350 research outputs found
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Seed and establishment limitation contribute to long-term native forb declines in California grasslands
The effects of exotic species invasions on biodiversity vary with spatial scale, and documentation of local-scale changes in biodiversity following invasion is generally lacking. Coupling long-term observations of local community dynamics with experiments to determine the role played by exotic species in recruitment limitation of native species would inform both our understanding of exotic impacts on natives at local scales and regional-scale management efforts to promote native persistence. We used field experimentation to quantify propagule and establishment limitation in a suite of native annual forbs in a California reserve, and compared these findings to species abundance trends within the same sites over the past 48 years. Observations at 11 paired sites (inside and outside the reserve) indicated that exotic annual plants have continued to increase in abundance over the past 48 years. This trend suggests the system has not reached equilibrium >250 years after exotic species began to spread, and 70 years after livestock grazing ceased within the reserve. Long-term monitoring observations also indicated that six native annual forb species went extinct from more local populations than were colonized. To determine the potential role of exotic species in these native plant declines, we added seed of these species into plots adjacent to monitoring sites where plant litter and live grass competition were removed. Experimental results suggest both propagule and establishment limitation have contributed to local declines observed for these native forbs. Recruitment was highest at sites that had current or historical occurrences of the seeded species, and in plots where litter was removed. Grazing history (i.e., location within or outside the reserve) interacted with exotic competition removal, such that removal of live grass competition increased recruitment in more recently grazed sites. Abundance of forbs was positively related to recruitment, while abundance of exotic forbs was negatively related. Thus, exotic competition is likely only one factor contributing to local declines of native species in invaded ecosystems, with a combination of propagule limitation, site quality, and land use history also playing important and interactive roles in native plant recruitment.This is the publisher’s final pdf. The published article is copyrighted by Ecological Society of America and can be found at: http://www.esa.org/.Keywords: Recruitment limitation, Community assembly, Livestock grazing, USA grasslands, Exotic species, California, Competition, Invasion, Propagule limitationKeywords: Recruitment limitation, Community assembly, Livestock grazing, USA grasslands, Exotic species, California, Competition, Invasion, Propagule limitatio
Viral diversity and prevalence gradients in North American Pacific Coast grasslands
Host-pathogen interactions may be governed by the number of pathogens coexisting within an individual host (i.e., coinfection) and among different hosts, although most sampling in natural systems focuses on the prevalence of single pathogens and/or single hosts. We measured the prevalence of four barley and cereal yellow dwarf viruses (B/CYDVs) in three grass species at 26 natural grasslands along a 2000-km latitudinal gradient in the western United States and Canada. B/CYDVs are aphid-vectored RNA viruses that cause one of the most prevalent of all plant diseases worldwide. Pathogen prevalence and coinfection were uncorrelated, suggesting that different forces likely drive them. Coinfection, the number of viruses in a single infected host (alpha diversity), did not differ among host species but increased roughly twofold across our latitudinal transect. This increase in coinfection corresponded with a decline in among-host pathogen turnover (beta diversity), suggesting that B/CYDVs in northern populations experience less transmission limitation than in southern populations. In contrast to pathogen diversity, pathogen prevalence was a function of host identity as well as biotic and abiotic environmental conditions. Prevalence declined with precipitation and increased with soil nitrate concentration, an important limiting nutrient for hosts and vectors of B/CYDVs. This work demonstrates the need for further studies of processes governing coinfection, and the utility of applying theory developed to explain diversity in communities of free-living organisms to pathogen systems
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Coastal protection and conservation on sandy beaches and dunes : Context-dependent tradeoffs in ecosystem service supply
Managing multiple ecosystem services (ESs) across landscapes presents a central challenge for ecosystem-based management, because services often exhibit spatiotemporal variation and weak associations with co-occurring ESs. Further focus on the mechanistic relationships among ESs and their underlying biophysical processes provides greater insight into the causes of variation and covariation among ESs, thus serving as a guide to enhance their supply while preventing adverse outcomes. Here, we used the U.S. Pacific Northwest coastal dune ecosystem to examine how invasive beachgrass management affects three ESs: coastal protection, western snowy plover conservation, and endemic foredune plant conservation. At seven coastal dune habitat restoration areas, we observed spatial variation in the supply of each ES and further identified a tradeoff between western snowy plover conservation and coastal protection. While the ESs were collectively influenced by the invasive beachgrasses and the foredunes they create, the magnitude of the synergies and tradeoffs were influenced by numerous non-shared drivers, including nearshore geomorphology, changes in foredune shape as a result of restoration, and other management actions irrespective of restoration. Incorporation of these shared and non-shared drivers into future coastal management planning may reduce tradeoffs among Pacific Northwest dune ESs. With better understanding of ES relationships, it becomes possible to identify management actions that may enhance synergies and mitigate tradeoffs, leading to better decisions for nature and people. Key words: coastal protection; conservation; ecosystem management; ecosystem services; natural capital; restoration
The synergistic response of primary production in grasslands to combined nitrogen and phosphorus addition is caused by increased nutrient uptake and retention
Background and aims A synergistic response of aboveground plant biomass production to combined nitrogen (N) and phosphorus (P) addition has been observed in many ecosystems, but the underlying mechanisms and their relative importance are not well known. We aimed at evaluating several mechanisms that could potentially cause the synergistic growth response, such as changes in plant biomass allocation, increased N and P uptake by plants, and enhanced ecosystem nutrient retention.
