Trophic rewilding: impact on ecosystems under global change Bakker, Elisabeth S.; Svenning, Jens-Christian
Philosophical transactions of the Royal Society of London. Series B. Biological sciences,
10/2018, Letnik:
373, Številka:
1761
Journal Article
Aquatic plants fulfil a wide range of ecological roles, and make a substantial contribution to the structure, function and service provision of aquatic ecosystems. Given their well-documented ...importance in aquatic ecosystems, research into aquatic plants continues to blossom. The 14th International Symposium on Aquatic Plants, held in Edinburgh in September 2015, brought together 120 delegates from 28 countries and six continents. This special issue of Hydrobiologia includes a select number of papers on aspects of aquatic plants, covering a wide range of species, systems and issues. In this paper, we present an overview of current trends and future directions in aquatic plant research in the early twenty first century. Our understanding of aquatic plant biology, the range of scientific issues being addressed and the range of techniques available to researchers have all arguably never been greater; however, substantial challenges exist to the conservation and management of both aquatic plants and the ecosystems in which they are found. The range of countries and continents represented by conference delegates and authors of papers in the special issue illustrates the global relevance of aquatic plant research in the early twenty first century but also the many challenges that this burgeoning scientific discipline must address.
Global nutrient transport in a world of giants Doughty, Christopher E.; Roman, Joe; Faurby, Søren ...
Proceedings of the National Academy of Sciences - PNAS,
01/2016, Letnik:
113, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The past was a world of giants, with abundant whales in the sea and large animals roaming the land. However, that world came to an end following massive late-Quaternarymegafauna extinctions on land ...and widespread population reductions in great whale populations over the past few centuries. These losses are likely to have had important consequences for broad-scale nutrient cycling, because recent literature suggests that large animals disproportionately drive nutrient movement. We estimate that the capacity of animals to move nutrients away from concentration patches has decreased to about 8% of the preextinction value on land and about 5%of historic values in oceans. For phosphorus (P), a key nutrient, upward movement in the ocean by marine mammals is about 23% of its former capacity (previously about 340 million kg of P per year). Movements by seabirds and anadromous fish provide important transfer of nutrients from the sea to land, totalling ∼150 million kg of P per year globally in the past, a transfer that has declined to less than 4% of this value as a result of the decimation of seabird colonies and anadromous fish populations. We propose that in the past, marine mammals, seabirds, anadromous fish, and terrestrial animals likely formed an interlinked system recycling nutrients from the ocean depths to the continental interiors, with marine mammals moving nutrients from the deep sea to surface waters, seabirds and anadromous fish moving nutrients from the ocean to land, and large animals moving nutrients away from hotspots into the continental interior.
Climate change can promote harmful cyanobacteria blooms in eutrophic waters through increased droughts or flooding. In this paper, we explore how water-level fluctuations affect the occurrence of ...cyanobacterial blooms, and based on the observations from case studies, we discuss the options and pitfalls to use water-level fluctuations for lake and reservoir management. A drawdown in summer causes an increase in retention time and increased water column nutrient concentrations and temperature of shallow water layers, which may lead to severe cyanobacterial blooms. This effect can potentially be counteracted by the positive response of submerged macrophytes, which compete for nutrients with cyanobacteria, with a higher chance of cyanobacterial blooms under eutrophic conditions. The balance between dominance by submerged macrophytes or cyanobacteria is temperature sensitive with stronger positive effects of drawdown as inhibition of cyanobacterial blooms expected in colder climates. Complete drying out reduces the amount of cyanobacteria in the water column after refilling, with lower water nutrient concentrations, lower fish biomass, lower abundance of cyanobacteria, higher transparency, and higher cover of submerged plants compared to lakes and reservoirs that did not dry out. Water-level rise as response to flooding has contrasting effects on the abundance of cyanobacteria depending on water quality. We conclude that water-level fluctuation management has potential to mitigate cyanobacterial blooms. However, the success will depend strongly on ecosystem properties, including morphometry, sediment type, water retention time, quality of inlet water, presence of submerged vegetation or propagules, abundance of fish, and climate.
