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Chaparral of California

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Urbanization has dramatically altered habitats for local species worldwide. While some species are unable to meet the challenges that these alterations bring, others are able to persist as long as a threshold for suitable habitat is met. For reptiles, a key feature for persistence in urban areas can be access to suitable refuges from predation, high temperatures, and/or other environmental challenges. We tested for effects of local and landscape variables affecting urban occupancy in the Western Fence Lizard, Sceloporus occidentalis, in transects across an urban–rural gradient, with a specific focus on the presence of rock, tree, and shrub refuges. We found that fence lizards were much more likely to be present in areas with more rock cover, and in parks or low-density residential areas. Occupancy was also positively related to canopy cover in the general vicinity, though negatively related to number of trees along the transects. Our results highlight the importance of assessing local habitat features to successfully predict the occupancy of reptile species in urban habitats, and present directions for future research with concrete conservation and management applications.
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Premise: Does the seed size-seed number allocation trade-off model apply to long-term persistent soil seed banks? This trade-off between seed size versus number of seeds produced is usually applied at a single population on an annual basis. Our question is how this model might apply to close relatives that produce dormant seed forming long-term persistent soil seed banks. These two criteria allow a focus on divergent evolution of conspecifics and permits us to isolate seed size in the spectrum of life history traits that may be influencing seed traits, and on how seed size influences accumulation and persistence in the soil. Methods: In California, Arctostaphylos species only produce physiologically dormant seed that are fire-stimulated and that vary in seed size permitting seed size-seed bank density relationship as a test of the seed size-seed number allocation model. Soil seed banks of 10 species of Arctostaphylos were sampled with fruit volumes ranging from 21-1063 mm3 . Seed bank density was determined by hand extraction from soil samples. Results: We found that seed bank densities were significantly negatively related to fruit or seed size. Conclusions: Rather than an issue of allocational trade-off between size and number, we interpret these results as reflecting seed predation and postfire seedling establishment. Seed bank densities, even after decades, generally were less than one or two-year's seed production, suggesting intense seed predation. Burial by scatter-hoarding rodents provided sufficient seeds deep enough for survival of fire. Variation on seed size suggests seedling establishment constraints, but it needs further research.
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California chaparral is one of four sclerophyllous shrublands in North America, each with their own unique climatic patterns, but sharing a common history and similar plant taxa. Traditionally, California chaparral has been viewed in context with other Mediterranean climate plant communities. This view has generally ignored the remarkable relationship California chaparral has with the continent's three other sclerophyllous shrublands: Sonoran chaparral in Arizona, Madrean-Oriental chaparral in west Texas, and mexical in Mexico, reaching as far south as Oaxaca. By comparing chaparral within the context of other North American sclerophyllous shrublands, rich, new areas of research can be facilitated. This is especially important because California chaparral is the most widely distributed habitat within the California Floristic Province, a designated biodiversity hotspot. We present a new model for chaparral ecology that moves away from the current focus on the chaparral's relationship to fire, encouraging a wider examination of many other attributes of chaparral ecology including biodiversity, interactions between plant and animal species, and the value of old-growth chaparral. This wider examination can also enhance new approaches to studying the chaparral's natural fire regime, now limited to comparing pre- and post-European contact periods. Developing a more ecologically-based definition of California chaparral that appreciates all successional processes in the system, as well as its intrinsic value, is crucial to protecting what is left of the region's intact sclerophyllous shrublands.
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A new oribatid mite genus, Sculpteremaeus gen. nov. (Oribatida, Cymbaeremaeidae), with Sculpteremaeus olszanowskii sp. nov. as type species, is proposed and described based on adults. It is from sandy soil-litter in chaparral of California, USA, an environment from which no oribatid mites have been recorded previously. Based on an analysis of adults of all genera of Cymbaeremaeidae, the new genus is closely related to Ametroproctus, from which it is most easily distinguished by the morphology of lamellae, size of lamellar cusps, and shape of the tutorium. We expand the Cymbaeremaeidae family diagnosis, and question the inclusion of Scapheremaeus based on extensive molecular evidence showing its closer relationship with Ameronothroidea and Licneremaeoidea.
Chapter
California chaparral, a sclerophyllous shrub-dominated plant community shaped by a Mediterranean-type climate and infrequent, high-intensity fire, is one of the most biodiverse and threatened habitats on Earth. Distinct forms of chaparral, distinguished by differing species composition, geography, and edaphic characteristics, can cover thousands of hectares with dense vegetation or be restricted to smaller communities identified by the presence of endemic species. To maintain the biodiversity of chaparral, protective land management actions will be required to mitigate the loss due to the impacts of human population growth, development, climate change, and increased fire frequencies.
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State and federal agencies have reported fire causes since the early 1900s, explicitly for the purpose of helping land managers design fire-prevention programs. We document fire-ignition patterns in five homogenous climate divisions in California over the past 98 years on state Cal Fire protected lands and 107 years on federal United States Forest Service lands. Throughout the state, fire frequency increased steadily until a peak c. 1980, followed by a marked drop to 2016. There was not a tight link between frequency of ignition sources and area burned by those sources and the relationships have changed over time. Natural lightning-ignited fires were consistently fewer from north to south and from high to low elevation. Throughout most of the state, human-caused fires dominated the record and were positively correlated with population density for the first two-thirds of the record, but this relationship reversed in recent decades. We propose a mechanistic multi-variate model of factors driving fire frequency, where the importance of different factors has changed over time. Although ignition sources have declined markedly in recent decades, one notable exception is powerline ignitions. One important avenue for future fire-hazard reduction will be consideration of solutions to reduce this source of dangerous fires.
