 2 adult males in isolated habitat fragments that maintained 2 of the smallest adult male home ranges ever recorded (24 km2 and 54 km2). Mountain lions very rarely entered developed areas, consistently avoided altered open areas such as golf courses, cemeteries, or other landscaped spaces, and showed a positive relationship between home range size and amount of development, all indicating that developed areas have reduced value for mountain lions. Mountain lions from all sex and age classes selected areas closer to development than expected by chance, which could be related to the presence of mule deer (Odocoileus hemionus) or other prey in or adjacent to urbanization. For 2 adult males that occupied home ranges within the most urban portions of our study area, their response to urban development differed strongly across diurnal periods, ranging from avoidance during the day to selection at night. Shrub vegetation types, especially chaparral, were important in terms of habitat use and resource selection, highlighting their importance for conservation of the species in southern California. North America's largest felid can thrive in shrublands and persist even in one of the world's largest cities, although they only very rarely venture into developed areas within that city. © 2021 The Wildlife Society.

New techniques for creating parthenogenetic larvae of the sea urchin Lytechinus pictus for gene expression studies.

Sea urchins are model organisms for studying the spatial-temporal control of gene activity during development. The Southern California species, Lytechinus pictus, has a sequenced genome and can be raised in the laboratory from egg to egg in 4 to 5 months. Here, we present new techniques for generating parthenogenetic larvae of this species and include a gallery of photomicrographs of morphologically abnormal larvae that could be used for transcriptomic analysis. Comparison of gene expression in parthenogenotes to larvae produced by fertilization could provide novel insights into gene expression controls contributed by sperm in this important model organism. Knowledge gained from transcriptomics of sea urchin parthenogenotes could contribute to parthenogenetic studies of mammalian embryos.

Spawning dynamics and egg production characteristics of captive Seriola dorsalis assessed using parentage analyses

In pelagic fish species, studying reproductive behaviour and spawning dynamics is challenging. In culture scenarios, these parameters are difficult to investigate for broadcast spawners such as Seriola. Hubbs-SeaWorld Research Institute has been culturing California yellowtail (S. dorsalis) since 2003 and now it is poised to become one of the first commercial offshore aquaculture marine finfish species in Southern California. Brood fish are typically kept in large tanks and spawn volitionally throughout the spawning season. This method is successful in yielding a consistent supply of eggs; however, it limits the understanding of spawning group dynamics or individual brood fish contribution, information that will be important to scaling production to commercial levels. In this study, genetic-based offspring parentage analyses were used to evaluate captive spawning dynamics in S. dorsalis over two consecutive spawning seasons. The analyses determined that typically one female released eggs during a spawning event, compared with an average of six males who released milt during these same spawning events. Notably, the analyses revealed that a single female dominated spawning output in both years, participating in 63 spawning events and producing 49.7 million eggs. The largest single spawn contribution by a female was 2.5 million eggs, corresponding to a batch fecundity estimate of 110,000 eggs kg−1. The spawning interval for the most productive females was 5–6 days. Using genetic tools to characterize spawning events will help to improve breeding programme designs for S. dorsalis, and this information can serve as a proxy for estimating spawning capacities of this species in the wild.

Sea urchin microbiomes vary with habitat and resource availability

AbstractSea urchins are key grazers in coastal seas, where they can survive a variety of conditions and diets, enhancing their ecological impact on kelp forests and other ecosystems. Using 16S rRNA gene sequencing, we characterized bacterial communities associated with guts of the two dominant sea urchin species in southern California, the red urchin Mesocentrotus franciscanus, and the purple urchin Strongylocentrotus purpuratus. Our results show that the two urchin species have distinct gut microbiomes that vary with habitat. The taxonomic composition of their microbiomes suggests that they may facilitate digestion of food and be a source of nutrition themselves. These results highlight the role of microbiomes within macroorganisms as an extended ecological trait, and suggest that microbes may be crucial to resource use and partitioning in co‐occurring species.

