Picture worth a thousand words: Updating repeat photography for 21st century ecologists

1. Anthropogenic climate change is altering every ecosystem on Earth. Understanding these changes requires quality baseline measurements of ecosystem states. While satellite imagery provides a coarse baseline for regional‐scale changes in vegetation, landscape‐scale observations are lacking. Ground‐based repeat photographic points (RPP) can provide this finer baseline. As precise visual records of ecosystems at a particular time, RPP provide rich data for diverse uses. Current methodology for establishing RPP, developed in the era of film cameras, requires placement of permanent markers in a landscape to provide accurate repeats over time. Another form of RPP involves relocating sites of historic photographs, to assess change between historic and present‐day photographs. Through a three‐year field survey, we synthesized these techniques to modernize repeat photography for the 21st century ecologist.
2. We established 100 RPP in the Peloncillo Mountains of New Mexico, recapturing 86 RPP in the three years (2015–2017) of the study. During our study, a large (>16,000 ha) complex of wildfires burned more than half of the RPP sites we established in the prior month, providing a unique opportunity to assess method accuracy after dramatic landscape disturbance by comparing burned, unburned, pre‐, and post‐fire RPP image recapture precision.
3. Our method produced 92% mean similarity for 86 RPP between original and repeated photographs, with no difference between burned and unburned sites. Interval between photographs did not cause a decline in similarity.
4. Our updated methods can be practically applied to nearly all terrestrial study systems. Landscape changes driven by human (e.g., effects of anthropogenic climate change, land use) and natural activities (e.g., wildfires, phenology, and hydrologic events) are especially well suited to our updated methods. Modern smartphones include the technology necessary (e.g., camera, GPS, and compass) to employ our method and provide a means for low‐cost deployment of the technique in diverse landscapes. We encourage broad adoption of this technique to establish baseline RPP of ecosystems across the globe, and the formation of a centralized database for repeat photography.

     

黄土高原人口密集区城镇扩张对生境质量的影响——以兰州、西安-咸阳及太原为例

快速城镇化过程极大改变了区域生境的空间格局和功能要素,深刻影响生境斑块之间的物质流和能量流,同时对生境和生物多样性造成严重威胁。本研究采用InVEST模型、景观指数及多元线性回归,系统分析了1990—2018年黄土高原全域及人口密集区城镇化对生境质量影响的时空格局特征与因素。结果表明: 黄土高原城镇扩张显著影响生境质量,1990—2018年间建设用地面积增幅49.6%,导致生境斑块的总面积减少5.2%。2010年后,城镇斑块面积上升,斑块密度和破碎度下降,使城镇生境质量呈现出“外高中低”的空间格局。人口密集区城镇扩张速率与生境质量呈现显著负相关,区域内生境质量平均值下降2.7%,生境退化水平上升33.4%。生境质量等级不稳定,高等级生境易转为低一等级,兰州、西安-咸阳和太原转化率分别为12.9%、2.9%和1.7%。本研究所用8个影响因素能有效解释生境质量的空间变化(R²=68.7%),其中,人口密度和距道路距离是导致生境破碎化的主要因素,坡度、GDP及降水对生境空间格局优化具有积极作用。     

Use of sand wave habitats by silver hake

Silver hake Merluccius bilinearis are common members of fish communities in sand wave habitats on Georges Bank and on Stellwagen Bank in the Gulf of Maine. Observations of fish size v . sand wave period showed that silver hake are not randomly distributed within sand wave landscapes. Regression analyses showed a significant positive relationship between sand wave period and fish length. Correlation coefficients, however, were low, suggesting other interactions with sand wave morphology, the range of current velocities, and available prey may also influence their distribution. Direct contact with sand wave habitats varied over diel periods, with more fish resting on the seafloor during daytime than at night. Social foraging, in the form of polarized groups of fish swimming in linear formations during crepuscular and daytime periods, was also observed. Sand wave habitats may provide shelter from current flows and mediate fish–prey interactions.     

