Scott A. Morrison

Scatter-hoarding corvids as seed dispersers for oaks and pines: A review of a widely distributed mutualism and its utility to habitat restoration

ABSTRACT Seed dispersal mutualisms with scatter-hoarders play a crucial role in population dynamics of temperate large-seeded trees. These behaviors shape seed dispersal patterns, which can be applied to conservation of populations, communities, and even ecosystems dominated by large-seeded trees. We draw on a growing body of literature to describe the ecological context and consequences of scatter-hoarding as a seed dispersal mechanism. We synthesize the quantitative literature on the interaction between members of the avian family Corvidae (crows, ravens, jays, magpies, and nutcrackers) and nut-bearing trees such as pines (Pinus spp.) and oaks (Quercus spp.) to examine unique aspects of avian scatter-hoarders as seed dispersers. During the scatter-hoarding process, seed selectivity, transportation distance, hoarding frequency, and cache placement affect seed dispersal effectiveness, a measure of the quantity and quality of dispersal. Case studies from around the world highlight the role of corvid seed dispersal in population dynamics of trees, and how the birds scatter-hoarding behavior can be facilitated for the restoration of oak- and pine-dominated habitats. This mutualism, which provides many plant species with long-distance, high-quality seed dispersal, will likely become even more important for conservation of oak and pine ecosystems as suitable climates shift rapidly in the decades ahead. This ecosystem service provided by corvids could therefore serve as an efficient conservation tool.

Proactive Conservation Management of an Island-endemic Bird Species in the Face of Global Change

Biodiversity conservation in an era of global change and scarce funding benefits from approaches that simultaneously solve multiple problems. Here, we discuss conservation management of the island scrub-jay (Aphelocoma insularis), the only island-endemic passerine species in the continental United States, which is currently restricted to 250-square-kilometer Santa Cruz Island, California. Although the species is not listed as threatened by state or federal agencies, its viability is nonetheless threatened on multiple fronts. We discuss management actions that could reduce extinction risk, including vaccination, captive propagation, biosecurity measures, and establishing a second free-living population on a neighboring island. Establishing a second population on Santa Rosa Island may have the added benefit of accelerating the restoration and enhancing the resilience of that islands currently highly degraded ecosystem. The proactive management framework for island scrub-jays presented here illustrates how strategies for species protection, ecosystem restoration, and adaptation to and mitigation of climate change can converge into an integrated solution.

Argentine Ant Management in Conservation Areas: Results of a Pilot Study

Abstract. n Argentine ants (Linepithema humile) have invaded many areas of conservation concern, including half of the California Channel Islands. On Santa Cruz Island, the species has invaded approximately 2% of the island, and the infestations are expanding. Argentine ants displace many other invertebrates, and their expansion throughout the island could lead to the extirpation of native invertebrate species and the disruption of key ecological processes (e.g., plant-pollinator interactions and seed dispersal). We describe a treatment protocol to manage or eliminate Argentine ants on Santa Cruz Island developed by The Nature Conservancy and the National Park Service, in collaboration with academic and pest control specialists. We combined low-concentration toxicant baits with efficient dispersal methods to treat landscape-scale Argentine ant infestations in rugged terrain and dense vegetation with minimal impact to nontarget species. From May to October 2012, we applied our baiting protocol within 2 study sites, totaling 7.8 ha on Santa Cruz Island. In May 2013, one year post treatment, we observed >99% reduction in Argentine ant activity in treatment plots compared to untreated plots, using 2 different monitoring techniques. While further testing and monitoring is needed, these results suggest this protocol may be an effective tool to eliminate Argentine ant infestations from this type of habitat and terrain.

ANNUAL SURVIVORSHIP OF THE SEDENTARY RUFOUS-CROWNED SPARROW (AIMOPHILA RUFICEPS): NO DETECTABLE EFFECTS OF EDGE OR RAINFALL IN SOUTHERN CALIFORNIA