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Del Mar manzanita (Arctostaphylos glandulosa Eastw. subsp. crassifolia (Jeps.) P.V. Wells) is a federally listed endangered shrub found in San Diego County, California and Baja California, Mexico. This manzanita forms part of the imperiled southern maritime chaparral of southwestern California and adjacent Baja California, Mexico. Del Mar manzanita is problematic to identify because of morphological intergradation with other subspecies of A. glandulosa. Such intergradation could result from biological phenomena, such as gene flow among subspecies. Alternatively, it could be that the current circumscription of the Del Mar manzanita is not correct, and that the morphological characters used to diagnose this subspecies are inaccurate indicators of underlying genetics. This situation leads to problems for conservation planning, where accurate identification of individual plants is essential. Here, we used high-throughput sequencing of restriction-site associated DNA markers (RADseq) to develop single nucleotide polymorphism (SNP) data for a large sample of putative Del Mar manzanita, and a small sample of closely related subspecies of A. glandulosa. We analyzed genetic relationships using a total of 65,964 SNPs, with the aim of testing whether morphological traits used to identify Del Mar manzanita are an accurate reflection of underlying genetic patterns. We conclude that vegetative morphology is a poor predictor of genetic patterns, and that the current morphology-based circumscription of Del Mar manzanita is probably in need of some change. However, due to the limited sampling of A. glandulosa subspecies in this study, it is not possible to determine the taxonomic limits of Del Mar manzanita using our SNP data.
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Anthropogenic disturbances can constrain the realized niche space of wildlife by inducing avoidance behaviors and altering community dynamics. Human activity might contribute to reduced partitioning of niche space by carnivores that consume similar resources, both by promoting tolerant species while also altering behavior of species (e.g. activity patterns). We investigated the influence of anthropogenic disturbance on habitat and dietary niche breadth and overlap among competing carnivores, and explored if altered resource partitioning could be explained by human-induced activity shifts. To describe the diets of coyotes, bobcat, and gray foxes, we designed a citizen science program to collect carnivore scat samples in low- (‘wildland’) and high- (‘interface’) human-use open space preserves, and obtained diet estimates using a DNA metabarcoding approach. Habitat use was determined at scat locations. We found that coyotes expanded habitat and dietary niche breadth in interface preserves, whereas bobcats and foxes narrowed both niche breadth measures. High human use was related to increased dietary niche overlap among all mesocarnivore pairs, increased coyote habitat overlap with bobcats and foxes, and a small reduction in habitat overlap between bobcats and foxes. The strongest increase in diet overlap was among coyotes and foxes, which was smaller in magnitude than their habitat overlap increase. Finally, coyote scats were more likely to contain nocturnal prey in interface preserves, whereas foxes appeared to reduce consumption of nocturnal prey. Our results suggest that dominant and generalist mesocarnivores may encroach on the niche space of subordinate mesocarnivores in areas with high human activity, and that patterns in resource use may be related to human-induced activity shifts.
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Growing human and ecological costs due to increasing wildfire are an urgent concern in policy and management, particularly given projections of worsening fire conditions under climate change. Thus, understanding the relationship between climatic variation and fire activity is a critically important scientific question. Different factors limit fire behavior in different places and times, but most fire-climate analyses are conducted across broad spatial extents that mask geographical variation. This could result in overly broad or inappropriate management and policy decisions that neglect to account for regionally specific or other important factors driving fire activity. We developed statistical models relating seasonal temperature and precipitation variables to historical annual fire activity for 37 different regions across the continental United States and asked whether and how fire-climate relationships vary geographically, and why climate is more important in some regions than in others. Climatic variation played a significant role in explaining annual fire activity in some regions, but the relative importance of seasonal temperature or precipitation, in addition to the overall importance of climate, varied substantially depending on geographical context. Human presence was the primary reason that climate explained less fire activity in some regions than in others. That is, where human presence was more prominent, climate was less important. This means that humans may not only influence fire regimes but their presence can actually override, or swamp out, the effect of climate. Thus, geographical context as well as human influence should be considered alongside climate in national wildfire policy and management.
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The relationship between annual variation in area burned and seasonal temperatures and precipitation was investigated for the major climate divisions in California. Historical analyses showed marked differences in fires on montane and foothill landscapes. Based on roughly a century of data, there are five important lessons on fire-climate relationships in California: (1) seasonal variations in temperature appear to have had minimal influence on area burned in the lower elevation, mostly non-forested, landscapes; (2) temperature has been a significant factor in controlling fire activity in higher elevation montane forests, but this varied greatly with season - winter and autumn temperatures showed no significant effect, whereas spring and summer temperatures were important determinants of area burned; (3) current season precipitation has been a strong controller of fire activity in forests, with drier years resulting in greater area burned on most United States Forest Service (USFS) lands in the state, but the effect of current-year precipitation was decidedly less on lower elevation California Department of Forestry and Fire Protection lands; (4) in largely grass-dominated foothills and valleys the magnitude of prior-year rainfall was positively tied to area burned in the following year, and we hypothesise that this is tied to greater fuel volume in the year following high rainfall. In the southern part of the state this effect has become stronger in recent decades and this likely is due to accelerated type conversion from shrubland to grassland in the latter part of the 20th century; (5) the strongest fire-climate models were on USFS lands in the Sierra Nevada Mountains, and these explained 42-52% of the variation in area burned; however, the models changed over time, with winter and spring precipitation being the primary drivers in the first half of the 20th century, but replaced by spring and summer temperatures after 1960.
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Historical data are essential for understanding how fire activity responds to different drivers. It is important that the source of data is commensurate with the spatial and temporal scale of the question addressed, but fire history databases are derived from different sources with different restrictions. In California, a frequently used fire history dataset is the State of California Fire and Resource Assessment Program (FRAP) fire history database, which circumscribes fire perimeters at a relatively fine scale. It includes large fires on both state and federal lands but only covers fires that were mapped or had other spatially explicit data. A different database is the state and federal governments' annual reports of all fires. They are more complete than the FRAP database but are only spatially explicit to the level of county (California Department of Forestry and Fire Protection - Cal Fire) or forest (United States Forest Service - USFS). We found substantial differences between the FRAP database and the annual summaries, with the largest and most consistent discrepancy being in fire frequency. The FRAP database missed the majority of fires and is thus a poor indicator of fire frequency or indicators of ignition sources. The FRAP database is also deficient in area burned, especially before 1950. Even in contemporary records, the huge number of smaller fires not included in the FRAP database account for substantial cumulative differences in area burned. Wildfires in California account for nearly half of the western United States fire suppression budget. Therefore, the conclusions about data discrepancies and the implications for fire research are of broad importance.
