The effects of landscape history and time-lags on plant invasion in Mediterranean coastal habitats

Human-driven landscape changes may promote plant invasions by increasing propagule pressure and providing favourable conditions for non-native species to establish and spread. The increase in invasion levels might not be immediate but rather exhibit a time-lag (i.e. invasion debt). Moreover, the relationship between invasion and landscape history (i.e. changes in landscape composition) might be extremely complex as it might also include extinction debts of invasive species currently in regression. In order to understand the effect of landscape history on plant invasion, we studied the invasion level in coastal plant communities affected by intense human-driven landscape alteration in the last 50 years. We identified all non-native plant species within 809 grid cells (250 × 250 m) along ~500 km of the Spanish SW coast. We tested the association of (1) non-native richness conditional on the overall presence of non-natives (at least one species), and (2) the occurrence of the most frequent non-native species, with the percentage of human land-cover categories in 1956, 1991 and 2007 using a multimodel inference approach. We used these models to project future invasion patterns in the region. We found non-native richness to be more associated with land-cover variables in 1956 than in 2007, suggesting the existence of an invasion debt, but not for the overall presence of non-natives. For most frequent species, the effects of past landscape alteration depended on the introduction pathway and the region of origin. Species used in agriculture were more related to past cropland area, while most of the species used in gardening or forestry showed higher affinity for recently altered areas. These results highlight the relevance of the species’ introduction history and landscape history in assessing future long-term invasion trends.     

Contrasting patterns of intraspecific trait variability in native and non-native plant species along an elevational gradient on Tenerife,Canary Islands

Background and AimsNon-native plant species are not restricted to lowlands, but increasingly are invading high elevations. While for both native and non-native species we expected variability of plant functional traits due to the changing environmental conditions along elevational gradients, we additionally assumed that non-native species are characterized by a more acquisitive growth strategy, as traits reflecting such a strategy have been found to correlate with invasion success. Furthermore, the typical lowland introduction of non-native species coming from multiple origins should lead to higher trait variability within populations of non-native species specifically at low elevations, and they might therefore occupy a larger total trait space.MethodsAlong an elevational gradient ranging from 55 to 1925 m a.s.l. on Tenerife, we collected leaves from eight replicate individuals in eight evenly distributed populations of five native and six non-native forb species. In each population, we measured ten eco-morphological and leaf biochemical traits and calculated trait variability within each population and the total trait space occupied by native and non-native species.Key ResultsWe found both positive (e.g. leaf dry matter content) and negative (e.g. leaf N) correlations with elevation for native species, but only few responses for non-native species. For non-native species, within-population variability of leaf dry matter content and specific leaf area decreased with elevation, but increased for native species. The total trait space occupied by all non-native species was smaller than and a subset of that of native species.ConclusionsWe found little evidence that intraspecific trait variability is associated with the success of non-native species to spread towards higher elevations. Instead, for non-native species, our results indicate that intermediate trait values that meet the requirements of various conditions are favourable across the changing environmental conditions along elevational gradients. As a consequence, this might prevent non-native species from overcoming abruptly changing environmental conditions, such as when crossing the treeline.     

The role of environmental gradients in non-native plant invasion into burnt areas of Yosemite National Park, California

Fire is known to facilitate the invasion of many non-native plant species, but how invasion into burnt areas varies along environmental gradients is not well-understood. We used two pre-existing data sets to analyse patterns of invasion by non-native plant species into burnt areas along gradients of topography, soil and vegetation structure in Yosemite National Park, California, USA. A total of 46 non-native species (all herbaceous) were recorded in the two data sets. They occurred in all seven of the major plant formations in the park, but were least common in subalpine and upper montane conifer forests. There was no significant difference in species richness or cover of non-natives between burnt and unburnt areas for either data set, and environmental gradients had a stronger effect on patterns of non-native species distribution, abundance and species composition than burning. Cover and species richness of non-natives had significant positive correlations with slope (steepness) and herbaceous cover, while species richness had significant negative correlations with elevation, the number of years post-burn, and cover of woody vegetation. Non-native species comprised a relatively minor component of the vegetation in both burnt and unburnt areas in Yosemite (percentage species = 4%, mean cover < 6.0%), and those species that did occur in burnt areas tended not to persist over time. The results indicate that in many western montane ecosystems, fire alone will not necessarily result in increased rates of invasion into burnt areas. However, it would be premature to conclude that non-native species could not affect post-fire succession patterns in these systems. Short fire-return intervals and high fire severity coupled with increased propagule pressure from areas used heavily by humans could still lead to high rates of invasion, establishment and spread even in highly protected areas such as Yosemite.     