Restoration for variability: emergence of the habitat diversity paradigm in terrestrial ecosystem restoration

Ecosystem restoration implies focusing on multiple trophic levels and ecosystem functioning, yet higher trophic levels, that is, animals, are less frequently targeted by restoration than plants. Habitat diversity, the spatial heterogeneity between and within habitat patches in a landscape, is a well‐known driver of species diversity, and offers possible ways to increase species diversity at multiple trophic levels. We argue that habitat diversity is central in whole‐ecosystem restoration as we review its importance, provide a practical definition for its components, and propose ways to target it in restoration. Restoration targeting habitat diversity is used commonly in aquatic ecosystems, mostly to increase the physical diversity of habitats, meant to provide more niches available to a higher number of animal species. To facilitate the uptake of habitat diversity in terrestrial ecosystem restoration, we distinguish between compositional and structural habitat diversity, because different animal groups will respond to different aspects of habitat diversity. We also propose four methods to increase habitat diversity: varying the starting conditions to obtain divergent successional pathways, emulating natural disturbances, establishing keystone structures, and applying ecosystem engineer species. We provide two case studies to illustrate how these components and methods can be incorporated in restoration. We conclude that targeting habitat diversity is a promising way to restore habitats for a multitude of species of animals and plants, and that it should become mainstream in restoration ecology and practice. We encourage the restoration community to consider compositional and structural habitat diversity and to specifically target habitat diversity in ecosystem restoration.     

Assessment of spatial genetic structure to identify populations at risk for infection of an emerging epizootic disease

1. Understanding the geographic extent and connectivity of wildlife populations can provide important insights into the management of disease outbreaks but defining patterns of population structure is difficult for widely distributed species. Landscape genetic analyses are powerful methods for identifying cryptic structure and movement patterns that may be associated with spatial epizootic patterns in such cases.
2. We characterized patterns of population substructure and connectivity using microsatellite genotypes from 2,222 white‐tailed deer (Odocoileus virginianus) in the Mid‐Atlantic region of the United States, a region where chronic wasting disease was first detected in 2009. The goal of this study was to evaluate the juxtaposition between population structure, landscape features that influence gene flow, and current disease management units.
3. Clustering analyses identified four to five subpopulations in this region, the edges of which corresponded to ecophysiographic provinces. Subpopulations were further partitioned into 11 clusters with subtle (F_ST ≤ 0.041), but significant genetic differentiation. Genetic differentiation was lower and migration rates were higher among neighboring genetic clusters, indicating an underlying genetic cline. Genetic discontinuities were associated with topographic barriers, however.
4. Resistance surface modeling indicated that gene flow was diffuse in homogenous landscapes, but the direction and extent of gene flow were influenced by forest cover, traffic volume, and elevational relief in subregions heterogeneous for these landscape features. Chronic wasting disease primarily occurred among genetic clusters within a single subpopulation and along corridors of high landscape connectivity.
5. These results may suggest a possible correlation between population substructure, landscape connectivity, and the occurrence of diseases for widespread species. Considering these factors may be useful in delineating effective management units, although only the largest features produced appreciable differences in subpopulation structure. Disease mitigation strategies implemented at the scale of ecophysiographic provinces are likely to be more effective than those implemented at finer scales.

     

Diversity and abundance of insect visitors to flowers of trees and shrubs in a South African savannah

This study presents the results of a landscape‐scale survey for insect floral visitors in the Skukuza Ranger District, Kruger National Park, South Africa. Floral visitors were sampled from flowering trees and shrubs along linear transects spanning the entire district. Six plant species were sampled in the late dry season (Acacia grandicornuta Gerstner, A. nigrescens Oliver, Cassia abbreviata Oliver, Combretum hereroense Schinz, Combretum zeyheri Sonder, Euclea divonorum Hiern), and eleven plant species were sampled during the rainy season (Acacia exuvialis Verdcourt, A. grandicornuta Gerstner, A. nilotica (L.) Willdenow, A. tortilis (Forsskal) Hayne, Dichrostachys cinerea Miquel, Flueggea virosa (Roxburgh) Baillon, Grewia bicolor Jussieu, G. flava De Candolle, G. flavescens Jussieu, G. monticola Sonder, and Peltophorum africanum Sonder). Coleoptera, Hymenoptera and Lepidoptera comprised the majority of floral visitors, while species of Blattodea, Diptera, Hemiptera and Neuroptera also occurred on flowers. Known or likely pollinators include bees (Hymenoptera: Apidae, Halictidae and Megachilidae) and scarab beetles (Coleoptera: Scarabaeidae). These plant species appear to have generalist pollination systems, with the exception of species of Grewia L., which appear to be pollinated primarily by bees. A provisional plant–pollinator food web is presented for the eleven species of trees and shrubs which flower during the rainy season.