Survival of the western pond turtle (Emys marmorata) in an urban California environment

The western pond turtle Emys (formerly Clemmys) marmorata is declining throughout its range, primarily due to loss of habitat via urbanization and conversion to agriculture. Urban waterways present several important challenges to freshwater turtle populations, but they also present an opportunity to maintain declining species in a ubiquitous habitat that has high public visibility. The arboretum waterway on the University of California, Davis campus is an example of an extensively altered urban habitat that supports a relatively large E. marmorata population. Over the last 6 years, we monitored the turtle population inhabiting the arboretum waterway to determine the demographic health of the population, and the challenges and opportunities that urban environments pose for pond turtles. Since 1993, the naturally existing arboretum pond turtle population has declined by approximately 40% and has shown little natural recruitment. During this time, we also introduced 31 headstarted turtles into the arboretum. Headstarting is the process of raising juveniles in captivity until they have outgrown their period of greatest vulnerability to predators, and then releasing them into the wild. Our headstarting results demonstrate that this contentious strategy is a viable option for adding young turtles to the population, although it does not address the causes of decline. Over the course of our study, we encountered nine species of non-native turtles in the waterway, and these appear to be a serious threat to the native species. As more habitat becomes urbanized, it is increasingly important to understand how freshwater turtles, such as E. marmorata, adapt to urban waterways and the impact of non-native turtles on native turtle species. Our strong feeling is that urban waterways can provide habitat for viable populations of freshwater turtles and showcase them to the public, but both the aquatic and terrestrial habitat must be managed according to the biological requirements of individual species.     

Effects of age and intensity of urbanization on farmland bird communities

Urban sprawl is now occurring worldwide and considered as a major large-scale perturbation on ecosystems. Consequently, urban territory is replacing other habitats such as agricultural areas. As farmland biotic communities are already reported to be declining, it seems necessary to assess the urbanization impact on them. We conducted a bird survey on 92 plots of 1 × 1 km chosen after stratification on the proportion of urban area and farmland habitat (either 0%, 25%, 50%, 75%), focusing on farmland habitat. Two aspects of urbanization were studied: its intensity and its age. We found that farmland bird species richness did not vary with increasing proportion of urbanized habitat. Non-farmland bird species richness increased from 0% to 25% classes and was constant for other classes. No effect of the urbanization age on farmland bird species richness was found, whereas a positive one was found on the non-farmland birds’ species richness. Abundance of the most specialized farmland birds decreases with urbanization intensity and age. We also found that, the more urbanized and the more recently urbanized the plots, the more similar bird communities. A strong difference in farmland bird’s communities’ compositions was found between 0% and 25% of urbanization, whereas no distinction was found between 50% and 75%. Altogether, our results suggest that to maintain for farmland birds, it is better to add new urban habitat in place where it already exist, rather than to spread it in small lots throughout the landscape.     

Effects of Key deer herbivory on forest communities in the lower Florida Keys

Ungulate herbivory can have strong impacts on plant communities, but these impacts are rarely considered in recovery plans of endangered species. This study examined the effects of the endangered Key deer (Odocoileus virginianus clavium) on its environment in the lower Florida Keys. The Key deer population has increased to over 700 deer from approximately 50 deer in the 1950s; however, approximately 75% of the population resides on only a few islands (Big Pine, No Name, Big Munson) where Key deer herbivory on forest communities may be substantial. Effects of deer herbivory on plant densities were estimated on these islands using vegetation quadrats in hardwood hammock, buttonwood transition, and mangrove wetlands and compared to nine other islands with intermediate or low deer densities. On islands with high deer density, densities of preferred woody plant species <1.2 m tall (within Key deer reach) were significantly lower than islands with lower deer densities, while densities of some nonpreferred species were significantly higher. Deer exclosures established in hardwood hammock on a high-density deer island revealed a mean increase in abundance/height of preferred woody species inside exclosures, while nonpreferred species significantly increased in open plots. We conclude that on high deer density islands, highly preferred plant species might eventually fail to regenerate and unpalatable plant species may become dominant. Careful criteria need to be developed to maintain Key deer numbers above an endangered species status yet below levels that are destructive to local forest species.     

