The Reeuwijk lakes: A five years water quality study in an eutrophic ecosystem

The Reeuwijk Lakes (The Netherlands) present a typical example of eutrophication in the lower Rhine catchment area. In 1986 restoration of these lakes started by reducing the external P-loading. Two lakes, Lake Elfhoeven and Lake Nieuwenbroek, differing in P-load and residence time were selected for monitoring water quality parameters before (1983–1985) and after (1986–1987) these restoration measures. Reduction of the external P-loading did not result in lower P-concentrations in both lakes. In contrast, P and N increased. This may have been caused by an increase in diffuse discharges. However, seasonal cycles of P and N point to a strong internal loading of nutrients. The concentrations of chlorophyll a and carotene decreased, indicating a lower phytoplankton biomass. However, as C-phycocyanine concentrations increased the relative abundance of cyanobacteria became higher. Seston concentrations and zooplankton densities did not change. Transparency in the lakes slightly decreased after P-reduction and is far too low for the development of any vegetation of submerged waterplants. The typical differences between both lakes remained after restoration measures. The inverse relationship between the concentrations of chlorophyll a and total phosphorus at the two sampled stations remained constant. The differences in phytoplankton composition and the zooplankton biomass give a plausible explanation for this inverse relationship, between the two stations. Restoring the lakes after four decades of P-loading can presumably, not simply be done by lowering the external P-load alone. Supplementary in-lake measures may accelerate the restoration process.     

演替理论与植被恢复

《昆明-蒙特利尔全球生物多样性框架》提出要高质量保护和恢复各30%的土地,最大化地实现保护生物多样性和缓解气候变化的目标,而演替理论和植被恢复可以为实现30%的保护和恢复目标服务。演替理论是植被生态学中的核心理论,演替是指在一个地点上由一群不同物种组成的生命体的结构或组成随时间而变化的过程; 植被恢复是以植物种植、配置为主,恢复或重建植物群落或天然更新恢复植物群落的过程,植被恢复是生态系统结构和功能从简单到复杂、从低级向高级变化的过程,最终目的是建立健康稳定的植物群落。演替是植被恢复的基础,植被恢复被视为对演替过程的操纵,以达到恢复受损植被生态系统的目标。演替理论可以指导植被恢复,而植被恢复对演替理论的发展有益。演替按裸地性质可以分为原生演替和次生演替,有研究建议将恢复过程视为第三演替,这将有助于理解通过人为干预促进植被恢复成功的管理选择,特别是通过强调退化生态系统中的环境和生物遗存的管理选择。此外,该文还提出了植被恢复理论和演替理论未来可能重点关注的科学和技术问题。     

The Restoration of Elk (Cervus elaphus) in Ontario, Canada: 1998–2005

In 1997, a plan to restore Elk (Cervus elaphus) to Ontario was approved by the provincial government. The objective of the Ontario elk restoration program, a multipartnered collaboration, was to restore a species that had been extirpated from the province during the 1800s. During 1998–2001, 460 elk were acquired from Elk Island National Park, Alberta, for release in four areas of Ontario. As greater than 90% of the elk were radio collared, monitoring provided detailed information on the dynamics of the four populations. Comprehensive research projects using graduate students were implemented to determine the environmental impact of releasing elk in Ontario. Those studies are in progress or have been completed and include the effect of wolf predation on restored elk, white‐tailed deer and elk resource overlap, the development of genetic profiles for elk, and solutions for elk/human conflicts. Mortality of the released elk averaged 41% (190/460) during 1998–2004 with annual mortality generally declining over time in each release area. The primary causes of elk mortality included wolf predation (25% of mortalities), illegal shooting (13%), stress‐related emaciation (13%) (partially due to the stress of relocation), bacterial infections (7%), and collisions with vehicles (6%). Productivity has been high in one of the release areas with 24–65% of the cows being observed with calves during late winter surveys. However, productivity has been low in two of the northern release areas due to a variety of factors including wolf predation. In some areas, dispersion of elk appeared to be related to the length of time animals were kept in pens prior to release. The precalving population estimate for Ontario in March 2004 was 375–440 elk. A comprehensive program review was conducted in 2003/2004 that included recommendations relating to the future management of elk in Ontario.     

