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Biological invasions are a growing threat to biodiversity. The control and eradication of exotic species established in earnest are of limited success despite high financial investments. Anticipating biological invasions based on species’ suitabilities is a cost-effective strategy given it helps identifying areas where exotic species can prosper, which can then translate in improving management and conservation efforts. Based on information from 191 invasive angiosperm species worldwide, we used ecological niche models to identify areas at high risk of invasion (cumulative predicted distribution of invasive species) in Mexico. Further, we explored the importance of bioclimatic and human influence variables as drivers of the distribution of invasive species and analyzed the status of the currently recognized priority conservation sites in Mexico. We found that areas with intermediate human activity scores had a high risk of invasion. Additionally, we found that many of the current priority conservation sites in Mexico had a high risk of invasion. Our findings contribute to disentangling the factors that drive environment susceptibility to invasions and urge management strategies to minimize the impacts of biological invasions in priority conservation sites.

Global biodiversity and land conservation initiatives rely on an accurate understanding of the spatial distribution of species populations and communities. Identifying the spatial habitat use of wildlife communities across land uses and levels of human modification provides the opportunity to produce more efficient and effectual conservation plans. Our goal was to model breeding bird community occupancy across a complete spectrum of human land use modification to determine the habitat characteristics that best maximized the conservation of bird diversity. We used repeat-visit point counts on private and public lands to record the detection/non-detection of breeding bird species across the land use gradient. We modeled multiple proportional land cover and landscape structure covariates and employed a hierarchical multi-species occupancy model to analyze the habitat use of each species and to estimate guild-level species richness dynamics across the study area. We detected a total of 70 breeding bird species and our model estimated a total of 78 species within the total metacommunity. We found that insectivorous species richness was lowest in urban and suburban areas (xˆ = 7), but highest on multiple use working lands with low to moderate levels of human modification (xˆ = 22), not in the fully preserved protected areas (xˆ = 16). In contrast, the richness of the predominately human commensal omnivorous species was highest in urban and suburban areas (xˆ = 10) and across much of the more human modified landscape and lowest in the preserved lands (xˆ = 3). Moderately disturbed working lands, which primarily consisted of a mixture of rotating silvicultural tracts, agriculture, low density housing, and riparian corridors, supported the most species (xˆ = 36) and were especially important for the occupancy of breeding neotropical insectivores. These findings highlight the potential conservation benefits for incorporating private working lands with multiple land uses and land covers into future conservation planning scenarios, both for their wildlife conservation potential and as buffers around traditional protected areas.

• Exotic angiosperms represent an important threat to Mexican biodiversity. • Angiosperm invasion risk is higher at intermediate values of human influence. • Sites with high and extreme conservation priority in Mexico are at higher risk of invasion by angiosperms. • Models of ecological niche and its internal structure are useful to assess angiosperm invasion risk. Biological invasions are a growing threat to biodiversity. The control and eradication of exotic species established in earnest are of limited success despite high financial investments. Anticipating biological invasions based on species' suitabilities is a cost-effective strategy given it helps identifying areas where exotic species can prosper, which can then translate in improving management and conservation efforts. Based on information from 191 invasive angiosperm species worldwide, we used ecological niche models to identify areas at high risk of invasion (cumulative predicted distribution of invasive species) in Mexico. Further, we explored the importance of bioclimatic and human influence variables as drivers of the distribution of invasive species and analyzed the status of the currently recognized priority conservation sites in Mexico. We found that areas with intermediate human activity scores had a high risk of invasion. Additionally, we found that many of the current priority conservation sites in Mexico had a high risk of invasion. Our findings contribute to disentangling the factors that drive environment susceptibility to invasions and urge management strategies to minimize the impacts of biological invasions in priority conservation sites. [ABSTRACT FROM AUTHOR]