Oligomer and highly oxygenated organic molecule formation from oxidation of oxygenated monoterpenes emitted by California sage plants

Abstract. Plants emit a diverse range of biogenic volatile organic compounds (BVOCs) whose oxidation leads to secondary organic aerosol (SOA) formation. The majority of studies of biogenic SOA have focused on single or simple multicomponent BVOC mixtures thought to be representative of Northern hemispheric deciduous or mixed forest conditions. Gaps remain in our understanding of SOA formation from complex mixtures of real plant emissions in other environments. Towards the goal of understanding SOA in other regions, we conducted the first comprehensive study of SOA from oxygenated monoterpenes. These are the dominant emissions from the most common plant species in southern California's coastal sage ecosystem: black sage (Salvia mellifera) and California sagebrush (Artemisia californica). Emissions from sage plants, as well as single compounds representing their major emissions (camphor, camphene and eucalyptol), were oxidised in an Aerodyne potential aerosol mass oxidation flow reactor (PAM-OFR). The chemical composition of SOA was characterised using a high-resolution time-of-flight iodide-anion chemical-ionisation mass spectrometer equipped with a Filter Inlet for Gases and AEROsols (FIGAERO-I-HR-ToF-CIMS) under low- and medium-NOx conditions. SOA from oxygenated monoterpenes showed a higher-order oligomer content and a greater presence of highly oxygenated organic molecules (HOMs) than non-oxygenated monoterpenes, with HOM contributing 27 %–47 % and 12 %–14 % of SOA product signal from oxygenated and non-oxygenated monoterpenes respectively. This study highlights the potential importance of oxygenated monoterpene emissions for SOA formation in woody shrub ecosystems.

Slender salamanders (genus Batrachoseps) reveal Southern California to be a center for the diversification, persistence, and introduction of salamander lineages.

BackgroundThe southern California biodiversity hotspot has had a complex geological history, with both plate tectonic forces and sea level changes repeatedly reconfiguring the region, and likely driving both lineage splittings and extinctions. Here we investigate patterns of genetic divergence in two species of slender salamanders (Plethodontidae: Batrachoseps) in this region. The complex geological history in combination with several organismal traits led us to predict that these species harbor multiple ancient mitochondrial lineages endemic to southern California. These species belong to a clade characterized by fine-scale mitochondrial structure, which has been shown to track ancient splits. Both focal species, Batrachoseps major and B. nigriventris, are relatively widely distributed in southern California, and estimated to have persisted there across millions of years. Recently several extralimital populations of Batrachoseps were found in the San Joaquin Valley of California, a former desert area that has been extensively modified for agriculture. The origins of these populations are unknown, but based on morphology, they are hypothesized to result from human-mediated introductions of B. major.MethodsWe sequenced the mitochondrial gene cytochrome b from a geographically comprehensive sampling of the mitochondrial lineages of B. major and B. nigriventris that are endemic to southern California. We used phylogenetic analyses to characterize phylogeographic structure and identify mitochondrial contact zones. We also included the San Joaquin Valley samples to test whether they resulted from introductions. We used a bootstrap resampling approach to compare the strength of isolation-by-distance in both Batrachoseps species and four other salamander species with which they co-occur in southern California.ResultsThe northern lineage of B. major harbors at least eight deeply differentiated, geographically cohesive mitochondrial subclades. We identify geographic contact between many of these mtDNA lineages and some biogeographic features that are concordant with lineage boundaries. Batrachoseps nigriventris also has multiple deeply differentiated clades within the region. Comparative analyses highlight the smaller spatial scales over which mitochondrial divergence accumulates in Batrachoseps relative to most other salamander species in southern California. The extralimital populations of Batrachoseps from the San Joaquin Valley are assigned to B. major and are shown to result from at least two independent introductions from different source populations. We also suggest that B. major on Catalina Island, where it is considered native, may be the result of an introduction. Some of the same traits that facilitate the build-up of deep phylogeographic structure in Batrachoseps likely also contribute to its propensity for introductions, and we anticipate that additional introduced populations will be discovered.

Differences in root phenology and water depletion by an invasive grass explains persistence in a Mediterranean ecosystem.