Positive effects of an extremely hot summer on propagule rain in upper alpine to subnival habitats of the Central Eastern Alps

Background: Propagule production and dispersal largely determine the distribution and potential migration ability of alpine plant species. Variation in reproductive success caused by year-to-year variation in climate may critically influence these processes.

Aims: To obtain estimates for the propagule rain in high-alpine plant communities and detect potential dispersal events from lower elevations.

Methods: The magnitude and composition of the propagule rain was studied in different plant communities along an elevation gradient from the upper alpine to subnival zone. Propagules were trapped at eight elevations from 2760 to 3070 m a.s.l. for three years from July to September 2003–2005. Vascular plant species and their cover were recorded in an area with a radius of 10 m surrounding the traps.

Results: A five- to 10-fold higher propagule rain was observed in 2003, a year with an exceptionally hot summer, compared to 2004 and 2005. Propagule and species numbers varied highly among years and community types. Few propagules of non-local origin were recorded in any year.

Conclusions: Extremely hot summers are likely to greatly magnify the propagule rain size of species in alpine habitats. Such ‘mast years’ may contribute to enhanced and accelerated vegetation changes in alpine habitats in the absence of limiting factors.     

Non-Native Plant Invasion along Elevation and Canopy Closure Gradients in a Middle Rocky Mountain Ecosystem

Mountain environments are currently among the ecosystems least invaded by non-native species; however, mountains are increasingly under threat of non-native plant invasion. The slow pace of exotic plant invasions in mountain ecosystems is likely due to a combination of low anthropogenic disturbances, low propagule supply, and extreme/steep environmental gradients. The importance of any one of these factors is debated and likely ecosystem dependent. We evaluated the importance of various correlates of plant invasions in the Wallowa Mountain Range of northeastern Oregon and explored whether non-native species distributions differed from native species along an elevation gradient. Vascular plant communities were sampled in summer 2012 along three mountain roads. Transects (n = 20) were evenly stratified by elevation (~70 m intervals) along each road. Vascular plant species abundances and environmental parameters were measured. We used indicator species analysis to identify habitat affinities for non-native species. Plots were ordinated in species space, joint plots and non-parametric multiplicative regression were used to relate species and community variation to environmental variables. Non-native species richness decreased continuously with increasing elevation. In contrast, native species richness displayed a unimodal distribution with maximum richness occurring at mid–elevations. Species composition was strongly related to elevation and canopy openness. Overlays of trait and environmental factors onto non-metric multidimensional ordinations identified the montane-subalpine community transition and over-story canopy closure exceeding 60% as potential barriers to non-native species establishment. Unlike native species, non-native species showed little evidence for high-elevation or closed-canopy specialization. These data suggest that non-native plants currently found in the Wallowa Mountains are dependent on open canopies and disturbance for establishment in low and mid elevations. Current management objectives including restoration to more open canopies in dry Rocky Mountain forests, may increase immigration pressure of non-native plants from lower elevations into the montane and subalpine zones.     