Rhodoliths are round calcareous red algae that form extensive beds and associated with them are a diverse suite of species. Rhodolith beds are among the least known coastal–marine ecosystems, and even less is understood about their associated flora and fauna. Here, we present an evaluation of the biodiversity larger than 500 μm associated with rhodoliths at Isla del Coco National Park, Costa Rica, an oceanic island in the Eastern Tropical Pacific, 500 km offshore of the mainland. This research determined the influence of rhodolith degree of aggregation (distance among individual rhodolith) as well as rhodolith complexity, volume, and mass in relation to the diversity, composition, and biomass of the associated fauna. A total of 145 taxa were collected in 60 rhodolith samples. Arthropods, polychaetes, and mollusks were the dominant taxa in terms of richness, and crustaceans + acari represented >50% of the total abundance. Five potentially new species were collected in this study. Collections identified 31 new records, with 20 of them being newly reported genera for Isla del Coco. Many of the organisms found were juveniles as well as adult stages bearing eggs, demonstrating the importance of this ecosystem. The faunal composition changed along the gradient of rhodolith aggregation. Moderately aggregated rhodoliths (separated by 5 to 10 cm) had the highest diversity, with the highest averages of taxon richness and total numerical abundance and the highest faunal biomass. There were more organisms in more complex rhodoliths; nevertheless, the complexity of the rhodolith did not affect the number of taxa or total organism biomass. Larger rhodoliths, in size and mass, favored higher amounts of taxa and organisms. The rhodolith bed studied is an example of the intermediate disturbance hypothesis because the highest value of biodiversity of invertebrates was at the moderate aggregation level of rhodoliths. In this density of rhodoliths, the fauna was less exposed to hard environmental conditions and prevented dominant species.

The degree to which biotic communities are regionally enriched or locally saturated, and roles of key structuring processes, remain enduring ecological questions. Prior studies of reef-building corals of the Indo-West Pacific (IWP) found consistent evidence of regional enrichment, a finding subsequently questioned on methodological grounds. Here we revisit this relation and associated relations between richness and abundance (as “effective number of species”), and coral cover, used as a proxy for disturbance and competition. From 1994 to 2017, we sampled > 2,900 sites on shallow (typically < 8–10 m depth below reef crest) and deeper reef slopes in 26 coral ecoregions, from Arabia to the Coral Triangle, Eastern Australia, Micronesia and Fiji, for a total pool of 672 species. Sampling intensity varied among ecoregions but always approached asymptotic richness. Local coral communities on both shallow and deep reef slopes were, on average, comprised of 25% of regional pools, ranging from 12 to 43% for individual ecoregions. The richest individual shallow and deep sites, averaged across all ecoregions, comprised 42 and 40% of regional pools, ranging from 30 to 60%, the highest in environmentally marginal ecoregions. Analyses using log-ratio regression indicated that IWP coral communities on deeper reef slopes were intermediate between regionally enriched and locally saturated. Communities on shallow reef slopes showed more evidence of regional enrichment, consistent with these being most susceptible to disturbance. Unimodal curvilinear relations between local richness and coral cover provide support for disturbance mediation and competitive exclusion. IWP coral communities are clearly dynamic, shaped by biological, ecological, and oceanographic processes and disturbance regimes that influence reproduction, dispersal, recruitment, and survival. Yet there is also evidence for a degree of local saturation, consistent with a niche-neutral model of community assembly. The richest sites hosted > 200 species, > 40% of regional pools and > 25% of the IWP total. These places may represent the asymptote of local richness in reef-building corals, rare examples of the ecological complexity for which these increasingly endangered communities are justly renowned.

Anthropogenic land transformation is a consequence of human population growth and the associated agricultural, residential, and industrial needs. This study aimed to investigate the effects of anthropogenic activity and human-mediated land transformation on capture/recapture frequencies, species richness, and diversity of native small mammal community assemblages in the Magaliesberg Biosphere, North West province, South Africa. Five anthropogenically transformed land-use types were investigated: an animal rehabilitation and ecotourism center, an agricultural farmstead, a residential farmstead, a mine-adjacent agricultural farmstead, and a protected nature conservancy. We used live traps to sample small mammals during the dry and wet seasons over three consecutive years and compared population numbers and species composition across study sites and seasons. Capture/recapture frequencies differed significantly between sites and seasons, with the highest capture frequencies recorded at the agricultural and residential farmsteads. Species richness and diversity were highest at the residential and mine-adjacent farmsteads, both of which experienced intermediate levels of anthropogenic disturbance throughout the sampling period. The study shows that while natural and protected landscapes with low levels of disturbance are preferred, transformed landscapes can also be managed effectively to benefit native small mammal populations by regulating the frequency and intensity of human-mediated activities.