Developing strategies and methods for rehabilitating degraded pastures using native grasses

Summary   The purpose of this comment paper is to highlight the need for more research that aims to develop strategies and methods for establishing and maintaining native grasses in degraded pastures. Clues to finding the best strategies are linked to the vigorous debate concerning the relationship between biodiversity and ecosystem function, which has resonated in ecological research for more than 20 years. Studies aimed at investigating the operational validity of the 'sampling effect' hypothesis vs. the 'niche complementarity' hypothesis could provide valuable direction on how to successfully re-establish healthy and stable native pasture communities, including the number of species and functional groups needed. Once strategies have been developed, then practical methods on grazing management and sowing are also needed. In the long run, research initiatives in this direction could act to benefit the conservation of native grass diversity, while at the same time, sustain important ecological (and economic) functions such as production, nutrient cycling and resistance to invasion.     

Short-Term Temporal Effects on Community Structure of Lepidoptera in Restored and Remnant Tallgrass Prairies

Understanding the degree to which species assemblages naturally vary over time will be critically important when assessing whether direct management effects or contingency is responsible for species gain or loss. In this study, we tested three predictions related to short‐term variation in prairie moth communities: (1) communities would only exhibit significant temporal variation in newly restored sites (1–3 years old); (2) prairie size and age would positively influence community reassembly, with larger, older restorations sampling a greater proportion of the regional species pool; and (3) older restorations (7–10 years old) would have yet to converge on the community composition of prairie remnants. Moths were sampled from 13 Tallgrass prairie restorations and remnants in central Iowa in 2004–2005. Repeated measures analysis of variance revealed significant effects of sampling year on moth species richness and abundance as well as on the richness of two functional groups, but difference among prairie types was only observed in 2005. Rarefaction analysis revealed that older restorations and prairie remnants supported higher species richness compared to recently planted sites, and nonmetric, multidimensional scaling ordination indicated that restorations older than 7 years were clearly converging on the species composition of remnants. These results suggest that moth communities in restorations and remnants are highly variable in time but that as restorations age, they appear to reaccumulate moth species found in prairie remnants. The long‐term persistence of a particular species assemblage within a given site, however, might be a difficult endpoint to attain in central Iowa prairies because of significant annual variation in species occurrence.     

Diversity, endemism and species turnover of millipedes within the south-western Australian global biodiversity hotspot

Aim To examine how current and historical environmental gradients affect patterns of millipede (Diplopoda) endemism and species turnover in a global hotspot of floristic diversity, and to identify regions of high endemism and taxonomic distinctness for conservation management. Location South‐western Australia. Methods Museum database records of millipedes (subclasses Pentazonia and Helminthomorpha), supplemented with extensive fieldwork, were used to map species richness, species turnover (β‐diversity), weighted endemism, average taxonomic distinctness and variation in taxonomic distinctness in half‐degree grid squares (c. 2500 km²). Generalized linear models were used to examine relationships between these parameters with rainfall (present day and historical), topography and human disturbance (clearing for agriculture and urbanization). Results Millipede species richness, particularly within the order Spirostreptida, and millipede endemism were positively associated with large within‐cell differences in elevation (mountainous regions). Large variation in taxonomic distinctness (unevenness in the taxonomic tree) in higher‐rainfall areas was mainly due to speciation within the Spirostreptida genus Atelomastix. Hotspots of millipede endemism and taxonomic distinctness were identified within three categories of importance: primary (Stirling Range East, Cape Le Grand, Cape Arid, Walpole, Porongurups), secondary (Mount Manypeaks, Bremer Bay, Stirling Range West, Duke of Orleans Bay, Ravensthorpe, Albany, Busselton) and tertiary (Nornalup). A species turnover boundary was positively associated with rainfall, broadly located in the transition zone of 300–600 mm year^?1. Main conclusions The current lack of knowledge on the endemism of invertebrates hampers their incorporation into conservation planning. With this knowledge we can identify global biodiversity hotspots and, at a smaller scale, significant conservation areas within a region. Here we have shown that weighted endemism and taxonomic distinctness are useful tools in identifying centres of high endemism and speciation for millipedes within the south‐west Australian hotspot. Moreover, it is unlikely that either vertebrates or vascular plants will be useful surrogates for identifying significant areas for invertebrate conservation. While other workers have shown that vascular plants, mammals and frogs have different centres of endemism within south‐west Australia, our results show that centres of endemism for millipedes encompass all of these plus other areas.     