Flowering phenology and reproductive fitness along a mountain slope: maladaptive responses to transplantation to a warmer climate in Campanula thyrsoides

In many biomes, global warming has resulted in advanced and longer growing seasons, which has often led to earlier flowering in plant taxa. Elevational gradients are ideal to study the effects of global warming as they allow transplantation of plants from their original cooler higher elevations down to elevations with a prospective climate. We transplanted plants from ten populations of the European alpine monocarpic herb species Campanula thyrsoides L. to three sites along a steep mountain slope (600, 1,235 and 1,850 m above sea level) in the Swiss Alps and asked whether reproductive phenology adjusts plastically to elevation and if these responses were adaptive, i.e. increased the fitness of plants. We further assessed current genetic differentiation in phenotypic traits and whether any such origin effects were due to adaptation to climatic conditions of origin. Our results showed that transplantation to lower elevations caused strong shifts in phenology, with plants starting growth and flowering earlier than plants placed at higher elevations. However, compared to flower production at high elevation, number of flowers per plant decreased 21 % at mid- and 61 % at low elevation. The shift in phenology thus came with a high cost in fitness, and we suggest that phenology is maladaptive when C. thyrsoides faces temperature conditions deviating from its natural amplitude. We conclude that the frequently reported phenological shift in plant species as a response to global warming may include heavy fitness costs that may hamper species survival.     

River fish assemblages along an elevation gradient in the eastern extremity of Europe

Studies on assemblages of freshwater fishes along elevational gradients of rivers are lacking, even in Europe. In this paper we have explored the entire range of elevational gradients existing in the European part of Russia. We analyzed how fish biodiversity (species richness, abundance, diversity indices) at 435 river sites differed by elevation. The impact of elevation on the distribution of freshwater fish species was analyzed using regression and ordination methods. For the first time for a large area of Eastern Europe, optimum points and niche breadth for fish species along altitude gradients were estimated. Our analyses showed: (1) species richness and Shannon index decreased in the upper part of the gradient; fish abundance showed a unimodal response to elevation; highest numbers were found at elevations between 250 and 500 m; (2) ordination analysis demonstrated an upstream-downstream gradient of the fish assemblages; (3) regression analysis showed significant preferences for elevation by 19 species, all of which were monotonic; (4) optimum and niche breadth (tolerance) were highly variable between species; only five species (brown trout, grayling, common minnow, bullhead and stone loach) were encountered at elevations above 650 m; and (5) in our region, the habitat of grayling was higher in the mountains, and its abundance (numbers) at extreme elevations was greater, than brown trout. These results show how fish assemblages differ with elevation. Our findings identify the data that can be used for regional environmental monitoring of the state of small rivers and for aquatic conservation.     

Plant invasions in treeless vegetation of the Australian Alps

A total of 128 invasive plant species have been recorded in treeless vegetation in the Australian Alps. Most of these are forbs and most are uncommon. Cover of invasive species is generally minimal unless there has been gross disturbance to natural vegetation and soils. Although there is a significantly positive correlation between invasive and native species diversity, suggesting that conditions that allow numerous native species to co-exist also permit more plant invasions, altitude is the most important determinant of invasive species diversity. Only 22 of the 128 species have been recorded above 1800 m. Some plant communities (e.g. those with high pH or relatively nutrient-rich soils), however, seem to be vulnerable to invasions regardless of altitude. Most invasive species appear to have been introduced unintentionally (e.g. as seed attached to vehicles, animals and humans) but a few were introduced to assist with revegetation of disturbed soils and for amenity plantings in ski resorts, and have subsequently established in native vegetation. Treeless communities in the Australian Alps are likely to face increasing pressure from invasive species as a result of global warming and continued introduction of non-native plants to ski resort gardens. Whilst it may be difficult to prevent invasive species of low elevations migrating to higher elevations as temperatures rise, the risk of invasion from garden plants could be minimised through regulation. Non-native plants in ski resort gardens pose a far greater risk than most invasive species currently present in the Alps because they have been chosen for their capacity to survive at high altitudes.     