Water mites are important constituents of aquatic ecosystems, but their biodiversity is poorly understood. The goal of this study was to improve knowledge of water mite assemblages in the Detroit River through combined use of morphological and cytochrome oxidase I (COI) DNA barcode data and to elucidate seasonal water mite diversity. The diversity of water mites collected from Blue Heron Lagoon at Belle Isle, an island in the Detroit River, is described. Novel DNA barcodes for Albia, Hydrochoreutes, Madawaska, and Axonopsis are reported with a species level barcode for Lebertia. Novel DNA barcodes may represent the presence of previously undescribed variants or new species of several genera. The prevalence of water mites is higher in the summer, but a different pattern is observed for diversity. The diversity of water mites, by several measures, varies seasonally with lower diversity in summer and winter months and higher diversity during seasonal transitions. For these organisms, we interpret seasonal change as an intermediate disturbance resulting in increased biodiversity. [ABSTRACT FROM AUTHOR]

Forests play an integral role in the terrestrial water cycle and link exchanges of water between the land surface and the atmosphere. To examine the effects of an intermediate disturbance on forest water cycling, we compared vertical profiles of stable water vapor isotopes in two closely located forest sites in northern lower Michigan. At one site, all canopy‐dominant early successional species were stem girdled to induce mortality and accelerate senescence. At both sites, we measured the isotopic composition of atmospheric water vapor at six heights during three seasons (spring, summer, and fall) and paired vertical isotope profiles with local meteorology and sap flux. Disturbance had a substantial impact on local water cycling. The undisturbed canopy was moister, retained more transpired vapor, and at times was poorly mixed with the free atmosphere above the canopy. Differences between the disturbed and undisturbed sites were most pronounced in the summer when transpiration was high. Differences in forest structure at the two sites also led to more isotopically stratified vapor within the undisturbed canopy. Our findings suggest that intermediate disturbance may increase mixing between the surface layer and above‐canopy atmosphere and alter ecosystem‐atmosphere gas exchange. Plain Language Summary: Forests play an important role in the climate system and link water fluxes between the land surface and the atmosphere. Here we compare water vapor isotopes in two adjacent forest sites in the northern lower peninsula of Michigan to understand the effects of intermediate disturbance and canopy structure on forest water cycling. One site is dominated by aspen and birch and has a thick, closed canopy. All of the aspen and birch were killed at the second site. As a result, the disturbed site has a more open‐canopy structure. From our comparison, we found that both the species of tree and the spacing around trees are important controls on forest water cycling. With more space between trees, air mixes more freely into the canopy, which dries the forest air. Alternatively, air may be poorly mixed within and above thick, closed canopies. Key Points: Intermediate disturbance can change the contribution of entrained, evaporated, and transpired water vapor to forest canopiesCanopy gaps increase hydrologic mixing between the surface layer and the free atmosphereThe assumption of a well‐mixed canopy atmosphere may be violated in the case of thick, homogeneous forest canopies [ABSTRACT FROM AUTHOR]

The biotic resistance hypothesis (BRH) was proposed to explain why intermediate disturbances lead to greater resistance to non-native invasions proposing communities that are more diverse provide greater resistance. However, several empirical data sets have rejected the BRH because native and non-native species richness often have a positive relation. We tested the BRH in a mature loblolly pine (Pinus taeda) forest with a gradient of disturbance intensities including canopy reduction, canopy reduction + fire, and canopy reduction + herbicide and fire. We analyzed data from the study using a combination of Pearson's correlation and beta regressions. Using species richness, we too would reject BRH because of a positive correlation in species richness between native and non-native plants. However, native species abundance was greatest, and non-native species abundance was lowest following intermediate disturbances. Further, native and non-native species abundances were negatively correlated in a quadratic relation across disturbance intensities, suggesting that native species abundance, rather than richness, may be the mechanism of resistance to non-native invasions. We propose that native species abundance regulates resistance to non-native invasions and that intermediate disturbances provide the greatest resistance because they promote the greatest native species abundance. [ABSTRACT FROM AUTHOR]