Until recently in Earth history, very large herbivores (mammoths, ground sloths, diprotodons, and many others) occurred in most of the World’s terrestrial ecosystems, but the majority have gone ...extinct as part of the late-Quaternary extinctions. How has this large-scale removal of large herbivores affected landscape structure and ecosystem functioning? In this review, we combine paleo-data with information from modern exclosure experiments to assess the impact of large herbivores (and their disappearance) on woody species, landscape structure, and ecosystem functions. In modern landscapes characterized by intense herbivory, woody plants can persist by defending themselves or by association with defended species, can persist by growing in places that are physically inaccessible to herbivores, or can persist where high predator activity limits foraging by herbivores. At the landscape scale, different herbivore densities and assemblages may result in dynamic gradients in woody cover. The late-Quaternary extinctions were natural experiments in large-herbivore removal; the paleoecological record shows evidence of widespread changes in community composition and ecosystem structure and function, consistent with modern exclosure experiments. We propose a conceptual framework that describes the impact of large herbivores on woody plant abundance mediated by herbivore diversity and density, predicting that herbivore suppression of woody plants is strongest where herbivore diversity is high. We conclude that the decline of large herbivores induces major alterations in landscape structure and ecosystem functions.
Abstract
Large mammalian herbivores are vital components of terrestrial ecosystems, influencing the plants they feed on, but also serving as ecosystem engineers that impact the occurrence and ...survival of many other organisms. Arthropods are the most abundant and diverse animal group on earth, filling all trophic levels in food webs and facilitating essential ecosystem services. However, the impacts of large herbivores on arthropod communities and the mechanisms via which these impacts are mediated are not fully understood.
Here, we experimentally separated the mechanistic pathways whereby large herbivores affect arthropod food webs using a 24‐year manipulative multi‐site field experiment in the Netherlands. We analysed the abundance, biomass and community composition of arthropods in the plant canopy and on the soil surface, both in grazed sites or sites where large herbivores were excluded.
We found that the presence of large herbivores resulted in considerable differences in vegetation properties and microclimate which influenced the abundance and biomass of arthropods to varying trophic levels. Large herbivore grazing enhanced the overall abundance and biomass of arthropod herbivores, pollinators, omnivores and soil‐dwelling predators, but reduced that of detritivores, scavengers, parasitoids and canopy predators. Structural equation models revealed that different trophic groups are affected by grazing via different pathways. Specially, large herbivores facilitated herbivores via increasing plant quality and enhanced ground‐dwelling predators via increasing plant diversity. In contrast, plant‐dwelling predators were suppressed via decreased plant quantity, and parasitoids were mainly affected by changes in microclimate conditions.
Synthesis
. Our results show that large mammalian herbivores play a significant role in shaping grassland arthropod food webs, and that these impacts were independently mediated by multiple aspects of vegetation properties, that is, physical structure, plant diversity, standing crop biomass and leaf nutrient content. Arthropods of different trophic groups responded differently to the large herbivores, and these functional group‐specific responses in turn may have strong cascading effects on numerous ecosystem services.
中文摘要
大型草食动物是陆地生态系统的重要组分，可以对植物及其赖以生存的生物产生重要影响。节肢动物是地球上数量最多且多样性最高的生物类群之一，不仅占据了食物网所有主要的营养级，同时在维持生态系统功能和服务中发挥关键作用。然而，大型食草动物如何影响节肢动物食物网以及背后的调节机制尚不清楚。
我们在荷兰进行的一项为期24年的多样点围栏实验阐明了大型草食动物对节肢动物食物网的影响及多重调节机制，这些机制主要依赖大型草食动物对植物群落特征和微环境的改变。我们对放牧围栏内外不同片层(植物冠层和土壤表面)节肢动物的数量、生物量和群落组成进行了详尽的调查。
我们发现大型草食动物会显著影响植物群落特征和微环境条件，从而对节肢动物不同营养级的数量和生物量产生不一致的影响:大型草食动物显著增加了植食者、传粉者、杂食者和生活在地表的捕食者的数量和生物量，但显著降低了分解者、食腐者、寄生者以及位于植物冠层的捕食者的数量和生物量。结构方程模型进一步揭示了大型动物对不同营养级节肢动物的作用途径:大型草食动物可以通过提高植物质量促进植食者，通过增加植物多样性促进地表捕食者。相反，大型草食动物通过减少植物数量降低植物冠层的捕食者，通过改变微气候条件对寄生者产生影响。
我们的研究表明大型草食动物在塑造节肢动物食物网中发挥着重要作用，并且这些作用受植物群落特征的不同方面(植物多样性，植物数量，植物质量，植物群落结构等)调节。同时，节肢动物不同营养级对大型草食动物的响应差异，可能会对生态系统的结构和功能产生潜在影响。
Tropical rainforests are populated by large frugivores that feed upon fruit‐producing woody species, yet their role in regulating the cycle of globally important biogeochemical elements such as ...nitrogen is still unknown. This is particularly relevant because tropical forests play a prominent role in the nitrogen cycle and are becoming rapidly defaunated. Furthermore, frugivory is not considered in current plant‐large herbivore‐nutrient cycling frameworks exclusively focused on grazers and browsers.
