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Aechmea bracteata is a common epiphytic bromeliad found in symbiosis with many other species throughout tropical forests of Mexico and south through Panama. Given its importance and distribution in these forests, we asked how may ...
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Aechmea bracteata is a common epiphytic bromeliad found in symbiosis with many other species throughout tropical forests of Mexico and south through Panama. Given its importance and distribution in these forests, we asked how may A. bracteata be restored to areas where they have thrived in the past? We first investigated seed viability and response of seed germination to temperature, humidity, vapour pressure deficit (VPD), and light, under controlled growth chamber conditions. We recorded these environmental conditions within a seasonal tropical forest where this species is common and then conducted seed germination trials in various seral stages. In growth chambers, with constant water supply, highest germination percentages were at the highest temperature and lowest VPD levels. In the field, germination was less than 1%. Because of high temperatures and VPD within early seral stages, efforts to re-introduce A. bracteata into forests <20 years old are not likely to be successful.
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摘要 :
Aechmea bracteata is a common epiphytic bromeliad found in symbiosis with many other species throughout tropical forests of Mexico and south through Panama. Given its importance and distribution in these forests, we asked how may ...
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Aechmea bracteata is a common epiphytic bromeliad found in symbiosis with many other species throughout tropical forests of Mexico and south through Panama. Given its importance and distribution in these forests, we asked how may A. bracteata be restored to areas where they have thrived in the past? We first investigated seed viability and response of seed germination to temperature, humidity, vapour pressure deficit (VPD), and light, under controlled growth chamber conditions. We recorded these environmental conditions within a seasonal tropical forest where this species is common and then conducted seed germination trials in various seral stages. In growth chambers, with constant water supply, highest germination percentages were at the highest temperature and lowest VPD levels. In the field, germination was less than 1%. Because of high temperatures and VPD within early seral stages, efforts to re-introduce A. bracteata into forests <20 years old are not likely to be successful.
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1. Nest predation limits avian fitness, so birds should favour nest sites that minimize predation risk. Nevertheless, preferred nest microhabitat features are often uncorrelated with apparent variation in predation rates. 2. This ...
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1. Nest predation limits avian fitness, so birds should favour nest sites that minimize predation risk. Nevertheless, preferred nest microhabitat features are often uncorrelated with apparent variation in predation rates. 2. This lack of congruence between theory-based expectation and empirical data may arise when birds already occupy 'adaptive peaks'. If birds nest exclusively in low-predation microhabitats, microhabitat and nest predation may no longer be correlated even though predation ultimately shaped microhabitat selection. 3. This 'adaptive peak hypothesis' was tested for a population of Yellow Warblers (Dendroica petechia) focusing on two nest microhabitat features: concealment and height. Experimental nests measured relative predation risk both within and outside the microhabitat range typically occupied by natural nests to examine whether nest site choices made by birds restricted our ability to detect microhabitat effects on predation. 4. Within the natural range (30-80% concealment, > 75 cm height), microhabitat-predation relationships were weak and inconsistent, and similar for experimental and natural nests. Over an extended range, however, experimental predation rates were elevated in exposed sites (<30% concealed), indicating a concealment-related 'adaptive plateau'. 5. Clay egg bite data revealed a concealment effect on avian predators, and the abundance of one avian predator group correlated with nest concealment among years, suggesting these predators may cue birds to modulate nest concealment choices. 6. This study demonstrates how avian responses to predation pressure can obscure the adaptive significance of nest site selection, so predation influences may be more important than apparent from published data.
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Concern over rapid global changes and the potential for interactions among multiple threats are prompting scientists to combine multiple modelling approaches to understand impacts on biodiversity. A relatively recent development i...
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Concern over rapid global changes and the potential for interactions among multiple threats are prompting scientists to combine multiple modelling approaches to understand impacts on biodiversity. A relatively recent development is the combination of species distribution models, land-use change predictions, and dynamic population models to predict the relative and combined impacts of climate change, land-use change, and altered disturbance regimes on species' extinction risk. Each modelling component introduces its own source of uncertainty through different parameters and assumptions, which, when combined, can result in compounded uncertainty that can have major implications for management. Although some uncertainty analyses have been conducted separately on various model components - such as climate predictions, species distribution models, land-use change predictions, and population models - a unified sensitivity analysis comparing various sources of uncertainty in combined modelling approaches is needed to identify the most influential and problematic assumptions. We estimated the sensitivities of long-run population predictions to different ecological assumptions and parameter settings for a rare and endangered annual plant species (Acanthomintha ilicifolia, or San Diego thornmint). Uncertainty about habitat suitability predictions, due to the choice of species distribution model, contributed most to variation in predictions about long-run populations.Digital Object Identifier http://dx.doi.org/10.1111/gcb.12090
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Understanding and predicting the responses of plant communities to multiple overlapping disturbances remains a challenging task. Hurricane Wilma represents a large, yet infrequent type of disturbance that was superimposed on an ex...