An increasing number of international initiatives aim to reconcile development with conservation. Crucial to successful implementation of these initiatives is a comprehensive understanding of the current ecological condition of landscapes and their spatial distributions. Here, we provide a cumulative measure of human modification of terrestrial lands based on modeling the physical extents of 13 anthropogenic stressors and their estimated impacts using spatially explicit global datasets with a median year of 2016. We quantified the degree of land modification and the amount and spatial configuration of low modified lands (i.e., natural areas relatively free from human alteration) across all ecoregions and biomes. We identified that fewer unmodified lands remain than previously reported and that most of the world is in a state of intermediate modification, with 52% of ecoregions classified as moderately modified. Given that these moderately modified ecoregions fall within critical land use thresholds, we propose that they warrant elevated attention and require proactive spatial planning to maintain biodiversity and ecosystem function before important environmental values are lost. Several international initiatives aim to balance development with conservation goals, which requires a comprehensive understanding of the current ecological condition of landscapes. We quantified the spatial extent and pattern of human land modification using a cumulative measure of 13 anthropogenic stressors with median year of 2016. We identified that fewer unmodified lands remain than previously reported and that most of the world's ecoregions fall at critical land modification thresholds, thus, warrant timely conservation attention. [ABSTRACT FROM AUTHOR]

We studied vegetation attributes in Indian tropical moist deciduous unmanaged forests to determine the influence of forest disturbances on them. We enumerated 89 species: 72 under moderate disturbance and 54 under least disturbance. The data from 3399 stems [>5 cm diameter at breast height (dbh)] decreased linearly along the disturbance gradient. The basal area was largest in least disturbed forests (61 m2/ha) and smallest in intensely disturbed forest (41 m2/ha). Under least and moderate disturbance, tree density-diameter distribution had negative exponential curves, whereas highly disturbed forests had unimodal-shaped curves where a few trees 5–10 cm and >50 cm in diameter were recorded. Most tree and shrub layer species under heavy and intense disturbance had impaired regeneration. Moderate disturbance intensity thus apparently benefits species diversity, stand density, and regeneration. Decline in seedlings and saplings, especially tree species, threaten forest regeneration and the maintenance of species diversity of unmanaged tropical forests.