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Mediterranean-type ecosystems (MTEs) are found today in southwestern Australia, the Cape Region of South Africa, the Mediterranean Basin, California, and central Chile. These MTEs possess the highest levels of plant species richness in the world outside of the wet tropics. These ecosystems include a variety of vegetation structures that range from the iconic mediterranean-type shrublands to deciduous and evergreen woodlands, evergreen forests, and herblands and grasslands. Sclerophyll vegetation similar to today’s mediterranean-type shrublands was already present on oligotrophic soils in the wet and humid climate of the Cretaceous, with fire-adapted Paleogene lineages in southwestern Australia and the Cape Region. The novel mediterranean-type climate (MTC) seasonality present since the middle Miocene has allowed colonization of MTEs from a regional species pool with associated diversification. Fire persistence has been a primary driving factor for speciation in four of the five regions. Understanding the regional patterns of plant species diversity among the MTEs involves complex interactions of geologic and climatic histories for each region as well as ecological factors that have promoted diversification in the Neogene and Quaternary. A critical element of species richness for many MTE lineages has been their ability to speciate and persist at fine spatial scales, with low rates of extinction. Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics Volume 47 is November 01, 2016. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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We describe two new subspecies of the widespread shrub Arctostaphylos. One subspecies is a southern extension of A. purissima; A. purissima subsp. globosa V.T. Parker and M.C. Vasey. It differs from the nominate species in several ways, but principally in having glandular hairs on the young stems and inflorescences and having a globose fruit typically with fused nutlets. We also describe a new subspecies of A. patula; A. patula subsp. gankinii M.C. Vasey and V.T. Parker. Arctostaphylos patula subsp. gankinii is a distinctive variant of the montane greenleaf manzanita that occurs widely at various localities in the Sierra Nevada extending into the inner North Coast, Klamath, and Siskiyou ranges of California and southern Oregon. This new subspecies appears to have been identified incorrectly as A. manzanita subsp. roofii and subspecies of A. mewukka in herbarium collections. The patterns of diversity for both species and their subspecies illustrate common taxonomic issues in the genus, representin...
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Climate and weather have long been noted as playing key roles in wildfire activity, and global warming is expected to exacerbate fire impacts on natural and urban ecosystems. Predicting future fire regimes requires an understanding of how temperature and precipitation interact to control fire activity. Inevitably this requires historical analyses that relate annual burning to climate variation. Fuel structure plays a critical role in determining which climatic parameters are most influential on fire activity, and here, by focusing on the diversity of ecosystems in California, we illustrate some principles that need to be recognized in predicting future fire regimes. Spatial scale of analysis is important in that large heterogeneous landscapes may not fully capture accurate relationships between climate and fires. Within climatically homogeneous subregions, montane forested landscapes show strong relationships between annual fluctuations in temperature and precipitation with area burned; however, this is strongly seasonal dependent; e.g., winter temperatures have very little or no effect but spring and summer temperatures are critical. Climate models that predict future seasonal temperature changes are needed to improve fire regime projections. Climate does not appear to be a major determinant of fire activity on all landscapes. Lower elevations and lower latitudes show little or no increase in fire activity with hotter and drier conditions. On these landscapes climate is not usually limiting to fires but these vegetation types are ignition-limited. Moreover, because they are closely juxtaposed with human habitations, fire regimes are more strongly controlled by other direct anthropogenic impacts. Predicting future fire regimes is not rocket science; it is far more complicated than that. Climate change is not relevant to some landscapes, but where climate is relevant, the relationship will change due to direct climate effects on vegetation trajectories, as well as by feedback processes of fire effects on vegetation distribution, plus policy changes in how we manage ecosystems.
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Seed-caching rodents have long been seen as important actors in dispersal ecology. Here, we focus on the interactions with plants in a fire-disturbance community, specifically Arctostaphylos species (Ericaceae) in California chaparral. Although mutualistic relationships between caching rodents and plants are well studied, little is known how this type of relationship functions in a disturbance-driven system, and more specifically to systems shaped by fire disturbance. By burying seeds in the soil, rodents inadvertently improve the probability of seed surviving high temperatures produced by fire. We test two aspects of vertical dispersal, depth of seed and multiple seeds in caches as two important dimensions of rodent-caching behavior. We used a laboratory experimental approach to test seed survival under different heating conditions and seed bank structures. Creating a synthetic soil seed bank and synthetic fire/heating in the laboratory allowed us to have control over surface heating, depth of seed in the soil, and seed cache size. We compared the viability of Arctostaphylos viscida seeds from different treatment groups determined by these factors and found that, as expected, seeds slightly deeper in the soil had substantial increased chances of survival during a heating event. A key result was that some seeds within a cache in shallow soil could survive fire even at a depth with a killing heat pulse compared to isolated seeds; temperature measurements indicated lower temperatures immediately below caches compared to the same depth in adjacent soil. These results suggest seed caching by rodents increases seed survival during fire events in two ways, that caches disrupt heat flow or that caches are buried below the heat pulse kill zone. The context of natural disturbance drives the significance of this mutualism and further expands theory regarding mutualisms into the domain of disturbance-driven systems.