Geomorphological disturbance affects ecological driving forces and plant turnover along an altitudinal stress gradient on alpine slopes

The altitudinal gradient is considered as a stress gradient for plant species because the development and fitness of plant communities tend to decrease as a result of the extreme environmental conditions present at high elevations. Abiotic factors are predicted to be the primary filter for species assemblage in high alpine areas, influencing biotic interactions through both competition for resources and positive interactions among species. We hypothesised that the relative importance of the ecological driving forces that affect the biotic interactions within plant communities changes along an elevation gradient on alpine debris slopes. We used multiple gradient analyses of 180 vegetation plots along an altitudinal range from ~1,600 to 2,600 m and single 100 m-bands in the Adamello-Presanella Group (Central Alps) to investigate our hypothesis; we measured multiple environmental variables related to different ecological driving forces. Our results illustrate that resource limitations at higher elevations affect not only the shift from competition to facilitation among species. A geomorphological disturbance regime along alpine slopes favours the resilience of the high-altitude species within topographic/geomorphological traps. An understanding of the ecological driving forces and positive interactions as a function of altitude may clarify the mechanisms underlying plant responses to present and future environmental changes.     

Vascular plant diversity and climate change in the upper zone of Sierra Nevada,Spain

Abstract

This study examines the effects of altitudinal, temperature and aspect gradients on vascular plant species richness on mountain tops in Sierra Nevada (Spain) at different spatial scales (1 m² quadrats, plot clusters of 4 m², upper summit area down to the 5-m contour line, entire summit down to the 10-m contour line). The methodology follows the Global Observation Research Initiative in Alpine Environments (GLORIA) programme. Floristic and soil temperature data of eight summits sites in two neighbouring regions of the high part of Sierra Nevada (from 2668 m to 3327 m a.s.l.) were used in this study. In total, 102 taxa were recorded (84 genera; 29 families). The species richness decreased, whereas the proportion of endemic taxa increased with elevation. There were significant linear relationships between species richness and altitude and average soil temperature at each spatial scale. However, there was no significant relationship between species richness and aspect variables. Facing continued climate change, the high-altitude flora of Sierra Nevada is expected to be particularly vulnerable and prone to warming-induced biodiversity losses due to the high proportion of endemic taxa, ranging from 23% at lower elevations up to 67% at higher ones.     

Comparative study of spatial patterns and ecological niches of beetles in two Malaysian mountains elevation gradients

The study of beetle communities is a valuable approach for biogeographical and conservation studies because their species and ecological diversities are very high, and they take different roles in ecosystems. However, beetle macroecology and conservation studies are disproportionately scarce, especially in tropical Asia. The objective of this study is to compare beetle abundance, diversity and species richness along the elevation gradients in two mountains in Peninsular Malaysia. Three passive sampling methods were utilized for beetle sampling with four marked elevation gradients: 500 m, 1000 m, 1500 m and 1800 m. Species richness in Fraser’s Hill was higher at highest elevation, but this value was not-significantly different from these in other elevations, except for the site at 1000 m with significantly lower estimates. Genting Highlands showed a significant decrease in species richness with the increase in elevation, without differences between the higher elevation sites. Pairwise comparison of species richness, Simpson Dominance and Shannon diversity between same elevation sites of Fraser’s Hill and Genting Highlands were all significantly different. The levels of vertical and horizontal colonization have had comparatively different weights in terms of their effect on the pattern of diversity and the integration of the beetle community in these two localities. At Fraser’s Hill, similar conditions at different elevations drives different responses, whereas at Genting Highlands contrasting and different environmental conditions at each elevation, drives different responses. We suggest the potential use of these results for biodiversity conservation in terms of climate variables in accordance with niche patterns.     

Genetic and phenotypic variation,dispersal limitation and reproductive success in the invasive herb Eschscholzia californica along an elevation gradient in central Chile

Background: Reductions of genetic diversity and phenotypic changes in invasive plants are often observed to occur at high elevations. Genetic/phenotypic changes of invasive plants along elevation help to understand mechanisms of the presumed resistance of mountain ecosystems to invasion.

Aims: To assess genetic variability and phenotypic plasticity along an elevation gradient of Eschscholzia californica in the Andes, central Chile.

Methods: Eleven microsatellites were used to describe the genetic structure and the allelic diversity individuals, distributed at three elevations and two sites. We assessed the number of flowers per plant, floral biomass, leaf area, number of leaves, vegetative biomass and plant height of plants at each elevation.