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Understanding and predicting the responses of plant communities to multiple overlapping disturbances remains a challenging task. Hurricane Wilma represents a large, yet infrequent type of disturbance that was superimposed on an existing disturbance gradient of time since fire. We examined disturbance and recovery patterns in response to these overlapping disturbances by measuring how canopy structure, fine roots, mycorrhizae, and soil nitrogen dynamics, varied along a fire chronosequence in the 2 years after Hurricane Wilma. Hurricane damage increased canopy openness in all seral stages. In the early-seral stage, canopy openness returned to pre-hurricane conditions within 2 years, whereas canopy openness in the late-seral stage remained significantly higher throughout the study. We observed no significant change in root length density in the early- and mid-seral stages. However, in the late-seral stage, root length density was significantly reduced immediately after the hurricane and remained so 2 years after the hurricane. In the late-seral stage, we also observed a significant reduction in percent soil nitrogen and a significant increase in soil nitrogen isotopic composition (tp#eN) values, indicating a loss of soil nitrogen. In contrast, in the early- and mid-seral stages, there were no significant changes in percent nitrogen or soil tp#eN values. Results from this study suggest that forest fire disturbance history influences responses to hurricane damage. Moreover, feedbacks between aboveground and belowground processes have the potential to influence forest recovery.
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Multiple processes are increasingly recognized as being responsible for species' extinctions. We evaluated population extinctions between 1930 and 1998 for the endangered Quino checkerspot (Euphydryas editha quino) butterfly relat...
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Multiple processes are increasingly recognized as being responsible for species' extinctions. We evaluated population extinctions between 1930 and 1998 for the endangered Quino checkerspot (Euphydryas editha quino) butterfly relative to agricultural history, human population growth, climate variability, topographical diversity, and wildflower abundance. Overall agricultural land use was calculated for extinct and extant populations based upon cultivation and grazing intensities averaged across five time periods reflecting distinct agricultural practices from 1769 to present. Extinct populations were associated with a history of more intensive agriculture and greater human population growth at time of extinction. A long history of intensive livestock grazing was the strongest agricultural predictor of extinction. Based upon historic vegetation maps, extinct butterfly populations were typically isolated from other known populations by 1930, and in landscapes fragmented by cultivation and development. Precipitation and topographical variability were not important predictors of extinction. Wildflower host plants and nectar sources have declined across the butterfly's range because of invasive plants and habitat loss. The proportion of years considered average or abundant in wildflowers declined significantly during extinction periods. The Quino checkerspot has shifted in distribution from the coast into foothills and mountains. Newly discovered higher elevation populations experience more precipitation and are buffered from drought. Efforts to conserve Quino checkerspot are enhanced by understanding that the butterfly's decline and shifting distribution is a complex multi-scale process related to agricultural history, human population growth, climate variability, and wildflower decline.
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The shift from single species conservation initiatives to multiple-species conservation plans has not been accompanied by parallel changes in methods to evaluate the success of these efforts, nor to provide managers critical infor...
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The shift from single species conservation initiatives to multiple-species conservation plans has not been accompanied by parallel changes in methods to evaluate the success of these efforts, nor to provide managers critical information to employ adaptive management strategies. Layering single species approaches for monitoring multiple-species conservation plans is inefficient and may lead to management strategies that have unintended detrimental impacts on target and nontarget organisms. Alternative approaches, such as ecosystem monitoring, can also fail to provide adequate protection for listed species and so may not fulfill regulatory requirements. We propose a hybrid approach that employs conceptual and spatial data in an iterative process to create niche models for species and species associations within natural communities. Niche models are composed of testable hypotheses linking species occurrences to environmental parameters over multiple scales. During an initial data gathering period these hypotheses are evaluated, accepted or rejected, and modified as indicated by new data. Once niche models are corroborated, the focus of monitoring shifts to a greater emphasis on identified anthropogenic and natural environmental drivers of species occurrence and abundance. The focus on environmental drivers supplies managers with direct information as to how, when, and where to employ adaptive management strategies when natural variance in those drivers is compromised by anthropogenic stressors. We provide a specific example on the conceptualization, development, and implementation of our hybrid approach from a new Multiple-species Habitat Conservation Plan for the Coachella Valley, in the Colorado desert of southern California.