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Ecological factors favoring either postfire resprouting or postfire obligate seeding in plants have received considerable attention recently. Three ecological models have been proposed to explain patterns of these two life history types. In this study, we test these three models using data from California chaparral. We take an innovative approach to testing these models by not testing community or landscape patterns, but instead, investigating vegetation structure characteristic of four pairs of resprouting and (non-resprouting) obligate seeding subspecies of Arctostaphylos (Ericaceae), a dominant and diverse shrub genus in California chaparral. Data were analyzed for percentage bare ground, elevation, annual precipitation, number of fires, and time between fires and were compared independently for each subspecies pair. Results were consistently supportive of the gap-dependent model suggesting that obligate seeders are favored when post-disturbance gaps are large. Results were inconclusive or contrary to expectations for both of the other two models.
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We measured dieback and mortality in a chaparral shrub community at a chaparral/desert ecotone following four years of below-average rainfall. Ecotones are important systems in which to examine plant and community responses to extreme and prolonged drought conditions and the potential impact of global change on plant distributions and community composition. Following a particularly severe drought year, dieback and mortality were documented for seven co-dominant shrub species. We examined whether mortality was related to species ecology, leaf traits, or water relations. Dieback and mortality were greatest in two non-sprouting species. These species also had high xylem cavitation resistance and low specific leaf area compared to several sprouting species. Among two sprouting congeners, mortality was greater in the more shallowly rooted species, even though this species was more cavitation resistant. Across all species, those that were more resistant to cavitation had greater mortality. Evidently, high resistance to xylem cavitation does not prevent adult plant mortality at chaparral/desert ecotones. A series of extreme drought years could preferentially reduce or eliminate non-sprouting species from mixed chaparral populations, causing a shift in community structure and contributing to desertification.
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A phylogeny of Arctostaphylos (Ericaceae) was estimated using nuclear ribosomal ITS sequence data for 98 species, of which 83 were unique taxa and 15 were multiple samples of geographically widespread or morphologically variable species (A. uva-ursi, A. patula, A. pungens, A. manzanita, A. glandulosa, and A. tomentosa). Forty-four ingroup taxa shared an identical sequence. The remaining species showed pairwise substitution rates of 2.4% or less, and 17 taxa had sequences with polymorphic positions. Maximum parsimony analysis recovered a large polytomy and three small clades. Analysis of a reduced data set with the 17 polymorphic taxa removed recovered a two-clade topology with some additional resolution within each clade. Four taxa showed patterns of sequence nucleotide additivity suggesting interspecific hybrid origin. A proposed hypothesis of higher rates of nucleotide substitution in species that are obligate seeders vs. those that are facultative sprouters could not be tested due to shared sequences. Low interspecific sequence variability in the nuclear ribosomal ITS region in Arctostaphylos may be due to several factors, including recent diversification of the genus in California, long generation time between sexual reproduction events, and rapid concerted evolution of nuclear ribosomal ITS arrays in both diploids and tetraploids.
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Exploring the role of fire in each of the five Mediterranean-type climate ecosystems, this book offers a unique view of the evolution of fire-adapted traits and the role of fire in shaping Earth's ecosystems. Analyzing these geographically separate but ecologically convergent ecosystems provides key tools for understanding fire regime diversity and its role in the assembly and evolutionary convergence of ecosystems. Topics covered include regional patterns, the ecological role of wildfires, the evolution of species within those systems, and the ways in which societies have adapted to living in fire-prone environments. Outlining complex processes clearly and methodically, the discussion challenges the belief that climate and soils alone can explain the global distribution and assembly of plant communities. An ideal research tool for graduates and researchers, this study provides valuable insights into fire management and the requirements for regionally tailored approaches to fire management across the globe. © J. E. Keeley, W. J. Bond, R. A. Bradstock, J. G. Pausas and P. W. Rundel 2012.
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Because of their influence on succession and other community interactions, large-scale, infrequent natural disturbances also should play a major role in mutualistic interactions. Using field data and experiments, I test whether mutualisms have been incorporated into large-scale wildfire by whether the outcomes of a mutualism depend on disturbance. In this study a seed dispersal mutualism is shown to depend on infrequent, large-scale disturbances. A dominant shrubland plant (Arctostaphylos species) produces seeds that make up a persistent soil seed bank and requires fire to germinate. In post-fire stands, I show that seedlings emerging from rodent caches dominate sites experiencing higher fire intensity. Field experiments show that rodents (Perimyscus californicus, P. boylii) do cache Arctosta-phylos fruit and bury most seed caches to a sufficient depth to survive a killing heat pulse that a fire might drive into the soil. While the rodent dispersal and caching behavior itself has not changed compared to other habitats, the environmental transformation caused by wild-fire converts the caching burial of seed from a dispersal process to a plant fire adaptive trait, and provides the context for stimulating subsequent life history evolution in the plant host.
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Human-driven declines of apex predators can trigger widespread impacts throughout ecological communities. Reduced apex predator occupancy or activity can release mesopredators from intraguild competition, with unknown repercussions on the ecological community. As exurban development continues to expand worldwide, it is important to document how mesopredators are impacted by the combined influences of apex predators and humans. We used motion-detecting camera traps to examine spatial and temporal patterns of meso-and apex predator occupancy and activity in a fragmented landscape in California. We hypothesized that both spatial and temporal partitioning among the carnivore guild would be affected by varied levels of human influence. We found that higher residential development reduced puma occupancy but was not related to the occupancy of mesopredators. Bobcats, grey foxes, and Virginia opossums were detected more often at sites occupied by pumas, whereas coyotes and raccoons were detected less often. The detection probabilities of smaller mesopredators were related to coyotes, a dominant mesopredator, but the magnitude and direction of these correlations differed depending upon puma occupancy. We also found that species altered their activities temporally in locations with higher human use, with pumas, bobcats and coyotes reducing diurnal activities and increasing nocturnal ones. These activity shifts were reflected in reduced temporal partitioning between intraguild competitors, with unknown effects on species interactions and repercussions to the prey community. Our results suggest that human development and activity alters predator community structure through both direct and indirect pathways. Therefore effective carnivore conservation requires an understanding of how mesopredators respond to varying levels of apex predator and anthropogenic influences.