Methods We studied five grasslands located in Europe and the USA that are subjected to an element addition experiment composed of four treatments: control (no element addition), N addition, P addition, combined NP addition.
Results Combined NP addition increased the total plant N stocks by 1.47 times compared to the N treatment, while total plant P stocks were 1.62 times higher in NP than in single P addition. Further, higher N uptake by plants in response to combined NP addition was associated with reduced N losses from the soil (evaluated based on soil δ15N) compared to N addition alone, indicating a higher ecosystem N retention. In contrast, the synergistic growth response was not associated with significant changes in plant resource allocation.
Conclusions Our results demonstrate that the commonly observed synergistic effect of NP addition on aboveground biomass production in grasslands is caused by enhanced N uptake compared to single N addition, and increased P uptake compared to single P addition, which is associated with a higher N and P retention in the ecosystem
The synergistic response of primary production in grasslands to combined nitrogen and phosphorus addition is caused by increased nutrient uptake and retention
Background and aimsA synergistic response of aboveground plant biomass production to combined nitrogen (N) and phosphorus (P) addition has been observed in many ecosystems, but the underlying mechanisms and their relative importance are not well known. We aimed at evaluating several mechanisms that could potentially cause the synergistic growth response, such as changes in plant biomass allocation, increased N and P uptake by plants, and enhanced ecosystem nutrient retention.MethodsWe studied five grasslands located in Europe and the USA that are subjected to an element addition experiment composed of four treatments: control (no element addition), N addition, P addition, combined NP addition.ResultsCombined NP addition increased the total plant N stocks by 1.47 times compared to the N treatment, while total plant P stocks were 1.62 times higher in NP than in single P addition. Further, higher N uptake by plants in response to combined NP addition was associated with reduced N losses from the soil (evaluated based on soil delta N-15) compared to N addition alone, indicating a higher ecosystem N retention. In contrast, the synergistic growth response was not associated with significant changes in plant resource allocation.ConclusionsOur results demonstrate that the commonly observed synergistic effect of NP addition on aboveground biomass production in grasslands is caused by enhanced N uptake compared to single N addition, and increased P uptake compared to single P addition, which is associated with a higher N and P retention in the ecosystem
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Non-random biodiversity loss underlies predictable increases in viral disease prevalence
Disease dilution (reduced disease prevalence with increasing biodiversity) has been described for
many different pathogens. Although the mechanisms causing this phenomenon remain unclear,
the disassembly of communities to predictable subsets of species, which can be caused by
changing climate, land use, or invasive species, underlie one important hypothesis. In this case,
infection prevalence will reflect the competence of the remaining hosts. To test this hypothesis,
we measured local host species abundance and prevalence of four generalist aphid-vectored
pathogens (barley and cereal yellow dwarf viruses) in a ubiquitous annual grass host at ten sites
spanning 2000 kilometers along the North American West Coast. In lab and field trials, we
measured viral infection, and aphid fecundity and feeding preference on several host species.
Virus prevalence increased as local host richness declined. Community disassembly was non
random: ubiquitous hosts dominating species-poor assemblages were among the most competent
for vector production and virus transmission. This suggests that non-random biodiversity loss led
to increased virus prevalence. Because diversity loss is occurring globally in response to
anthropogenic changes, such work can inform medical, agricultural, and veterinary disease
research by providing insights into the dynamics of pathogens nested within a complex web of
environmental forces.This is an author's peer-reviewed final manuscript, as accepted by the publisher. The article is copyrighted by the author(s) and published by The Royal Society. It can be found at: http://rsif.royalsocietypublishing.org/.KEYWORDS: Vector-borne pathogen, Bromus hordeaceus, Rhopalosiphum padi (Aphididae), Disease dilution, Nestedness, Barley and cereal yellow dwarf viruses (B/CYDVs, Luteoviridae
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Invasive Congeners Differ in Successional Impacts across Space and Time
Invasive species can alter the succession of ecological communities because they are
often adapted to the disturbed conditions that initiate succession. The extent to which this
occurs may depend on how widely they are distributed across environmental gradients and
how long they persist over the course of succession. We focus on plant communities of the
USA Pacific Northwest coastal dunes, where disturbance is characterized by changes in
sediment supply, and the plant community is dominated by two introduced grasses – the
long-established Ammophila arenaria and the currently invading A. breviligulata. Previous
studies showed that A. breviligulata has replaced A. arenaria and reduced community diversity.
We hypothesize that this is largely due to A. breviligulata occupying a wider distribution
across spatial environmental gradients and persisting in later-successional habitat than A.
arenaria. We used multi-decadal chronosequences and a resurvey study spanning 2 decades
to characterize distributions of both species across space and time, and investigated
how these distributions were associated with changes in the plant community. The invading
A. breviligulata persisted longer and occupied a wider spatial distribution across the dune,
and this corresponded with a reduction in plant species richness and native cover. Furthermore,
backdunes previously dominated by A. arenaria switched to being dominated by A.
breviligulata, forest, or developed land over a 23-yr period. Ammophila breviligulata likely invades
by displacing A. arenaria, and reduces plant diversity by maintaining its dominance
into later successional backdunes. Our results suggest distinct roles in succession, with A.
arenaria playing a more classically facilitative role and A. breviligulata a more inhibitory role.
Differential abilities of closely-related invasive species to persist through time and occupy
heterogeneous environments allows for distinct impacts on communities
during succession
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