Browsing down our natural heritage: Deer impacts on vegetation structure and songbird populations across an island archipelago

Declines in forest and woodland birds have largely been attributed to habitat loss and fragmentation. In the past decade, however, the potential for herbivores to influence bird species abundance and community composition via their direct impact on vegetation structure has also been recognised. We tested the hypothesis that deer influence vegetation structure and bird assemblages in a large island archipelago in western North America using surveys of 18 islands with deer densities ranging from 0 to over 1 deer/ha. Amongst these islands, reduced predation and hunting pressure has allowed deer populations to increase above those likely to have existed in pre-European times. Our results support a growing body of evidence that deer regulate both the cover and architecture of understory vegetation which in turn profoundly affects island bird assemblages. Deer-free islands supported the most abundant and diverse bird fauna. Iconic songbirds such as the rufous hummingbird, song and fox sparrow were abundant on islands with no deer but substantially reduced on islands with high deer densities. Only one bird species, the dark-eyed junco, preferred moderate and high density deer islands. Our observations suggest that current cohorts of palatable shrubs on islands with high deer densities are relatively old and potentially represent an impending extinction debt, where the full effects of high deer density on island biota may take decades to fully unfold. Our results suggest that deer densities below a threshold of 0.1 deer/ha should allow native vegetation to recover and a rich and diverse bird species assemblage to persist. We suggest that adaptive management be used to test the validity of this threshold, and that without active management of deer abundance, local extinctions of native flora and fauna appear likely to accelerate.     

Effects of community-level grassland management on the non-target rare annual Agalinis auriculata

The objective of grassland management is to maintain keystone species, as well as species diversity, to promote a particular community structure, or to preserve specific ecosystem processes. Studies of grassland management rarely ascertain the effects on rare plant species, although conservation plans for rare herbaceous plants often recommend habitat management as well as restoration activities. Indeed, conservation biology has evolved from a relatively species-specific discipline into one more focused on larger scale issues such as ecosystem function, community composition and habitat restoration. Few studies have tested whether species of concern are adequately managed with a community or ecosystem-level approach. In this study, we evaluate whether community-level management of white-tailed deer and woody brush improves the viability of the rare annual plant species, Agalinis auriculata (Earleaf false foxglove; Orobanchaceae). Reducing deer browse and removing brush each positively affect plant vital rates. Brush removal increases the proportion of plants that reach the largest size class. Reducing deer browse increases the fertility of plants, particularly those in the largest size class. We report on demographic matrix models created with data from five populations of A. auriculata studied across 4 years. We find that both management activities positively affect the non-target plant species and are, in fact, necessary for A. auriculata to persist. Conservation of A. auriculata at our study sites requires both reducing the density of white-tailed deer and brush removal. Our study demonstrates that management at the community and ecosystem levels can be compatible with conservation goals at the species and population levels.     

The implications of current and future urbanization for global protected areas and biodiversity conservation

Due to human population growth and migration, there will be nearly 2 billion new urban residents by 2030, yet the consequences of both current and future urbanization for biodiversity conservation are poorly known. Here we show that urban growth will have impacts on ecoregions, rare species, and protected areas that are localized but cumulatively significant. Currently, 29 of the world’s 825 ecoregions have over one-third of their area urbanized, and these 29 ecoregions are the only home of 213 endemic terrestrial vertebrate species. Our analyses suggest that 8% of terrestrial vertebrate species on the IUCN Red List are imperiled largely because of urban development. By 2030, 15 additional ecoregions are expected to lose more than 5% of their remaining undeveloped area, and they contain 118 vertebrate species found nowhere else. Of the 779 rare species with only one known population globally, 24 are expected to be impacted by urban growth. In addition, the distance between protected areas and cities is predicted to shrink dramatically in some regions: for example, the median distance from a protected area to a city in Eastern Asia is predicted to fall from 43 km to 23 km by 2030. Most protected areas likely to be impacted by new urban growth (88%) are in countries of low to moderate income, potentially limiting institutional capacity to adapt to new anthropogenic stresses on protected areas. In short, trends in global ecoregions, rare species, and protected areas suggest localized but significant biodiversity degradation associated with current and upcoming urbanization.     