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Germination behavior of 45 tree, shrub, subshrub, and liana taxa from fire-prone coastal sage scrub and chaparral was investigated. Nearly 1/3 of the species had seeds that germinated readily upon wetting, and germination was not further stimulated by any fire-related cue. Most coastal sage subshrubs germinate readily in the absence of fire-related stimuli and can thus colonize other forms of disturbance. For many of these species, germination was inhibited in the dark. This may result in a portion of the seed pool remaining dormant until fire since, in the case of several species, dark inhibition is overcome by charate. Chaparral shrubs and trees that germinate readily upon wetting seldom establish seedlings after fire. Seedling establishment and population expansion for such species is dependent upon extended fire-free periods. In contrast, woody species that fail to germinate without some fire-related cue have seedling establishment and potential population expansion restricted to postfire conditions. -from Author
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This study describes changes in the abundance of shrub species after two fires in 1979 and 1980 on Otay Mountain in San Diego County, California. The 1979 fire burned a large area of dense chaparral and coastal sage scrub. The 1980 fire burned a portion of the 1979 fire area that had been seeded with annual ryegrass (Lolium multiflorum) as an erosion protection measure. Changes in the vegetation caused by the 1979 fire alone were similar to those commonly seen in chaparral wildfire, but the reburning of the vegetation in 1980 caused drastic changes in some areas. Ceanothus oliganthus was almost completely eliminated from the area of the 1980 burn. Adenostoma fasciculatum, the most abundant shrub at the study site, was reduced in density by up to 97%. Even Xylococcus bicolor, which normally resprouts with complete success after fire, suffered substantial mortality with reburning. It is concluded that the changes brought about by the 1980 fire will certainly persist for many decades. While sudden shifts in vegetation composition probably occurred without human intervention, we believe that human activity, especially after the introduction of aggressive annual grasses 200 yr ago, has caused an increase in the instances of abrupt change.
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Animal community structure influences plant community structure in many ways, one of which is varying post-dispersal seed predation rates by different, sometimes distantly related animal taxa. In fire-prone mediterranean-climate vegetation, such as California chaparral, rodents are commonly assumed to be the most effective post-dispersal seed predators, which would render them the main driver for soil seed bank dynamics. This is a critical issue because the most dominant species of the chaparral rely on dormant, persistent soil seed banks to recruit after wildfires. Here, we used a series of exclusion experiments in combination with close video observation to show that granivorous birds are more effective than rodents in removing seeds of Ceanothus papillosus, a fire-dependent obligate seeder shrub of the California chaparral. We furthermore used seed traps and germination experiments to show that C. papillosus can have extremely high seed production and expresses strong intra and inter-annual seed bank dynamics. We conclude in contrast to other studies, that granivorous birds, in addition to rodents, are major determinants of C. papillosus seed bank densities. We also found that seed bank density increased between years, despite high seed predation rates. We conclude that high seed production in combination with small and dark seed design may help some seeds to stay undetected, thus allowing C. papillosus to build a sufficiently dense enough seed bank to regenerate after wildfire. Our results indicate that the ratio of granivorous birds to rodents has the potential to play a major role in shaping chaparral community structure by differentially impacting soil seed bank densities.
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This study compares postfire regeneration and diversity patterns in fire-prone chaparral shrublands from mediterranean (California) and non-mediterranean-type climates (Arizona). Vegetation sampling was conducted in tenth hectare plots with nested subplots for the first two years after fire. Floras in the two regions were compared with Jaccard's Index and importance of families and genera compared with dominance-diversity curves. Although there were 44 families in common between the two regions, the dominant families differed; Poaceae and Fabaceae in Arizona and Hydrophyllaceae and Rosaceae in California. Dominance diversity curves indicated in the first year a more equable distribution of families in Arizona than in California. Woody plants were much more dominant in the mediterranean climate and herbaceous plants more dominant in the bimodal rainfall climate. Species diversity was comparable in both regions at the lowest spatial scales but not at the tenth hectare scale. Due to the double growing season in the non-mediterranean region, the diversity for the first year comprised two different herbaceous floras in the fall and spring growing seasons. The Mediterranean climate in California, in contrast, had only a spring growing season and thus the total diversity for the first year was significantly greater in Arizona than in California for both annuals and herbaceous perennials. Chaparral in these two climate regimes share many dominant shrub species but the postfire communities are very different. Arizona chaparral has both a spring and fall growing season and these produce two very different postfire floras. When combined, the total annual diversity was substantially greater in Arizona chaparral.
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High diversity and endemism in the California Floristic Province (CFP) are an alleged response to the late Cenozoic advent of Mediterranean-type climate in this region. Ceanothus comprises two divergent subgenera with centers of diversity in the CFP. We reconstruct the evolution of Ceanothus by using DNA sequence data from the nuclear gene nitrate reductase. We find that the timing of diversification events is related to geological and climatic history. In both subgenera, diversification is characterized by recent divergence of extant taxa and geographically structured phylogenetic relationships. A strong north-south divergence of subgenus Cerastes across the Transverse Ranges indicates that phylogenetic relationships may be structured by climatically divergent regions of the CFP. Divergence-time estimation suggests that the age of extant diversification in both subgenera is ∼6 Ma. This agrees with the fossil record but predates the hypothesized Quaternary (2-Ma) origin of Mediterranean-type climate in the region.