Results: Genetic diversity as genetic structure did not decrease with elevations. Plant height and flower numbers decreased while leaf number and vegetative biomass increased with elevation. The ratio of the number of flowers to vegetative biomass, decreased significantly with elevation.

Conclusions: Strong genetic differences among elevations and similar genetic diversity along elevation do not suggest dispersal limitation to higher elevation. Reduction of reproductive and vegetative traits concomitantly with an increase of the reproductive cost suggests reproductive stress with increasing elevation, reducing the invasiveness of this species to higher elevation.     

Current and future distributions of Espeletiinae (Asteraceae) in the Venezuelan Andes based on statistical downscaling of climatic variables and niche modelling

ABSTRACT

Background: Páramos are the high-elevation ecosystems of the humid tropical Andes, characterised by the presence of giant rosettes of the Espeletiinae subtribe (Asteraceae). Forecasted climate change is likely to reduce the extent of the area climatically suitable/occupied currently by Espeletiinae and their elevation distribution patterns.

Aims: The aim of this study was to estimate the potential impacts of forecasted climate change on the geographic distribution (extent of area and elevation distribution patterns) of 28 species of Espeletiinae that have been recorded in the Cordillera de Mérida, Venezuela.

Methods: Six bioclimatic variables, downscaled to a 90 m × 90 m cell size, were used to construct species distribution models (SDM) for the 28 species to model their current and likely future distribution (2070) by using two general circulation models and four representative concentration pathways (RCP).

Results: Nine species were estimated to have potential distribution over less than 1000 km² and five over less than 500 km², in current climatic conditions. Fifteen and eight species had elevation spans narrower than 1000 m and 500 m, respectively. No significant differences in modelled areas or spans were detected between north, central and south sections of the Cordillera de Mérida. Mean ± SE future reduction in the extent of area climatically suitable were estimated between 51.3% ± 6.3% (RCP2.6) and 78.1% ± 5.3% (RCP8.5), coupled with upward range retreat of between 277.8 m ± 27.4 m (RCP2.6) and 762.5 m ± 59.8 m (RCP8.5).

Conclusions: Our study predicts large reductions in modelled area and important upward shifts in the distribution of Venezuelan Espeletiinae by 2070 compared to their current distribution.     

Spatial and temporal dynamics of a freshwater eukaryotic plankton community revealed via 18S rRNA gene metabarcoding

The Brazilian Environmental Ministry (MMA) released a report in 2016 listing 163 non-native species into Brazilian inland waters. Reservoirs are among the freshwater habitats most frequently associated with the release of non-native species. Therefore, the aim of the present study was to evaluate the occurrence and distribution of the non-native species listed by the MMA, in large Brazilian reservoirs (≥ 30 km²). Further, we have tested the hypothesis that beta diversity of non-native species within reservoirs from the same basin is lower than those among reservoirs from distinct basins. A literature search was performed for 70 Brazilian reservoirs, resulting in the records of 91 non-native species. Reservoirs from the Paraná basin showed the highest number of occurrences, with 33 non-native species recorded only in the Itaipu reservoir. Beta diversity of non-native species showed higher variability among reservoirs from different basins than those within the same basin. Some basins were also distinguished by their composition of non-native species, as supported by the IndVal index. Non-native species were widespread along Brazilian reservoirs, and their distribution can be even higher than reported.     

Non-native Fish Occurrence and Biomass in 1943 Western Palearctic Lakes and Reservoirs and their Abiotic and Biotic Correlates