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The current distribution (2009) and survey methodologies are provided for detecting the Coachella Valley Jerusalem Cricket (Stenopelmatus cahuilaensis Tinkham 1968). When several survey methodologies are assessed, we found that, i...
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The current distribution (2009) and survey methodologies are provided for detecting the Coachella Valley Jerusalem Cricket (Stenopelmatus cahuilaensis Tinkham 1968). When several survey methodologies are assessed, we found that, in the absence of debris, the use of cover-boards and the examination of areas beneath cow manure pats (cow chips) to be the most efficient and least destructive ways of detecting this rare and unique desert species. When using these methods we were able to establish the current distribution of the insect and compare it to historical records. The present distribution of the cricket suggests that it is currently undergoing a westward movement in its range as well as an overall range contraction possibly as a result of climate change.Digital Object Identifier http://dx.doi.org/10.3956/2010-17.1
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Sahara Mustard (Brassica tournefortii; hereafter mustard), an exotic plant species, has invaded habitats throughout the arid southwestern United States. Mustard has reached high densities across aeolian sand habitats of southweste...
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Sahara Mustard (Brassica tournefortii; hereafter mustard), an exotic plant species, has invaded habitats throughout the arid southwestern United States. Mustard has reached high densities across aeolian sand habitats of southwestern deserts, including five distinct sand habitats in the eastern Coachella Valley, California. We examined trends in ground-dwelling arthropod community structure concurrent with mustard invasion in 90 plots within those habitats from 2003 to 2011 (n = 773 plot-years). We expected arthropod communities to respond negatively to mustard invasion because previous work documented significant negative impacts of mustard on diversity and biomass of native plants, the primary resource base for many of the arthropods. Arthropod abundance and species richness declined during the study period while mustard cover increased, and arthropod metrics were negatively related to mustard cover across all plots. When controlling for non-target environmental correlates (e.g. perennial frequency and precipitation) and for potential factors that we suspected of mediating mustard effects (e.g. native cover and sand compaction), negative relationships with mustard remained statistically supported. Nevertheless, arthropod richness's relationship decreased slightly in strength and significance suggesting that mechanistic pathways may be both direct (via habitat structure) and indirect (via native cover suppression and sand compaction). However, mechanistic pathways for mustard effects, particularly on arthropod abundance, remain unclear. Most arthropod taxa, including most detritivores, decreased through time and were negatively related to mustard cover. In contrast, many predators were positively related to mustard. In total, our study provides substantial evidence for a negative effect of Sahara mustard on the structure of a ground-dwelling arthropod community.
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The sources of water used by woody vegetation growing on karst soils in seasonally dry tropical regions are little known. In northern Yucatan (Mexico), trees withstand 4–6 months of annual drought in spite of the small water stor...
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The sources of water used by woody vegetation growing on karst soils in seasonally dry tropical regions are little known. In northern Yucatan (Mexico), trees withstand 4–6 months of annual drought in spite of the small water storage capacity of the shallow karst soil. We hypothesized that adult evergreen trees in Yucatan tap the aquifer for a reliable supply of water during the prolonged dry season. The naturally occurring concentration gradients in oxygen and hydrogen stable isotopes in soil, bedrock, groundwater and plant stem water were used to determine the sources of water used by native evergreen and drought-deciduous tree species. While the trees studied grew over a permanent water table (9–20 m depth), pit excavation showed that roots were largely restricted to the upper 2 m of the soil/bedrock profile. At the peak of the dry season, the δ18O signatures of potential water sources for the vegetation ranged from 4.1 ± 1.1‰ in topsoil to ?4.3 ± 0.1‰ in groundwater. The δ18O values of tree stem water ranged from ?2.8 ± 0.3‰ in Talisia olivaeformis to 0.8 ± 1‰ in Ficus cotinifolia, demonstrating vertical partitioning of soil/bedrock water among tree species. Stem water δ18O values were significantly different from that of groundwater for all the tree species investigated. Stem water samples plotted to the right of the meteoric water line, indicating utilization of water sources subject to evaporative isotopic enrichment. Foliar δ13C in adult trees varied widely among species, ranging from ?25.3 ± 0.3‰ in Enterolobium cyclocarpum to ?28.7 ± 0.4‰ in T. olivaeformis. Contrary to initial expectations, data indicate that native trees growing on shallow karst soils in northern Yucatan use little or no groundwater and depend mostly on water stored within the upper 2–3 m of the soil/bedrock profile. Water storage in subsurface soil-filled cavities and in the porous limestone bedrock is apparently sufficient to sustain adult evergreen trees throughout the pronounced dry season.
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