Flexible phenological responses of invasive plants under climate change may increase their ability to establish and persist. A key aspect of plant phenology is the timing of root production, how it coincides with canopy development and subsequent water-use. The timing of these events within species and across communities could influence the invasion process. We examined above- and belowground phenology of two species in southern California, the native shrub, Adenostoma fasciculatum, and the invasive perennial grass, Ehrharta calycina to investigate relative differences in phenology and water use. We used normalized difference vegetation index (NDVI) to track whole-canopy activity across the landscape and sap flux sensors on individual chaparral shrubs to assess differences in aboveground phenology of both species. To determine differences in belowground activity, we used soil moisture sensors, minirhizotron imagery, and stable isotopes. The invasive grass depleted soil moisture earlier in the spring and produced longer roots at multiple depths earlier in the growing season than the native shrub. However, Adenostoma fasciculatum produced longer roots in the top 10 cm of soil profile in May. Aboveground activity of the two species peaked at the same time. The fact that Ehrharta calycina possessed longer roots earlier in the season suggests that invasive plants may gain a competitive edge over native plants through early activity, while also depleting soil moisture earlier in the season. Depletion of soil moisture earlier by E. calycina suggests that invasive grasses could accelerate the onset of the summer drought in chaparral systems, assuring their persistence following invasion.

Space use and inferred spawning activity of three exploited gamefish species on a large artificial reef

AbstractIntense fishing pressure has led to changes in species composition, demography and the over‐exploitation of many coastal fishes. To restore populations, artificial reefs (ARs) are used with the assumption that new habitat will increase fish productivity. Kelp bass (Paralabrax clathratus), barred sand bass (P. nebulifer) and California sheephead (Semicossyphus pulcher) are three important recreational gamefish species in southern California. Home ranging behaviour, space use and spawning‐related activity of these three species were quantified on a large AR. Kelp bass used the largest amount of area, but space use was similar among species. While no spawning behaviour could be determined for sheephead, kelp bass exhibited two different activity patterns during spawning months and barred sand bass migrated (indicative of spawning). Results of this study indicate that this large AR is providing suitable habitat for these species, and spawning‐related activity could be a sign that this AR is meeting essential life history demands.

Genetic patterns in fragmented habitats: a case study for two Peromyscus species in southern California

Genetic patterns in fragmented habitats: a case study for two Peromyscus species in southern California

Rediscovery of the southern California endemic American Keeled Slug Anadenulus cockerelli (Hemphill, 1890) after a 68-year hiatus

ABSTRACTWe report the first records of the southern California endemic American Keeled Slug Anadenulus cockerelli (Hemphill, 1890) in 68 years. Due to the restricted range of this species and lack of recent detection, it has received a NatureServe conservation status of Critically Imperilled or Imperilled. This species has always been difficult to detect, and will likely continue to be. This may be the result of genuine rarity, or may be the result of being cryptic and occurring in a microhabitat only ephemerally accessible to humans. We created a Species Distribution Model for A. cockerelli, which strongly predicts its occurrence where it is known, as well as some locations where it is currently unknown, such as in the northern Peninsular Ranges and in the San Bernardino Mountains in California. Threats to the continued existence of this species in southern California include human encroachment and resulting habitat loss, the climate changing to be hotter and drier, increased fire frequency, oak death due to beetle infestation, and other introduced species. Anadenulus cockerelli should continue to be surveyed and monitored into the future in order to better understand its distribution and level of conservation concern.

Soil aggregate stability under chaparral species in southern California

Aggregation is a key soil property that increases infiltration and aeration, and reduces erosion and runoff. This study sought to determine the amount and sources of aggregation in soils under four common chaparral species in southern California: bigberry manzanita (Arctostaphylos glauca Lindl.), scrub oak (Quercus dumosa Nutt.), hoaryleaf ceanothus (Ceanothus crassifolius Torr.), and chamise (Adenostoma fasiculatum H. & A.). Research was conducted at the San Dimas Experimental Forest in the San Gabriel Mountains. Total water stable aggregation, determined by wet sieving, averaged 45% in A and 40% in B horizons and differences were not significant by soil horizon or under the four vegetation species. Organic matter, roots, fungal hyphae, macrofauna, and clay all contribute to soil aggregation, but none of these is a clear, dominant, overriding factor in these soils. Development of water stable aggregation is inhibited by low densities of earthworms, relatively frequent wildfires, and soil erosion on the steep slopes in this chaparral ecosystem.

Quercivorol as a lure for the polyphagous and Kuroshio shot hole borers, Euwallacea spp. nr. fornicatus (Coleoptera: Scolytinae), vectors of Fusarium dieback.