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During the 1997-1998 El Nino, record rainfall triggered.150 shallow landslides within a 9.5 km2 area near Santa Barbara, Cal- ifornia. They were studied to analyze the sediment delivery to val- ley floors from landslides in coastal sage scrub and converted grasslands. The conversion of coastal sage to grasslands, primarily to provide pasturage for cattle, is common in the region, and the landscape's response may affect water quality, reservoir infilling, and debris flow hazards. We explore the relationship between lateral- root reinforcement and landslide volume by developing a slope- stability analysis that incorporates root cohesion along the sides of the failure. The stability analysis correctly predicts an inverse re- lationship between landslide volume and hillslope angle in the sage. The volumes of failures in the grasslands do not vary systemati- cally with slope and are generally smaller than those in the sage. From aerial-photograph analysis and field mapping, we find that there are 22.9 failures per square kilometer in the grasslands com- pared to 13.2 failures per square kilometer in the sage. Despite the lower failure density in the coastal sage, greater failure volumes and longer transport distances delivered more sediment to valley floors, with a specific volumetric flux of 2.8 3 10 -2 m 3 ·m -1 for this El Nino compared to 1.73 10 -2 m 3 ·m -1 in the grasslands. We con- clude that the conversion from vegetation with stronger and deeper roots (coastal sage) to vegetation with weaker and shallower roots (grass) has caused a pulse of increased landsliding in the grasslands because the soils are currently too thick for the prevailing root reinforcement. We suggest that, over time, soils in the grassland hollows will become thinner as the evacuation by landslides is re- peated until the landsliding rate declines to balance the soil sup- plied from local colluvium production and diffusive processes upslope.
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Aim Rainfall reliability has been neglected as a determinant of plant trait convergence and divergence in mediterranean-climate ecosystems. This paper reports on patterns of rainfall reliability — quantified as interannual variation in monthly and seasonal rainfall, and as the frequency of individual events in terms of their size, duration and intensity — for four fire-prone mediterranean-climate ecosystems. Location The four mediterranean-climate regions of the world with fire-prone ecosystems, namely SW Cape (South Africa), SW Australia, California and the Mediterranean Basin (Andalusia, Spain). Methods Using long-term monthly rainfall data from stations dispersed across the four regions, we computed monthly means and interannual variation for each month of the year — the latter quantified as the coefficient of variation (CV) — and divided these into winter and summer seasons. We also computed the mean number of rainfall events, the mean frequency in various categories of event duration (days), the amount of rainfall per event (mm) and the rainfall intensity per event (mm/day) per year for winter and summer seasons for a subset of the rainfall stations. Results The fraction of rain falling in summer was lowest in California (5%) and similarly low (c. 25%) in the other three regions. The hierarchy of values of coefficient of variation (CV) of monthly rainfall during the winter period was as follows: California > Andalusia >> SW Cape > SW Australia; results for summer were: California > > Andalusia >> SW Australia ∼ SW Cape. SW Australian sites experienced the greatest frequency of short, small and low-intensity rainfall events in both seasons; patterns in the SW Cape were intermediate between Australia and the two northern hemisphere sites which both received fewer, larger and more intense events. Overall, the two southern hemisphere regions (SW Australia and the SW Cape) had significantly more reliable regimes than the two northern hemisphere ones (Mediterranean Basin and California). Main conclusions These differences in rainfall reliability regimes may provide a novel perspective on the distribution of certain plant life-history traits in mediterranean-climate ecosystems. Less reliable regimes would select for germination and seedling survival traits that enable persistence of genets in the face of uncertain moisture conditions during the winter and spring establishment phase. Study systems that accommodate for phylogenetic constraints, namely invasive species derived from mediterranean-climate ecosystems, as well as shared lineages, provide good opportunities to develop and test hypotheses on the implication of different rainfall reliability regimes. One of the novel implications of this study is that the distinctive trait of assemblages in the southern hemisphere regions may be a consequence not so much of their shared nutrient-poor soils as of their similarly reliable rainfall regimes.
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Chapter
California chaparral, a sclerophyllous shrub-dominated plant community shaped by a Mediterranean-type climate and infrequent, high-intensity fire, is one of the most biodiverse and threatened habitats on Earth. Distinct forms of chaparral, distinguished by differing species composition, geography, and edaphic characteristics, can cover thousands of hectares with dense vegetation or be restricted to smaller communities identified by the presence of endemic species. To maintain the biodiversity of chaparral, protective land management actions will be required to mitigate the loss due to the impacts of human population growth, development, climate change, and increased fire frequencies.
Chapter
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With rapid development and the spread of urbanized land, there is an increasing need to understand species' responses to urban conditions. Carnivores are considered to be sensitive to urbanization; however, there is ample evidence that some carnivore species successfully inhabit urban areas, and human-modified habitats have recently been recognized as an important refuge for several species.Despite the increasing number of studies on urban carnivore ecology, no comprehensive cross-species comparisons have been made in order to assess the effects of urbanization on the spatial ecology of carnivores and their population densities. Such a review could provide interesting insight into how some carnivore species respond to increasing urbanization. Specifically, we examine changes in population density and home range size of eight carnivore species that occur along the natural–urban environmental gradient.Using data from 411 articles, we provide evidence that the home range size of carnivores decreases in six out of eight species, and population density increases in three out of six species along the natural–urban habitat gradient. The density-dependent pattern of variation in home range size is consistent in all species studied.Our results emphasize the remarkable ability of some carnivore species to adapt to novel environments through their behavioural flexibility and life history adaptations. We outline ideas for future research that could be adopted in addressing this phenomenon, namely comparative approaches and detailed studies of biotic and abiotic conditions along natural–urban gradients.