Spatial and temporal variation in the Argentine ant edge effect: Implications for the mechanism of edge limitation

One consequence of human land-use is the exposure of native communities to invasive human commensal species along edges. Argentine ants (Linepithema humile) invade a variety of habitats in California with consequent dramatic declines in native ants. In coastal southern California, USA Argentine ants appear to be an edge effect in small habitat fragments [Suarez, A.V., Bolger, D.T., Case, T.J., 1998. Effects of fragmentation and invasion on native ant communities in coastal southern California. Ecology 79, 2041-2056]. They invade fragments from the urban edge, but only penetrate coastal sage scrub (CSS) habitat to a distance of approximately 200 m. Using pitfall sampling in edge (<250 m from the urban edge) and interior (>600 m from the edge) habitat I tested whether there is also an Argentine ant edge effect in the largest blocks of habitat in the landscape and investigated patterns of spatial and temporal variation in native and Argentine ants. Argentine ants were common in coastal sage scrub habitat within 250 m of urban edges, but rare in interior areas. Correspondingly, native ants were significantly less abundant and diverse in edge areas as compared to interior. Over the period 1997-2000 Argentine ants did not become more abundant in interior habitat suggesting it will remain a refuge for native ants. Argentine ant abundance in edge plots varied greatly among years and sites. Annual variation in abundance was positively related to annual rainfall. Increased soil moisture near edges due to urban runoff has often been suggested as the mechanism that allows the invasion of edge but not interior habitat. This hypothesis predicts that edge habitat downslope of the urban edge should support invasions of higher abundance and greater spatial penetration than habitat upslope. However, I found that edge slope did not predict the extent of invasion, whereas, soil type did. Coarse, well-drained soils supported an Argentine ant invasion of lower abundance and lesser spatial penetration than soils that should retain more moisture. These patterns of spatial and annual variation are more consistent with a biotic flow mechanism where ants move from urban habitat into CSS sites that are temporarily favorable, rather than an abiotic flow where urban runoff causes a physical change to CSS habitat near edges. This invasion affects a substantial area of habitat, however, the inability of Argentine ants to invade interior habitat suggests that refugia for native ants will persist if large unfragmented blocks of habitat are maintained.     

Predator control for protecting kaki (Himantopus novaezelandiae)—lessons from 20 years of management

In New Zealand, the endemic kaki or black stilt (Himantopus novaezelandiae) has been the focus of intensive conservation management for the past 20 years. Threatened by predation and habitat loss, the population fell to as low as 23 birds before management was implemented to reverse the decline. Predator trapping has been one form of management intervention in the wild, yet despite 20 years of control, there is only limited evidence to suggest that predator trapping is beneficial for the survival of kaki. Lack of adequate experimental design and understanding of the predator-prey dynamics in the system in which kaki live appear to be the main reasons why the benefits of predator control are not consistently clear. An adaptive management approach would have provided more information on the efficacy of predator trapping and increased understanding of the inter-relationships between kaki survival and predator abundance.     

Dynamic wildlife habitat models: Seasonal foods and mortality risk predict occupancy-abundance and habitat selection in grizzly bears

Most current wildlife habitat models, such as resource selection functions, typically assume a static environment, extrapolate poorly in space and time, and often lack linkages to population processes. We submit that more mechanistic habitat models that directly consider bottom-up resources affecting growth and reproduction (i.e., food) and top-down limitations affecting survival are needed to effectively predict habitat quality, especially in the presence of rapid environmental change. Here we present a general model for estimating potential habitat quality (relating to growth and reproduction) and realised habitat quality (accounting for survival) using basic knowledge of the species’ seasonal diet, predicted locations of food resource patches and regional patterns in mortality risk. We illustrate our model for a threatened population of grizzly bears in west-central Alberta. Bi-monthly potential habitat quality successfully predicted habitat selection by radio-collared grizzly bears, while multi-seasonal realised habitat quality predicted patterns in occupancy-abundance as measured from unique bears at hair-snag sites. Bottom-up resources therefore predicted patterns of habitat selection, while top-down processes (survival) were necessary to scale-up to population measures. We suggest that more direct measures of resources and environments that affect growth, reproduction and survival, as well as match the temporal scale of animal behaviour, be considered when developing wildlife habitat models.     