The polyphagous shot hole borer and Kuroshio shot hole borer, two members of the Euwallacea fornicatus species complex (Coleoptera: Curculionidae: Scolytinae), are invasive ambrosia beetles that harbor distinct species of Fusarium fungal symbionts. Together with the damage caused by gallery construction, these two phytopathogenic Fusarium species are responsible for the emerging tree disease Fusarium dieback, which affects over 50 common tree species in Southern California. Host trees suffer branch dieback as the xylem is blocked by invading beetles and fungi, forcing the costly removal of dead and dying trees in urban areas. The beetles are also threatening natural riparian habitats, and avocado is susceptible to Fusarium dieback as well, resulting in damage to the avocado industries in California and Israel. Currently there are no adequate control mechanisms for shot hole borers. This paper summarizes efforts to find a suitable lure to monitor shot hole borer invasions and dispersal. Field trials were conducted in two counties in Southern California over a span of two years. We find that the chemical quercivorol is highly attractive to these beetles, and perform subsequent field experiments attempting to optimize this lure. We also explore other methods of increasing trap catch and effects of other potential attractants, as well as the deterrents verbenone and piperitone.

Evaluations of Insecticides and Fungicides for Reducing Attack Rates of a new invasive ambrosia beetle (Euwallacea Sp., Coleoptera: Curculionidae: Scolytinae) in Infested Landscape Trees in California.

A recently discovered ambrosia beetle with the proposed common name of polyphagous shot hole borer (Euwallacea sp., Coleoptera: Curculionidae: Scolytinae), is reported to attack >200 host tree species in southern California, including many important native and urban landscape trees. This invasive beetle, along with its associated fungi, causes branch dieback and tree mortality in a large variety of tree species including sycamore (Platanus racemosa Nutt.). Due to the severity of the impact of this Euwallacea sp., short-term management tools must include chemical control options for the arboriculture industry and private landowners to protect trees. We examined the effectiveness of insecticides, fungicides, and insecticide-fungicide combinations for controlling continued Euwallacea sp. attacks on previously infested sycamore trees which were monitored for 6 mo after treatment. Pesticide combinations were generally more effective than single pesticide treatments. The combination of a systemic insecticide (emamectin benzoate), a contact insecticide (bifenthrin), and a fungicide (metconazole) provided some level of control when applied on moderate and heavily infested trees. The biological fungicide Bacillus subtilis provided short-term control. There was no difference in the performance of the three triazole fungicides (propiconazole, tebuconazole, and metconazole) included in this study. Although no pesticide combination provided substantial control over time, pesticide treatments may be more effective when trees are treated during early stages of attack by this ambrosia beetle.

Range Expansion of the Eastern Fox Squirrel within the Greater Los Angeles Metropolitan Area (2005 – 2014) and Projections for Continued Range Expansion

Abstrac Monitoring the spread and distribution of introduced species in an area can be challenging due to a variety of issues. Range expansion may exceed expected rates if the area of introduction is more suitable than expected, and may be slowed by an area in which it is difficult to establish a population. The species of interest in this study is the Eastern Fox Squirrel (Sciurus niger rufiventer) and the focus of the study is the spread of the species in Southern California. Previous studies have shown a steady and continuous spread from main points of introduction in Southern California and the species is now considered well established in the region. In this study, we collected and mapped new location data within Southern California. We discuss the spread of the Eastern Fox Squirrel in this area from 2005 through 2014 and include habitat suitability models to project the potential future distribution of the species. Results show that the Eastern Fox Squirrel has spread east into Rancho Cucamonga, int...

Preliminary Report: Effects of black mustard allelopathy on the fitness and life history strategies of buffalo gourd in southern California

Abstract. The allelopathic compounds secreted into the soil by Brassica nigra (L.) W. D. J. Koch (black mustard) serve to reduce seed germination rates and plant fitness in nearby species. As such, B. nigra shares in an amensalistic relationship with most of the species within range of its allelopathic interference. However, Cucurbita foetidissima (buffalo gourd) is a native species in southern California that has managed to persist within and around areas invaded by B. nigra. We hypothesized that increased proximity to B. nigra would negatively impact C. foetidissima fitness and alter life history strategies. We found that C. foetidissima growing in close proximity to B. nigra had smaller fruit volume, a lower number of seeds per fruit, lower dry seed weight, a higher number of seeds per cubic centimeter, and a higher number of seeds per gram of fruit than C. cucurbita that grew outside of the allelopathic range of B. nigra. The reproductive strategy of C. cucurbita also appeared to change from K-selecti...