Abstract The Rufous-crowned Sparrow (Aimophila ruficeps) is a nonmigratory passerine that displays an area-sensitive distribution pattern of abundance in fragmented coastal sagescrub habitat of southern California. To determine if habitat fragmentation negatively affected adult survival, we used Cormack-Jolly-Seber models to compare annual survival probabilities of adult sparrows breeding in habitat adjacent to urban-developed edges to those of birds breeding in the interior of large habitat expanses in San Diego County, 1997–2000. During that period, an El Niño event brought heavy rainfall to the study area, and a La Niña event brought drought. Annual survival probabilities were relatively high for a small passerine (females: 0.69 ± 0.05 SE; males: 0.74 ± 0.04 SE) but, given our data, did not differ between habitat types or with rainfall. Annual resighting probabilities for the birds were strongly associated with variation in rainfall, being high in the wet year and low in the dry year. Mate- and site-fidelity were apparently high, and surveys during the nonbreeding season documented that the sparrows stayed paired and on territories year-round. We hypothesize that the high apparent survivorship of this species is related to its nonmigratory habit and its tendency to curtail reproductive effort during periods of food scarcity. Although our survivorship analysis suggests that the urban-wildland interface does not adversely affect survival of territorial Rufous-crowned Sparrows, our power to detect an effect of habitat edge on survival was low. Thus, we urge caution in concluding that edge effects do not have an ecologically important influence on survival rates in this species.

Reproductive Ecology of the Island Scrub-Jay

Abstract. n We investigated the reproductive ecology of the Island Scrub-Jay (Aphelocoma insularis), which is endemic to Santa Cruz Island, California, and is a species of conservation concern. We documented daily nest survival, probability of renesting, annual fledging success, and breeding behavior, and determined how these factors varied in relation to the habitat characteristics of the jays home ranges. Clutch sizes, feeding rates, and nest attendance were not correlated with chaparral cover or with home-range size. In contrast, nest predation, which accounted for 92% of documented nest failures, was less likely at nests that were more concealed, at nests of breeding pairs with home ranges that were smaller and had a greater proportion of taller vegetation, and at nests that were initiated earlier in the breeding season. Researchers activity near nests increased the likelihood of predation, although the effect diminished with a nests age. Despite relatively low nest survival, the high frequency of renesting allowed pairs to fledge an average of 1.1 ± 0.1 young per year, or 1.8 ± 0.2 young after the effects of the observer were accounted for. Currently, chaparral habitats on Santa Cruz Island are regenerating following the removal of exotic herbivores. This regeneration could in turn increase and improve breeding habitat for this island endemic.

Identifying Evolutionarily Significant Units and Prioritizing Populations for Management on Islands

Abstract. n Islands host exceptionally high levels of endemism compared to mainland regions and are subject to disproportionately high rates of extinction and imperilment. Therefore, the protection and preservation of taxonomic units that are endemic to islands is a key component in mitigating the loss of global biodiversity. However, determining what is “endemic” on islands can be challenging. Conservation units are commonly delineated based on genetic divergence at neutral loci (e.g., genetic differentiation at microsatellite loci or reciprocal monophyly based on mitochondrial genes). Island populations of nonvolant species are expected to meet this criterion, regardless of adaptive differences, due to geographic isolation, founder effects, and small effective population sizes. We therefore argue that the delineation and management of island endemic populations should not be based on neutral genetic divergence and reciprocal monophyly alone. Instead, we recommend identifying island populations that have genetically based adaptations to their unique environments. A comprehensive framework specifically designed to delineate evolutionarily significant units (ESUs) on islands should be based on metrics of both neutral and adaptive genetic divergence. The California Channel Islands host several taxa considered to be endemic, and we highlight 2 case studies to illustrate how this framework can be applied. This approach can be applied broadly to continental islands and island archipelagos, enabling conservation practitioners to use an objective framework to prioritize units of biological diversity for management.

On the Fast Track to Recovery: Island Foxes on the Northern Channel Islands

Abstract. n The island fox (Urocyon littoralis) represents an unusual case of a species that achieved virtual recovery a mere 15 years after population declines were first discovered. Island fox subspecies on San Miguel, Santa Rosa, and Santa Cruz islands declined precipitously in the mid-1990s due to predation by Golden Eagles (Aquila chrysaetos), which had not historically bred on the islands. In 2008, a 10-year period of recovery action implementation ended. The recovery program had included captive breeding and reintroduction of island foxes and capture and relocation of Golden Eagles. Free-ranging fox populations have been monitored to assess recovery of each subspecies and to detect potential threats of disease and predation. Monitoring included (1) annual grid trapping to allow estimation of annual population size via capture-mark-recapture methods and (2) systematic surveillance of radio-collared foxes to allow estimation of mortality rates and causes. A comprehensive demographic modeling effort produced a population recovery tool that uses adult mortality and population size estimates from the monitoring programs to estimate extinction risks for each fox population. The tool allows managers to assess when threats are sufficiently mitigated to consider populations acceptably safe from extinction. Population monitoring indicates that island foxes on the northern Channel Islands have increased up to 30-fold from population lows and that annual survival has been 90% or better in most years. The San Miguel and Santa Cruz subspecies have approached or reached predecline population levels, and application of the recovery tool indicates they will be biologically recovered by 2013. Biological recovery of the Santa Rosa subspecies, hindered by predation which caused lower survival in 2010, will occur by 2017.