Extirpation, colonization, and habitat dynamics of a keystone species along an urban gradient

Using 5 years of patch occupancy data for 384 habitat fragments, we evaluated population and habitat dynamics of the black-tailed prairie dog in urban habitat remnants in the rapidly developing landscape of Denver, CO, USA. Specifically, we evaluated the landscape factors, including fragment area, age, and connectivity, that characterize the habitat fragments most likely to be colonized by prairie dogs, as well as those experiencing local extinctions. In addition, we determined which patch types were most often removed by land development. Sites in proximity to colonies were more likely to be colonized by prairie dogs. Local extinctions were most common on isolated colonies, and older and more isolated colonies were more likely to be extirpated by human activity. In general, smaller and older habitat patches were at the highest risk of being lost to land development. Our results provide observations of dynamic changes to the distribution of a potential keystone species in an urban area, which can be used to inform island biogeographic and metapopulation models for wildlife persistence in developing landscapes. Although populations are currently in decline, most local extinctions are the direct result of human activity, and we suggest that prairie dogs in this area can persist with appropriate management.     

江西省1988-2017年新型城镇化水平与不透水面的相关关系

[目的] 结合不透水面对新型城镇化水平进行分析，探究江西省各市新型城镇化发展的规律及趋势，为江西省新型城镇化的发展提供科学参考。[方法] 从人口、经济、社会、空间4个方面构建新型城镇化的指标体系，在分析江西省1988-2017年各市新型城镇化水平的同时，基于不透水面数据，研究城镇化水平与不透水面不同阶段的相关性变化，构建二者的线性关系模型。[结果] ①30 a间江西省城镇不透水面扩张明显，整体呈现高-较高-中-较低-低密度圈层分布的空间格局。②江西省城镇化发展水平呈现出"北高南低"的空间分布特征，区域间发展不均衡；③2006年为该区城镇化水平增长的突变点，前后城镇化水平与不透水面相关性存在差异；④各市不透水面与新型城镇化水平线性拟合决定系数R²均大于0.9，拟合效果较好。[结论] 不透水面与新型城镇化水平存在较强相关性，利用不透水面数据能较好地反映各市新型城镇化水平，这有助于分析城镇化发展趋势，促进区域城镇化研究。     

Two genetically distinct units of the Chinese sika deer (cervus nippon): analyses of mitochondrial DNA variation

Chinese sika deer, Cervus nippon, are currently threatened by habitat loss, fragmentation and human hunting, which has led to the extinction of three subspecies in the wild. The remaining subspecies subsist in the narrow regions of Jilin, Heilongjiang, Sichuan, Gansu, Jiangxi, Anhui, and Zhejiang provinces. In order to design effective conservation strategies for the Chinese sika deer, we have investigated genetic diversity, population structure and gene flow in the Chinese sika deer populations by analyzing ≈995 base pairs of the mitochondrial DNA (mtDNA) control region in 59 individuals sampled from the northeast of China, Sichuan, Jiangxi and Zhejiang. Chinese sika deer exhibited low mtDNA diversity and high gene flow among the four populations, and showed no strong geographical structure. The analyses of mtDNA variation among individuals of sika deer identified only two main phylogenetic groups even though three subspecies were sampled. These data singles out the Zhejiang population as being highly genetically distinct and worthy of separate conservation consideration. Therefore, it is recommended that a breeding program for the Zhejiang population be established.     