Abstract: The plateau pika (Ochotona curzoniae) is known to influence the plant diversity and biomass of the alpine meadow, and it is regarded as a pest. The species has been subject to extensive controls without a clear target density in the Qinghai‐Tibetan Plateau. We investigated the effects of different plateau pika disturbance levels on plant composition, species diversity and biomass. The density of active burrow entrances was used as an index of disturbance levels I, II, III and IV (corresponding to 8, 19, 27 and 39 active burrow entrances per 625 m2). We found that the plant community composition differed with different disturbance levels. The plant replacements were mainly related to associate plants rather than dominant plants. With the increase in the plateau pika disturbance levels, the plant cover decreased, and the plant height first increased and then decreased. The plant evenness index was higher in the levels II and III disturbance conditions, while the plant diversity index and plant richness index were highest in the level IV disturbance condition. The disturbance levels had no effect on the total plant biomass; however, the intermediate disturbance levels (II and III) increased the palatable plant biomass. The total plant biomass was mainly dependent on the unpalatable plant biomass. The total plant biomass showed a positive correlation with the richness index and a negative correlation with the evenness index. The palatable plant biomass showed a positive correlation with the evenness index and a negative correlation with the richness index. These results imply that the intermediate disturbance levels are beneficial to livestock production as they increase the alpine meadow quality, and the higher disturbance level is better for plant diversity conservation in the alpine meadows of the Qinghai‐Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Abstract: Wind is one of the most important natural disturbances influencing forest structure, ecosystem function, and successional processes worldwide. This study quantifies the stand‐scale effects of intermediate‐severity windstorms (i.e., blowdowns) on (1) live and dead legacy structure, (2) aboveground carbon storage, and (3) tree regeneration and associated stand dynamics at four mature, mixed hardwood–conifer forest sites in the northeastern United States. We compare wind‐affected forests to adjacent reference conditions (i.e., undisturbed portions of the same stands) 0–8 yr post‐blowdown using parametric (ANOVA) and nonparametric (NMS ordination) analyses. We supplement inventory plots and downed coarse woody detritus (DCWD) transects with hemispherical photography to capture spatial variation in the light environment. Although recent blowdowns transferred a substantial proportion of live overstory trees to DCWD, residual live tree basal area was high (19–59% of reference areas). On average, the initial post‐blowdown ratio of DCWD carbon to standing live tree carbon was 2.72 in blowdown stands and 0.18 in reference stands, indicating a large carbon transfer from live to dead pools. Despite these dramatic changes, structural complexity remained high in blowdown areas, as indicated by the size and species distributions of overstory trees, abundance of sound and rotten downed wood, spatial patterns of light availability, and variability of understory vegetation. Furthermore, tree species composition was similar between blowdown and reference areas at each site, with generally shade‐tolerant species dominating across multiple canopy strata. Community response to intermediate‐severity blowdown at these sites suggests a dynamic in which disturbance maintains late‐successional species composition rather than providing a regeneration opportunity for shade‐intolerant, pioneer species. Our findings suggest that intermediate‐severity wind disturbances can contribute to stand‐scale structural complexity as well as development toward late‐successional species composition, at least when shade‐tolerant regeneration is present pre‐blowdown. Advance regeneration thus enhances structural and compositional resilience to this type of disturbance. This study provides a baseline for multi‐cohort silvicultural systems designed to restore heterogeneity associated with natural disturbance dynamics. [ABSTRACT FROM AUTHOR]

Beta diversity can provide insights into the processes that regulate communities subjected to frequent disturbances, such as flood pulses, which control biodiversity in floodplains. However, little is known about which processes structure beta diversity of amphibians in floodplains. Here, we tested the influence of flood pulses on the richness, composition, and beta diversity of amphibians in Amazonian floodplain environments. We also evaluated indicator species for each environment. We established linear transects in three environments: low várzea, high várzea, and macrophyte rafts. Species richness decreased and beta diversity increased according to the susceptibility of habitats to flood pulses. Indicator species differed among environments according to forest succession promoted by the flood pulse. The decrease in species richness between high and low várzea is due to non-random extinctions. The higher rates of species turnover between várzeas and macrophyte rafts are driven by the colonization of species adapted to open areas. Our results highlight that the maintenance of complex environments is needed to protect biodiversity in floodplains. [ABSTRACT FROM AUTHOR]

The perturbation of Neotropical forests generates large disturbances in biological communities. The species that suffer least from the resulting habitat fragmentation are the pioneers, because they possess greater ability to inhabit disturbed environments. Therefore, it is expected that species diversity will be greater in areas subjected to intermediate disturbance, such as the opening of gaps, because a large number of pioneer species will develop and coexist with species of more advanced successional stages. This study aimed to compare two forest remnants that differed in size and disturbance intensity, in order to determine the effects of disturbances on species diversity and the size ratios of individual trees. This was accomplished with comparative analyses of diversity, richness and diameter ratios obtained for 10 plots at two semideciduous forest sites. We recorded a total of 85 species, of which 70 were in the private nature reserve Fazenda Santa Maria, 58 were in Iguaçu National Park, and 43 were at both sites. Diversity was greater in the more disturbed remaining forest, because this area showed higher species richness, which is in accordance with some premises of the intermediate disturbance theory. There was also an increase in the number of pioneer individuals, and the less disturbed area showed individuals with larger diameters, which is likely attributable to the removal of large individuals from the more disturbed area during the anthropogenic process of forest modification.