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We investigated the hypothesis that maritime climatic factors associated with summer fog and low cloud stratus (summer marine layer) help explain the compositional diversity of chaparral in the coast range of central California. We randomly sampled chaparral species composition in 0.1-hectare plots along a coast-to-interior gradient. For each plot, climatic variables were estimated and soil samples were analyzed. We used Cluster Analysis and Principle Components Analysis to objectively categorize plots into climate zone groups. Climate variables, vegetation composition and various diversity measures were compared across climate zone groups using ANOVA and nonmetric multidimensional scaling. Differences in climatic variables that relate to summer moisture availability and winter freeze events explained the majority of variance in measured conditions and coincided with three chaparral assemblages: maritime (lowland coast where the summer marine layer was strongest), transition (upland coast with mild summer marine layer influence and greater winter precipitation), and interior sites that generally lacked late summer water availability from either source. Species turnover (β-diversity) was higher among maritime and transition sites than interior sites. Coastal chaparral differs from interior chaparral in having a higher obligate seeder to facultative seeder (resprouter) ratio and by being dominated by various Arctostaphylos species as opposed to the interior dominant, Adenostoma fasciculatum. The maritime climate influence along the California central coast is associated with patterns of woody plant composition and β-diversity among sites. Summer fog in coastal lowlands and higher winter precipitation in coastal uplands combine to lower late dry season water deficit in coastal chaparral and contribute to longer fire return intervals that are associated with obligate seeders and more local endemism. Soil nutrients are comparatively less important in explaining plant community composition, but heterogeneous azonal soils contribute to local endemism and promote isolated chaparral patches within the dominant forest vegetation along the coast.
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Urban development can have multiple effects on mammalian carnivore communities. We conducted a metaanalysis of 7,929 photographs from 217 localities in 11 camera-trap studies across coastal southern California to describe habitat use and determine the effects of urban proximity (distance to urban edge) and intensity (percentage of area urbanized) on carnivore occurrence and species richness in natural habitats close to the urban boundary. Coyotes (Canis latrans) and bobcats (Lynx rufus) were distributed widely across the region. Domestic dogs (Canis lupus familiaris), striped skunks (Mephitis mephitis), raccoons (Procyon lotor), gray foxes (Urocyon cinereoargenteus), mountain lions (Puma concolor), and Virginia opossums (Didelphis virginiana) were detected less frequently, and long-tailed weasels (Mustela frenata), American badgers (Taxidea taxus), western spotted skunks (Spilogale gracilis), and domestic cats (Felis catus) were detected rarely. Habitat use generally reflected availability for most species. Coyote and raccoon occurrence increased with both proximity to and intensity of urbanization, whereas bobcat, gray fox, and mountain lion occurrence decreased with urban proximity and intensity. Domestic dogs and Virginia opossums exhibited positive and weak negative relationships, respectively, with urban intensity but were unaffected by urban proximity. Striped skunk occurrence increased with urban proximity but decreased with urban intensity. Native species richness was negatively associated with urban intensity but not urban proximity, probably because of the stronger negative response of individual species to urban intensity.
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Unlabelled: • Premise of the study: Hybridization is thought to have played an important role in diversification of the speciose shrub genus Ceanothus; putative hybrid species have been described, and data suggest that intrinsic barriers may not exist among closely related species. However, the extent to which hybridization occurs in the wild is not known, and little is understood about how extrinsic factors such as soil chemistry may influence the process. The present research focuses on the gabbro-endemic C. roderickii and the closely related soil-generalist C. cuneatus. Though the species occur peripatrically, they remain distinct across an edaphic disjunction. • Methods: AFLP was used to quantify hybridization and introgression. Biological data and experiments were used to test for prezygotic isolation. Growth trials were used to test for local adaptation and selection against hybrids. • Key results: Ceanothus cuneatus and C. roderickii were strongly differentiated morphologically and genetically, despite a lack of evidence for prezygotic barriers. Hybrids and back-crosses were present but infrequent. Finally, there was selection against hybrids in nonnative soil. • Conclusions: There is little genetic exchange between the focal species across an edaphic disjunction, despite the absence of prezygotic barriers. This result implies that soil conditions, as well as other extrinsic factors, should be considered as forces that may restrict hybridization and gene flow in Ceanothus, influencing local adaptation and speciation. Findings presented here are significant because they imply that exchange of genetic material between plants may be limited directly by the abiotic environment, rather than by the biology of the plants.
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Ione manzanita (Arctostaphylos myrtifolia) is a rare, endemic, evergreen shrub restricted to Ione formation soils (infertile, acidic, sedimentary oxisols) in the foothills of the Sierra Nevada. The widely distributed A. viscida (whiteleaf manzanita) intermixes with A. myrtifolia at the margins of Ione formation soils. In 2002, we observed extensive mortality within two mixed stands of A. myrtifolia and A. viscida near Ione, CA. At one site, nearly all plants of both species in a 0.25-ha area had died recently. At a second site, most of the A. myrtifolia and A. viscida plants on several hectares died at least 5 years earlier. Dying plants of both species exhibited wilting and desiccation of the foliage; dark brown discoloration and necrosis of the root crown, taproot, and some large roots; and loss of fine roots. Plants of all age classes were affected. We consistently isolated a Phytophthora sp. from symptomatic plants of both species using PARP (1) and acidified potato dextrose agar. We recovered the sam...
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Mammalian carnivores are particularly vulnerable to extinction in fragmented landscapes, and their disappearance may lead to increased numbers of smaller carnivores that are principle predators of birds and other small vertebrates. Such `mesopredator release' has been implicated in the decline and extinction of prey species. Because experimental manipulation of carnivores is logistically, financially and ethically problematic,, however, few studies have evaluated how trophic cascades generated by the decline of dominant predators combine with other fragmentation effects to influence species diversity in terrestrial systems. Although the mesopredator release hypothesis has received only limited critical evaluation and remains controversial, it has become the basis for conservation programmes justifying the protection of carnivores. Here we describe a study that exploits spatial and temporal variation in the distribution and abundance of an apex predator, the coyote, in a landscape fragmented by development. It appears that the decline and disappearance of the coyote, in conjunction with the effects of habitat fragmentation, affect the distribution and abundance of smaller carnivores and the persistence of their avian prey.