Landscape effects on black-tailed prairie dog colonies

Black-tailed prairie dogs (Cynomys ludovicianus) increasingly compete for available habitat with human development in the Colorado Front Range. Because the effects of increased urbanization on prairie dog colonies are unknown, we studied how landscape context affects prairie dog density in Boulder County, Colorado, USA. We used burrow density as a proxy for prairie dog density because these variables were correlated at our study sites (r=0.60). Using remotely sensed data and a GIS, we quantified percent urbanization, road density, and the percentage of other prairie dog colonies in the surrounding landscape at 200, 1000, and 2000 m from the perimeter of 22 prairie dog colonies, and compared burrow density with each landscape variable at each scale. We also calculated Akaike's information criterion (AIC) to determine the most parsimonious models predicting burrow density. Ranges of burrow densities and prairie dog densities in Boulder County were higher than in other studies using similar methodology. Within Boulder County, burrow density was significantly higher in colonies surrounded by greater density of roads. The degree to which prairie dog colonies were immediately surrounded by unsuitable habitat, i.e. the “boundedness” of the colony, was negatively correlated with colony area and positively correlated with burrow density. A model based on boundedness, the density of roads at the 2000 m scale, and the amount of prairie dog colonies at the 200 m scale explained 73% of the variance in prairie dog burrow density. However, a non-linear model including boundedness and the squared term of road density at the 2000 m scale had the lowest AIC value of all linear and non-linear models, indicating a possible threshold effect of urbanization on prairie dog density. Urbanization may have several implications for prairie dog persistence. Increased prairie dog density in urbanized landscapes may be related to the Refuge effect, i.e. decreased predator abundance. If higher prairie dog density increases competition for available resources, habitat quality may decline leading to population decline in highly urbanized landscapes. Furthermore, if dispersal is reduced in urbanized landscapes, then these colonies may not be recolonized after local extirpation from plague epizootics. Alternatively, urbanized colonies may be effectively isolated from plague vectors and reservoir hosts, which could result in a lower frequency of plague epizootics when compared to non-urbanized colonies.     

Pampas deer conservation with respect to habitat loss and protected area considerations in San Luis, Argentina

Ozotoceros bezoarticus celer is the most endangered subspecies of pampas deer. Although common in the Argentine Pampas 100 years ago, it persists in only two small populations. The largest population has survived due to the rarity of roads, internal farm subdivisions, and the low cattle density. However, habitat condition for this population has changed dramatically in the last 16 years. Five Landsat images (1985, 1992, 1997, 1999, 2001), covering 4608 km², were used to quantify pampas deer habitat loss due to the replacement of natural grassland by exotic pastures and crops. Image classification showed that natural grassland cover was reduced from 84.5 to 37.8% between 1985 and 2001. The annual transformation rate increased significantly from 1.4 to 10.9%. Average paddock size was significantly reduced from 1470 to 873 ha, and the number of paddocks increased from 129 to 227. The land within this area proposed for a national park has not escaped these habitat changes. In the last 6 years the amount of replaced area within the proposed park has increased from 9.1 to 51.1% due to actions by ranchers to avoid inclusion within park boundaries. Three patches of natural grassland still remain within the pampas deer distribution, one of which is the proposed national park. The implementation of a national park is a decisive challenge for the survival of pampas deer and its habitat in Argentina.     

深圳城市化水土流失整治中的生态建设问题探讨

论述了我国城市化加快发展的必然趋势,分析了城市化过程中可能出现的水土流失形式及其危害。并以深圳市为典型案例,探讨了城市水土流失整治中城市生态重建的有关问题。提出按城市发展轴线、河道、建成区类型和填海造地开发区等类型分别采取相应的生态重建对策。     

Three decades of urbanization: Estimating the impact of land-cover change on stream salamander populations

Urbanization has become the dominant form of landscape disturbance in parts of the United States. Small streams in the Piedmont region of the eastern United States support high densities of salamanders and are often the first habitats to be affected by landscape-altering factors such as urbanization. We used US Geological Survey land cover data from 1972 to 2000 and a relation between stream salamanders and land cover, established from recent research, to estimate the impact of contemporary land-cover change on the abundance of stream salamanders near Davidson, North Carolina, a Piedmont locale that has experienced rapid urbanization during this time. Our analysis indicates that southern two-lined salamander (Eurycea cirrigera) populations have decreased from 32% to 44% while northern dusky salamanders (Desmognathus fuscus) have decreased from 21% to 30% over the last three decades. Our results suggest that the widespread conversion of forest to urban land in small catchments has likely resulted in a substantial decline of populations of stream salamanders and could have serious effects on stream ecosystems.     