Invasion of non-native species is considered a major threat to global biodiversity. Here we present a comprehensive overview of the occurrence, richness and biomass contribution of non-native fish species in 1943 standing water bodies from 14 countries of the Western Palearctic, based on standardised fish catches by multi-mesh gillnetting. We expected strong geographical gradients to emerge in the occurrence of non-natives. We further hypothesised that the contribution by non-natives to the local fish community biomass was correlated with local richness and the trophic level of native and non-native species. Non-native fish species occurred in 304 of 1943 water bodies (16%). If the average number of occupied water bodies per country was weighted by number of water bodies per country, the grand mean occurrence of non-natives in Western Palearctic water bodies was 10%. Exotic (non-native to the Palearctic) and translocated (non-native only to parts of the Palearctic) species were found in 164 (8.4%) or 235 (12.1%) of the water bodies, respectively. The occurrence and local richness of non-native fish species increased with temperature, precipitation and lake area and were substantially higher in reservoirs than in natural lakes. High local biomass contributions of non-native species were strongly correlated with low richness of native species and high richness of non-native species, whereas the trophic level of the fish species had only a weak effect. Single non-native species rarely dominated community biomass, but high biomass contributions and thus strong community and ecosystem impacts can be expected if several non-native species accumulate in a water body.     

Non-native species and lake warming negatively affect Arctic char Salvelinus alpinus abundance; deep thermal refugia facilitate co-existence

This study finds that non-native species and warming temperatures have significant negative effects on Arctic char Salvelinus alpinus abundance in Irish lakes. Eutrophication was not important at the range of total phosphorus tested (0.005–0.023 mg l⁻¹). Model results predict that S. alpinus occur across the temperature range sampled (8.2–19.7°C) when non-natives are absent, but S. alpinus catch is predicted to be close to zero irrespective of temperature when non-native catch is high. This result indicates that to persist, S. alpinus may require a habitat where non-natives are at low abundance or absent. Salvelinus alpinus segregated from other species along the thermal axis, inhabiting significantly colder water and actively avoided non-native species, which appeared to limit their distribution. The thermal niche realized by S. alpinus in non-native dominated lakes was thus compressed relative to native dominated lakes and S. alpinus population density was significantly lower. These findings were consistent even when the only non-native present was Perca fluviatilis. Temperature appeared to limit the distribution of non-native species, such that the presence of deep thermal refugia is currently facilitating S. alpinus co-existence with non-natives in associated lakes. Diet analysis identified P. fluviatilis as potential predators and competitors. This study provides strong evidence that non-native species are a key driver of low S. alpinus abundance in Irish lakes. Temperature increases associated with climate change are identified as a secondary concern, as they could erode S. alpinus' thermal niche and lead to their extirpation. The lower thermal buffering capacity of shallow lakes identifies these as higher risk systems. Salvelinus alpinus conservation in Ireland should focus on preventing future illegal non-native species introductions because unlike other stressors (e.g., eutrophication etc.), species introductions are rarely reversible.     

Genetically based differentiation in growth of multiple non-native plant species along a steep environmental gradient

A non-native plant species spreading along an environmental gradient may need to adjust its growth to the prevailing conditions that it encounters by a combination of phenotypic plasticity and genetic adaptation. There have been several studies of how non-native species respond to changing environmental conditions along latitudinal gradients, but much less is known about elevational gradients. We conducted a climate chamber experiment to investigate plastic and genetically based growth responses of 13 herbaceous non-native plants along an elevational gradient from 100 to 2,000?m a.s.l. in Tenerife. Conditions in the field ranged from high anthropogenic disturbance but generally favourable temperatures for plant growth in the lower half of the gradient, to low disturbance but much cooler conditions in the upper half. We collected seed from low, mid and high elevations and grew them in climate chambers under the characteristic temperatures at these three elevations. Growth of all species was reduced under lower temperatures along both halves of the gradient. We found consistent genetically based differences in growth over the upper elevational gradient, with plants from high-elevation sites growing more slowly than those from mid-elevation ones, while the pattern in the lower part of the gradient was more mixed. Our data suggest that many non-native plants might respond to climate along elevational gradients by genetically based changes in key traits, especially at higher elevations where low temperatures probably impose a stronger selection pressure. At lower elevations, where anthropogenic influences are greater, higher gene flow and frequent disturbance might favour genotypes with broad ecological amplitudes. Thus the importance of evolutionary processes for invasion success is likely to be context-dependent.     