Mosquito Capture Rate Using CO2-Baited Traps in Relation to Distance From Water and Height: Implications for Avian Disease Transmission.

Accumulating evidence suggests that enzootic transmission of pathogens such as West Nile virus (WNV) by mosquitoes is governed by host-bird interactions, including mosquito preferences for specific species and developmental stages of host birds, host bird availability, and host defensive behavior. Here, we examined how the attack rate of five mosquito species in southern California was influenced by the position of CO2-baited traps in relation to distance from water and trap height. We identified 44,207 female mosquitoes representing five species: Aedes vexans Meigen, Anopheles franciscanus McCracken, Anopheles hermsi Barr & Guptavanij, and the two most abundant species which are also WNV vectors, Culex erythrothorax Dyar and Culex tarsalis Coquillett. Mosquito captures decreased markedly with trap height, and also decreased with distance from a riparian area but not with distance from an open water source lacking a vegetated border. The results of this study suggest that WNV-competent ornithophilic mosquitoes may amplify the virus especially in reservoir birds that roost or nest close to the ground and near riparian vegetation.

Environmental suitability for Agrilus auroguttatus (Coleoptera: Buprestidae) in Mexico using MaxEnt and database records of four Quercus (Fagaceae) species

Abstract The goldspotted oak borer Agrilus auroguttatus Schaeffer is an invasive pest of three Quercus species in southern California, U.S.A. As a native and potentially indigenous exotic species, its distribution and potential damage is largely unknown in Mexico. We used the maximum entropy algorithm to determine the bioclimatic variables that may explain the distribution of A. auroguttatus, as well as its interaction with the distribution of known hosts in Mexico. Our model calculated high suitability for A. auroguttatus in the biogeographical provinces of California, the northern and southern areas of Sierra Madre Occidental and the northwestern area of the Mexican Plateau; moderate suitability was projected in the Baja California, Sonora and Sierra Madre Occidental provinces. Potential distribution of A. auroguttatus was overlapping with native ranges of Quercus agrifolia, Quercus emoryi Torrey and Quercus hypoleucoides A. Camus. Precipitation of the coldest quarter (23.6%), isothermality (23.5%), precipitation seasonality (17.3%) and mean temperature of the coldest quarter (11.2%) contributed most to explaining its distribution in Mexico. The geographical interaction (i.e. the likelihood that the habitat would be suitable for coexistence) of A. auroguttatus with its hosts in Mexico was projected in the California province (46 382.60 km2, probably as an exotic species) and the northwestern areas of Mexican Plateau and Sierra Madre Occidental provinces (74 013.45 km2, probably as native). Determining the areas of environmental suitability for A. auroguttatus and its host distribution can focus ground surveys, contribute to management efforts and assist in the development of risk assessments for Mexico.

Using wildfires as a natural experiment to evaluate the effect of fire on southern California vernal pool plant communities

Fires in Mediterranean-type ecosystems (MTEs) have been studied widely with emphasis on shrub and grassland vegetation types. Although vernal pools comprise a very small fraction of MTEs, they are important to regional biodiversity due to high local endemism. Fire frequency has been increasing in MTEs and while altered fire regimes have been shown to threaten native shrub communities, their effect on vernal pools is uncertain. Due to the number of at-risk species in this habitat, experiments with potentially harmful effects are problematic. Therefore, we initiated this study to take advantage of two anthropogenic but unplanned fire events. The analysis uses data collected from 2001 to 2009 on a site burned in 2000 and 2003. We analyzed the data in an exploratory framework and applied unadjusted and adjusted models using different parameterizations of the exposure variables. The results did not provide evidence that fire reduced the abundance of native vernal pool species in southern California. There is provisional evidence of a positive but temporary effect of fire on native vernal pool species. Our analysis demonstrates an exploratory analytical approach for use with problematic data sets that can arise when conservation objectives constrain opportunities for experimental studies.