Here we used a long‐term replicated paired control‐exclusion experiment in the Atlantic Forest of Brazil, where peccaries and tapirs are the largest native frugivores, to examine the impact of large ground‐dwelling frugivores on modulating soil nitrogen cycling, considering their effects across a gradient of abundance of a hyper‐dominant palm.
We found that both large frugivores and dominant palms play a substantial role in modulating ammonium availability and nitrification rates. Large frugivores increased ammonium by 95%, which also increased additively with palm abundance. Nitrification rates increased with palm abundance in the presence of large frugivores, but not on exclosure plots. Large frugivores also stimulated the regulation of the functions of soil‐nitrifying microorganisms, and modulated the landscape‐scale variance in nitrogen availability. Such joint effects of large frugivores and palms are consistent with the notion of ‘fruiting lawns’.
Our study indicates that frugivory plays a pivotal role in zoogeochemistry in tropical forests by regulating and structuring the nitrogen cycle, urging to accommodate frugivory in plant‐large herbivore‐nutrient cycling frameworks. It also indicates that defaunation, deforestation and illegal palm and timber harvesting seriously affect nitrogen cycling in tropical forests, that play a prominent role in the global cycle of this nutrient.
A free Plain Language Summary can be found within the Supporting Information of this article.
Resumo
As florestas tropicais são habitadas por grandes mamíferos que se alimentam de frutos de espécies lenhosas, no entanto, o papel ecológico desses animais na ciclagem de elementos biogeoquímicos globalmente importantes como o nitrogênio é ainda desconhecido. Este tema é particularmente relevante porque florestas tropicais desempenham uma função fundamental no ciclo do nitrogênio e estão sendo defaunadas rapidamente. Além disso, a frugivoria não é atualmente considerada nos modelos teóricos que envolvem plantas, grandes herbívoros e ciclagem de nutrientes, os quais tem sido unicamente focados em herbívoros pastadores e podadores.
Nesse estudo, nós utilizamos um experimento replicado de longo prazo que contém pares de parcelas abertas e de exclusão de grandes mamíferos na Mata Atlântica brasileira onde queixadas e antas são os maiores frugívoros nativos. O objetivo foi avaliar o impacto desses grandes frugívoros terrestres na modulação da ciclagem de nitrogênio no solo considerando seus efeitos ao longo de um gradiente de abundância de uma palmeira hiper dominante.
Nós encontramos que tanto os frugívoros de grande porte como as palmeiras desempenham uma função substancial na modulação da disponibilidade de amônio no solo e das taxas de nitrificação. Os grandes frugívoros aumentaram a concentração de amônio em 95%, que também teve um incremento aditivo com a abundância de palmeiras. As taxas de nitrificação aumentaram com a abundância de palmeiras na presença de grandes frugívoros, mas não em parcelas de exclusão. Os grandes frugívoros também estimularam a regulação das funções dos microorganismos nitrificantes e modularam a variação da disponibilidade de nitrogênio à escala da paisagem. Tais efeitos em conjunto de grandes frugívoros e palmeiras são consistentes com a noção de “sítios de frutificação”.
Nosso estudo indica que a frugivoria tem uma função fundacional na zoogeoquímica das florestas tropicais pela regulação e estruturação do ciclo do nitrogênio. Torna‐se urgente incluir a frugivoria aos modelos ecológicos que envolvem plantas, grandes herbívoros e ciclagem de nutrientes. Esses resultados também indicam que a defaunação, o desmatamento e exploração ilegal de palmeiras e madeira afetam severamente a dinâmica do nitrogênio em florestas tropicais, as quais são partes cruciais na ciclagem global desse nutriente.
A free Plain Language Summary can be found within the Supporting Information of this article.