Constant tree species richness along an elevational gradient of Mt. Bokor,a table-shaped mountain in southwestern Cambodia

Some previous studies along an elevational gradient on a tropical mountain documented that plant species richness decreases with increasing elevation. However, most of studies did not attempt to standardize the amount of sampling effort. In this paper, we employed a standardized sampling effort to study tree species richness along an elevational gradient on Mt. Bokor, a table-shaped mountain in southwestern Cambodia, and examined relationships between tree species richness and environmental factors. We used two methods to record tree species richness: first, we recorded trees taller than 4 m in 20 uniform plots (5 × 100 m) placed at 266–1048-m elevation; and second, we collected specimens along an elevational gradient from 200 to 1048 m. For both datasets, we applied rarefaction and a Chao1 estimator to standardize the sampling efforts. A generalized linear model (GLM) was used to test the relationship of species richness with elevation. We recorded 308 tree species from 20 plots and 389 tree species from the general collections. Species richness observed in 20 plots had a weak but non-significant correlation with elevation. Species richness estimated by rarefaction or Chao1 from both data sets also showed no significant correlations with elevation. Unlike many previous studies, tree species richness was nearly constant along the elevational gradient of Mt. Bokor where temperature and precipitation are expected to vary. We suggest that the table-shaped landscape of Mt. Bokor, where elevational interval areas do not significantly change between 200 and 900 m, may be a determinant of this constant species richness.     

Nutrient limitation in rainforests and cloud forests along a 3,000-m elevation gradient in the Peruvian Andes

We report results from a large-scale nutrient fertilization experiment along a “megadiverse” (154 unique species were included in the study) 3,000-m elevation transect in the Peruvian Andes and adjacent lowland Amazonia. Our objectives were to test if nitrogen (N) and phosphorus (P) limitation shift along this elevation gradient, and to determine how an alleviation of nutrient limitation would manifest in ecosystem changes. Tree height decreased with increasing elevation, but leaf area index (LAI) and diameter at breast height (DBH) did not vary with elevation. Leaf N:P decreased with increasing elevation (from 24 at 200 m to 11 at 3,000 m), suggesting increased N limitation and decreased P limitation with increasing elevation. After 4 years of fertilization (N, P, N + P), plots at the lowland site (200 m) fertilized with N + P showed greater relative growth rates in DBH than did the control plots; no significant differences were evident at the 1,000 m site, and plots fertilized with N at the highest elevation sites (1,500, 3,000 m) showed greater relative growth rates in DBH than did the control plots, again suggesting increased N constraint with elevation. Across elevations in general N fertilization led to an increase in microbial respiration, while P and N + P addition led to an increase in root respiration and corresponding decrease in hyphal respiration. There was no significant canopy response (LAI, leaf nutrients) to fertilization, suggesting that photosynthetic capacity was not N or P limited in these ecosystems. In sum, our study significantly advances ecological understanding of nutrient cycling and ecosystem response in a region where our collective knowledge and data are sparse: we demonstrate N limitation in high elevation tropical montane forests, N and P co-limitation in lowland Amazonia, and a nutrient limitation response manifested not in canopy changes, but rather in stem and belowground changes.     

Invasive Temperate Species are a Threat to Tropical Island Biodiversity

To protect the remaining biodiversity on tropical islands it is important to predict the elevational ranges of non-native species. We evaluated two hypotheses by examining land snail faunas on the eastern (windward) side of the island of Hawaii: (1) the latitude of a species' native region can be used to predict its potential elevational range and (2) non-native temperate species, which experience greater climatic fluctuations in their native range, are more likely to become established at higher elevations and to extend over larger elevational ranges than non-native tropical species. All non-native tropical species were distributed patchily among sites ≤500 m and occupied small elevational ranges, whereas species introduced from temperate regions occupied wide elevational ranges and formed a distinct fauna spanning elevations 500–2000 m. Most native land snail species and ecosystems occur >500 m in areas dominated by temperate non-native snail and slug species. Therefore, knowing the native latitudinal region of a non-native species is important for conservation of tropical island ecosystems because it can be translated into potential elevational range if those species are introduced. Because temperate species will survive in tropical locales particularly at high elevation, on many tropical islands the last refuges of the native species, preventing introduction of temperate species should be a conservation priority.