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Fire represents an important recruitment phase for many chaparral species. Prescribed burns are often scheduled during winter or spring when soil moisture is high in order to minimize risks of uncontrolled fire. However, chaparral wildfires typically occur in the summer or fall when soil moisture is low. Changing the seasonality of burn affects pre-burn soil moisture, burn temperature and timing of germination. High soil moisture during winter or spring burns is hypothesized to lower germination rates of chaparral plants compared to fall burns. The purpose of this study was to evaluate the effects of prescribed spring burns on the germination of chaparral species in the Mendocino National Forest, California. We conducted two experiments to test for effects of moisture on seed germination. In the soil heating experiment, soil collected under chaparral was heated at several temperatures and soil moistures, and germinating seeds were counted. In the seed heat treatment experiment, seeds of 13 species were heated moist and dry to determine the moisture effect on heated seeds. Results indicate a differential response of seeds to heat and soil moisture. Lotus humistratus, Daucus pusillus and Penstemon heterophyllus were negatively affected by temperature in both moist and dry treatments. Ceanothus cuneatus and Genista monspesullana germination increased with temperature in both dry and moist treatments. Germination of six species (Adenostoma fasciculatum, Camissonia contorta, Emmenanthe pendiflora, Epilobium ciliatum, Galium aparine and Malacothrix clevelandii) decreased under moist heat treatments. These results suggest that spring burns may lead to decreased diversity of chaparral due to reduced seed survival and germination of certain species.
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The study of interspecific variation in plant ecological strategies has revealed suites of traits associated with leaf life span and with maximum levels of water deficit (measured as leaf water potentials). Here, the relationship between these sets of traits was examined in a study of 20 co-occurring chaparral shrubs that vary in leaf habit, rooting depth, and regeneration strategies. Leaf life span (LLS) and minimum seasonal water po-tentials (min) were not significantly correlated, suggesting that they are associated with independent aspects of functional variation. Multiple regression analyses of a large suite of physiological, functional, and phenological attributes in relation to these two ''anchor traits'' supported this view. Short LLS was significantly associated with high specific leaf area, high carbon assimilation and leaf nitrogen (per mass), early onset of growth, and a multistemmed, short stature growth form. This suite of traits was also associated with opportunistic regeneration following physical disturbance. Area-based gas exchange was not tightly linked to LLS. Low min (i.e., greater water deficit) was associated with high wood density, small vessel diameters, thin twigs, low leaf area : sapwood area ratios, and early onset of leaf abscission. Among the evergreen species, this suite of traits was most characteristic of post-fire seeders, which depend on high drought tolerance for post-fire regeneration of seedlings. Plant stature was the only trait associated with both the LLS axis and the min axis of functional variation. A two-dimensional strategy space, approxi-mately defined by LLS and min , can be used to distinguish contrasting strategies of drought tolerance vs. avoidance, and alternative modes of regeneration following fire and other disturbance. This conceptual scheme illustrates the strength of a trait-based approach to defining plant strategies in relation to resource availability and disturbance.
Article
Resistance to xylem cavitation depends on the size of xylem pit membrane pores and the strength of vessels to resist collapse or, in the case of freezing-induced cavitation, conduit diameter. Altering these traits may impact plant biomechanics or water transport efficiency. The evergreen sclerophyllous shrub species, collectively referred to as chaparral, which dominate much of the mediterranean-type climate region of southern California, have been shown to display high cavitation resistance (pressure potential at 50% loss of hydraulic conductivity; P 50). We examined xylem functional and structural traits associated with more negative P 50 in stems of 26 chaparral species. We correlated raw-trait values, without phylogenetic consideration, to examine current relationships between P 50 and these xylem traits. Additionally, correlations were examined using phylogenetic independent contrasts (PICs) to determine whether evolutionary changes in these xylem traits correlate with changes in P 50 . Co-occurring chaparral species widely differ in their P 50 (À0.9 to À11.0 MPa). Species experiencing the most negative seasonal pressure potential (P min) had the highest resistance to xylem cavitation (lowest P 50). Decreased P 50 was associated with increased xylem density, stem mechanical strength (modulus of rupture), and transverse fiber wall area when both raw values and PICs were analyzed. These results support a functional and evolutionary relationship among these xylem traits and cavitation resistance. Chaparral species that do not sprout following fire but instead recruit post-fire from seed had the greatest resistance to cavitation, presumably because they rely on post-fire survival of seedlings during the summer dry period to persist in the landscape. Raw values of hydraulic vessel diameter (d h), maximum vessel length, and xylem-specific hydraulic conductivity (K s) were correlated to P 50 ; however, d h , maximum vessel length, and K s were not correlated to P 50 when analyzed using PICs, suggesting that these traits have not undergone correlated evolutionary change. We found no difference in xylem traits between species occurring at freezing vs. nonfreezing sites, although freezing has been shown to affect the survival and distributions of some chaparral species. Stem mechanical strength, fiber properties, and post-fire regeneration type appear to be key factors in the evolution of cavitation resistance among chaparral shrubs.
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At least two species of aphid, Tamalia coweni and Tamalia dicksoni (Hemiptera: Aphididae) induce galls on the leaves of Arctostaphylos spp. shrubs (Ericaceae). These galls are frequently inhabited by at least one species of congeneric inquiline. The inquiline clade has branched off from the gall-inducing clade and appears to be radiating rapidly on different host-plants, in contrast to the gall inducers. This striking pattern may offer insight into the factors driving speciation. Three key innovations present ecological opportunities for Tamalia gall-inducers and inquilines: (1) the induction of galls not only on leaf margins, but also on leaf midribs and inflorescences, both of which are novel host plant organs for Tamalia. (2) Gall-induction on well-armed host plants, otherwise protected with dense and viscous pubescence. (3) The origin of the inquiline habit in congeneric Tamalia aphids is a shift into a novel adaptive zone. Inquiline Tamalia exploit gall-inducers by competing successfully within the gall. They may have specialized along host-plant lines because of the critical need for precise timing with the plant during the gall invasion process.