While large herbivores can have strong impacts on terrestrial ecosystems, much less is known of their role in aquatic systems. We reviewed the literature to determine: 1) which large herbivores (> 10 ...kg) have a (semi‐)aquatic lifestyle and are important consumers of submerged vascular plants, 2) their impact on submerged plant abundance and species composition, and 3) their ecosystem functions. We grouped herbivores according to diet, habitat selection and movement ecology: 1) Fully aquatic species, either resident or migratory (manatees, dugongs, turtles), 2) Semi‐aquatic species that live both in water and on land, either resident or migratory (swans), 3) Resident semi‐aquatic species that live in water and forage mainly on land (hippopotamuses, beavers, capybara), 4) Resident terrestrial species with relatively large home ranges that frequent aquatic habitats (cervids, water buffalo, lowland tapir). Fully aquatic species and swans have the strongest impact on submerged plant abundance and species composition. They may maintain grazing lawns. Because they sometimes target belowground parts, their activity can result in local collapse of plant beds. Semi‐aquatic species and turtles serve as important aquatic–terrestrial linkages, by transporting nutrients across ecosystem boundaries. Hippopotamuses and beavers are important geomorphological engineers, capable of altering the land and hydrology at landscape scales. Migratory species and terrestrial species with large home ranges are potentially important dispersal vectors of plant propagules and nutrients. Clearly, large aquatic herbivores have strong impacts on associated species and can be critical ecosystem engineers of aquatic systems, with the ability to modify direct and indirect functional pathways in ecosystems. While global populations of large aquatic herbivores are declining, some show remarkable local recoveries with dramatic consequences for the systems they inhabit. A better understanding of these functional roles will help set priorities for the effective management of large aquatic herbivores along with the plant habitats they rely on.
Land abandonment has been increasing in recent decades in Europe, usually accompanied by biodiversity decline. Whether livestock grazing and mowing can safeguard biodiversity across spatial scales in ...the long term is unclear.
Using a 48‐year experiment in a salt marsh, we compared land abandonment (without grazing and mowing) and seven management regimes including cattle grazing, early season mowing, late season mowing, both early and late season mowing, and grazing plus each of the mowing regimes on plant diversity at the local and larger scales (i.e. aggregated local communities). Also, we compared their effects on community composition (both in identities and abundances) in time and space.
Under land abandonment, plant diversity declined in the local communities and this decline became more apparent at the larger scale, particularly for graminoids and halophytes. All management regimes, except for late season mowing, maintained plant diversity at these scales.
Local plant communities under all treatments underwent different successional trajectories, in the end, diverged from their initial state except for that under grazing (a cyclic succession). Year‐to‐year changes in local community composition remained at a similar level over time under land abandonment and grazing plus early season mowing while it changed under other treatments. Vegetation homogenized at the larger scale over time under land abandonment while vegetation remained heterogeneous under all management regimes.
Synthesis. Our experiment suggests that late season mowing may not be sustainable to conserve plant diversity in salt marshes. Other management regimes can maintain plant diversity across spatial scales and vegetation heterogeneity at the larger scale in the long term, but local community composition may change over time.
A 48‐year experiment reveals that, compared with land abandonment, cattle grazing, early season mowing, both early and late season mowing (but not late season mowing), and grazing plus each of the mowing regimes maintained plant diversity across spatial scales.
Eutrophication and globalisation facilitate the dominance of exotic plants in aquatic ecosystems worldwide. Aquatic omnivores can provide biotic resistance to plant invasions, but little is known ...about whether obligate aquatic herbivores can do the same. Herbivores such as insects can decimate aquatic vegetation, but may not be able to consume exotic plants due to their more or less specialised nature of feeding. We experimentally tested the larval feeding of an aquatic insect, the moth
Parapoynx stratiotata
, on eleven submerged plant species, from either native or exotic origin. We also tested whether insect herbivory stimulates nutrient and organic matter release, thus affecting water quality. Larvae of
P. stratiotata
consumed seven out of eleven plant species, and their growth was related to plant nutrient content and stoichiometry. However, larvae had no preference for either native or exotic macrophytes, and their plant preference was not related to the measured plant traits, but was possibly driven by secondary metabolites. Through plant consumption, caterpillars induced brownification and phosphate release, and the intensity thereof varied among plant species, but not between native and exotic plants. In conclusion,
P. stratiotata
showed strong feeding preferences demonstrating that aquatic insects can directly and indirectly alter water quality and vegetation composition.
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