Stand Structure and Acorn Production of the Island Scrub Oak (Quercus pacifica)

Abstract. n Island scrub oak (Quercus pacifica), a keystone chaparral species on Santa Rosa, Santa Cruz, and Santa Catalina islands, provides habitat for a diverse assemblage of plant and animal species. The restoration of oak habitat is a management priority, but little is known about Q. pacifica stand structure and acorn production, 2 parameters that are important in the species recovery. To investigate whether species interactions and abiotic conditions have an effect on stand structure and acorn production, we sampled within-stand densities, tree sizes, and acorns in the 3 island populations that have been exposed to different herbivores, seed predators, and climate conditions. Stand densities varied more within than between islands; but Santa Rosa, the coldest of the 3 islands, had smaller trees with smaller acorns than the other 2 islands. To quantify the temporal and spatial variation in acorn production on Santa Cruz Island, we conducted acorn counts at 2 spatial scales: (1) an island-wide survey of 200 trees along the east—west axis of the island (2008–2012) and (2) small-scale surveys within three 100-ha study plots (150 trees; 2009–2012). Acorn production varied strongly, both temporally and spatially, with little temporal synchrony and spatial autocorrelation. Trees at higher elevations produced more acorns, but the roles of temperature and precipitation were unclear in this relatively short study. To increase our understanding of the drivers of Q. pacifica acorn production, we propose that annual oak surveys be incorporated into a long-term monitoring program across the California Channel Islands.

Strategies for Biosecurity on a Nearshore Island in California

Abstract. n Islands provide refuge for many rare and endemic species but are especially vulnerable to invasion by nonnative species. Invasive alien species are a major factor in the imperilment and extinction of island biota. Biosecurity protocols are designed to prevent or quickly detect the transport of harmful nonnative species, with the goal of eliminating the high economic cost of invasive species removal and the biological cost of damage caused by nonnative organisms. Effective biosecurity protocols require a balanced approach to on-island monitoring, off-island surveillance and prevention practices, rapid response, and educational outreach. Here we use the biosecurity program on Santa Cruz Island, California, to illustrate how risk evaluation, program priorities, and funding constraints intersect to define programmatic scope. Santa Cruz Island land managers have chosen to invest in early detection programs such as remote camera trapping, off-island prevention and education, and rapid-response planning for rats and in on-island biosecurity to prevent the spread of the most harmful plant species. We suggest that biosecurity efforts will be more effective—as well as cost effective—as an archipelago-wide initiative than as a single-island program. A newly formed collaboration with managers of other California Islands is designed to enhance visibility of the biosecurity initiative and attract new funding sources. With the economy afforded by collaboration, we will expand our program and prioritize annual audits, augment educational programs, measure project success, and increase compliance with and effectiveness of biosecurity protocols.

Reintroduction of Historically Extirpated Taxa on the California Channel Islands

Abstract. n Most invasive alien vertebrate populations on the Channel Islands of California have been eradicated over the past 30 years. Unfortunately, removal of these introduced herbivores or predators came too late for some native flora and fauna, and numerous populations are now extinct. Here, we describe a systematic approach to reintroducing extirpated native taxa as a means for rebuilding natural communities and enhancing the resiliency of island ecosystems. Reintroduction efforts typically focus on a single species or site. In contrast, we propose that if reintroduction is a shared conservation goal of managers across the islands, the associated planning, implementation, and monitoring should be conducted as a cross-island initiative for the archipelago. A coordinated effort based on best practices in reintroduction biology could accrue programmatic efficiencies and economies of scale, more quickly advance ecosystem and species conservation goals, and create unique opportunities to test hypotheses in basic and applied ecology and evolution. The philosophical and technical approaches developed through this program may apply to other island and mainland systems and could be adapted to develop conservation strategies for species that may be candidates for assisted colonization in the face of climate change.