近30年来城市化进程对北京区域气温的影响

分析了20世纪70年代以来北京市气温指数的变化规律,发现其与城市化进程有良好对应关系。并应用主成分分析方法,将影响北京城区及郊县各站气温变化的因子分为区域因子及局地因子。计算表明,城市化带来的热岛效应是导致局地增暖的主要因子,占总增暖比重的47.5%～61.2%。在众多表征城市发展的指标中,气温与人口总量的相关性最好。以上结果有助于深入探讨城市化对区域气候的影响机制。     

Using habitat models to determine conservation priorities for pond-breeding amphibians in a privately-owned landscape of northern Idaho, USA

As rural landscapes experience increasing levels of residential development, the persistence of species that rely on them will depend on informed planning and management decisions. An understanding of habitat requirements is essential for setting priorities and developing landscape-level plans for the survival of these species. In many temperate rural landscapes, artificially created ponds may be the only wetlands available for aquatic reproduction by amphibians. The introduction of non-native fish into these ponds reduces survival and prohibits successful reproduction of many native pond-breeding amphibians. We surveyed 105 randomly selected wetlands in a primarily privately-owned, rural landscape in north Idaho, USA, for pond-breeding amphibian larvae in 2004 and 2005. We used an information theoretic multimodel inference and an algorithmic (random forests) approach to model habitat for each species based on local and landscape characteristics. We also used a mail survey to quantify how landowners value fish in their wetlands and their plans for future wetland development and fish stocking. Sixty-seven percent of pond owners reported that fishing in their pond was at least slightly important to them and 36% of owners indicated that they were at least 50% likely to add fish to their ponds in the next 5-10 years. Landscape change predictions for this area indicate that forests will become more open due to thinning; habitat models indicated that this is likely to be detrimental to long-toed salamanders and beneficial to Pacific treefrogs. Habitat models also indicate that Columbia spotted frog breeding sites consist of wetlands on flat ground with high solar insolation and that this species is sensitive to nearby development, indicating that as this landscape becomes further developed, this species may require habitat protection for persistence.     

乌鲁木齐市城市化进程与耕地面积变化的定量研究

耕地是人类赖以生存的基本条件,随着城市化水平不断发展,耕地与建设用地之间的矛盾日益突出。如何协调城市化发展与耕地面积减少之间的矛盾是当前亟待解决的问题。该文以乌鲁木齐市为例,建立城市化水平评价指标体系,运用相关分析和回归分析方法对乌鲁木齐城市化水平与耕地面积的关系进行定量研究。研究表明,1999-2006年乌鲁木齐市城市化水平与耕地面积之间相关系数为0.229,呈现弱相关关系;1999-2004年其相关系数为-0.952,存在强负相关性。     

Use of monitoring data and population viability analysis to inform reintroduction decisions: Peregrine falcons in the Midwestern United States

The peregrine falcon (Falco peregrinus anatum) has not yet recolonized natural cliff sites in Illinois and much of the lower Midwestern US, and remains restricted to urban areas. We constructed a landscape-linked population viability analysis using RAMAS/GIS software to compare possible reintroduction strategies for the species. Habitat-specific (i.e. cliff and urban) demographic parameters such as survival, fecundity, and dispersal rates were derived from the Midwest Peregrine Society Database for peregrines in the central Mississippi River region during 1982-2006. We simulated a base scenario of no reintroduction and 18 models of reintroduction with varying cohort sizes, supplementation schedules, and number of reintroduction sites, and used the Lake Superior population to test our model. Our analysis indicated that even without reintroductions in Illinois, the peregrine population in the lower Midwestern region is slowly increasing and is not likely to go extinct. Recolonization of cliff sites in southern Illinois likely will occur via dispersal from urban populations, however further research on dispersal rates between urban areas and cliffs is needed. Analysis indicated that the most cost-effective reintroduction strategy would be priced at approximately $280,000 and would result in only two additional breeding pairs compared to the no-action scenario. Thus, funds would be more effectively used in other management efforts such as habitat preservation. This study provides an example of how post-release monitoring can be used to inform future reintroduction plans.