Feeding on the edge: foraging White Ibis target inter‐habitat prey fluxes

Avian population dynamics are influenced by the availability of spatiotemporally variable prey resources, but the conditions producing abundant and accessible prey are not always clear. In the Florida Everglades, wading birds nest in the dry season when receding water levels concentrate prey and facilitate improved foraging efficiency. White Ibis (Eudocimus albus) feed extensively on crayfish in sloughs, and previous studies have demonstrated that crayfish move downgradient from higher elevation, heavily vegetated ridge habitats into adjacent less‐vegetated sloughs when ridges are almost dry. Most White Ibis foraging is thought to occur in sloughs with relatively shallow water (< 19 cm), but crayfish move and their densities peak when water in sloughs is deeper (~ 21–32 cm). We conducted an observational study of White Ibis foraging in drying wetlands to determine if White Ibis restricted their foraging to shallow water or if they foraged in relatively deep water when crayfish were migrating. In a series of large drying wetlands, we used time‐lapse imagery to quantify White Ibis foraging activity over 61 d from February to April 2017 and we also quantified crayfish biomass density in sloughs. Crayfish biomass density peaked when ridges were almost dry. Most White Ibis foraging occurred over 2–3 d when ridges were almost dry and water in sloughs averaged ≥ 29 cm deep. White Ibis selected slough edges for foraging, suggesting that they were capturing crayfish migrating between habitats. Our results point to a new mechanism of prey exploitation driven by inter‐habitat prey flux when ridge habitat dries. Although the results of previous studies suggest that White Ibis will not forage on fish in deeper water (> 25 cm), we found that White Ibis will forage on crayfish in water at those depths. Maintenance of habitat elevational differences and hydro‐patterns that promote crayfish production will be necessary to promote this predator–prey interaction in the ridge‐slough landscape of the Everglades.     

Species-Habitat Relationships and Priority Areas for Marsh-Breeding Birds in Ontario

Populations of marsh-breeding birds have declined throughout the southern Laurentian Great Lakes basin. To advance conservation of these species, we used occupancy modeling, a regional prioritization scheme, and data from Birds Canada's Great Lakes Marsh Monitoring Program (2016–2018) to describe species-habitat relationships and identify priority habitat areas for 7 obligate marsh-breeding bird species in southern Ontario, Canada: American bittern (Botaurus lentiginosus), common gallinule (Gallinula galeata), least bittern (Ixobrychus exilis), marsh wren (Cistothorus palustris), pied-billed grebe (Podilymbus podiceps), sora (Porzana carolina), and Virginia rail (Rallus limicola). Given these species respond to land cover at widely varying spatial scales, we initially identified the most informative scale (buffer = 100 m, 200 m, 400 m, 800 m, 1,600 m, 3,200 m, or 6,400 m) for marsh, urban, agricultural, and forest cover to increase model performance. We also considered climate variables, whether sample sites were along a Great Lakes coastline or inland, and covariates influencing detection. Occupancy was best explained by land cover at a wide range of spatial scales depending on the species. All species except Virginia rail responded positively to marsh cover; American bittern and Virginia rail responded negatively to urban cover; least bittern, pied-billed grebe, and Virginia rail responded negatively and sora responded positively to agricultural cover; and American bittern, common gallinule, marsh wren, and pied-billed grebe responded negatively and Virginia rail responded positively to forest cover. Only American bittern responded negatively to mean May–June temperature; only pied-billed grebe responded positively to start of growing season; and only Virginia rail had higher occupancy at inland marshes compared to coastal. We combined predictions from the best model for each of 5 species with reasonably good model fit (we excluded sora and Virginia rail) to identify priority habitat areas for marsh-breeding birds. Expansion of wetland conservation work from existing priority areas based on waterfowl to also include these new additional priority areas based on marsh-breeding birds will be an important step towards conservation of all birds, and will help slow or maybe even reverse declining population trends. Some restoration activities outside but adjacent to priority areas will also be important for rebuilding marshes for these species across this intensively farmed and developed region. © 2020 The Wildlife Society.