We quantified damage by a microburst windstorm to a northern hardwood forest (Hubbard Brook Experimental Forest, New Hampshire). These storms may be important in regulating the structure and composition of forests of the northeastern United States, but few studies of damage patterns from microbursts have been reported. In the 600 ha area most heavily impacted by the microburst at Hubbard Brook, 4.6% of the canopy was removed. Although most disturbances were small (<200 m2), much (22%) of the area damaged by the storm was associated with one 5.2 ha blowdown within which 76% of the trees suffered severe damage. Roughly one-half of the damaged trees were uprooted and one-quarter were snapped off, with few differences among tree species. The remaining trees in the blowdown either avoided damage or suffered less severe damage (i.e., leaning but not snapped or uprooted). Regeneration of shade-intolerant (pin cherry ( Prunus pensylvanica L. f.)) and mid-tolerant (yellow birch ( Betula alleghaniensis Britt.), red maple ( Acer rubrum L.)) trees was present in the large canopy gaps. While recruitment opportunities in these large gaps may be important for maintaining populations of pioneer species, the limited spatial extent of microbursts suggests that they play a minor role in the overall dynamics of the northeastern forest. [ABSTRACT FROM AUTHOR]

To study forest composition and structure, as well as to facilitate management plans and monitoring programs, we conducted a phytosociological survey in the PE Caverna do Diabo State Park and the Quilombos do Médio Ribeira Environmentally Protected Area, both located within the state of São Paulo, Brazil. We analyzed 20 plots of 400 m² each, including only individuals with a circumference at breast height > 15 cm. We employed cluster analysis and ordination (principal component analysis and correspondence analysis), including species data and abiotic data. We evaluated 1051 individuals, belonging to 155 species in 48 families. Of those 155, 18 were threatened species, 33 were endemic species, and 92 (59.4%) were secondary species. The overall Shannon index was 4.524, one of the highest recorded for a dense rainforest in southeastern Brazil. We found that our sample plots fell into three blocks. The first was forest in which there had been human disturbance, showing low species richness, minimal density, and a small relative quantity of biomass. The second was undisturbed mature forest, showing a comparatively larger quantity of biomass. The third was mature forest in which there had been natural intermediate disturbance (dead trees), showing higher species richness and greater density. We identified various groups of species that could be used in monitoring these distinct forest conditions.

Biologists often copewith variation in physiological, environmental and ecological processes by measuring how living systems perform under average conditions. However, performance at average conditions is seldom equal to average performance across a range of conditions. This basic property of nonlinear averaging - known as 'Jensen's inequality' or 'the fallacy of the average' - has important implications for all of biology. For instance, a burgeoning awareness of Jensen's inequality has improved our ability to predict how plants and animals will respond to awarmer andmore variable future climate. But formany biologists, the fallacy of the average is still a novel concept. Here, I highlight the importance of Jensen's inequality, provide a simple graphical approach to understanding its effects, and explore its consequences at atomic, molecular, organismal and ecological levels. [ABSTRACT FROM AUTHOR]

Robert T. Paine, who passed away on 13 June 2016, is among the most influential people in the history of ecology. Paine was an experimentalist, a theoretician, a practitioner, and proponent of the 'ecology of place,' and a deep believer in the importance of natural history to ecological understanding. His scientific legacy grew from the discovery of a link between top-down forcing and species diversity, a breakthrough that led to the ideas of both keystone species and trophic cascades, and to our early understanding of the mosaic nature of biological communities, causes of zonation across physical gradients, and the intermediate-disturbance hypothesis of species diversity. Paine's influence as a mentor was equally important to the growth of ecological thinking, natural resource conservation, and policy. He served ecology as an Ecological Society of America president, an editor of the Society's journals, a member of and contributor to the National Academy of Sciences and the National Research Council, and an in-demand advisor to various state and federal agencies. Paine's broad interests, enthusiasm, charisma, and humor deeply affected our lives and the lives of so many others. [ABSTRACT FROM AUTHOR]

Question Which types of management practice promote plant species richness in semi-natural grasslands? Which environmental factors might be involved in this management effect? How do different plant life-form groups respond to these variables? Location Kaida Plateau, Nagano Prefecture, Japan. Methods In the study area, hay meadows were traditionally maintained through both burning and mowing every second year. Recently, however, meadows that have either been abandoned or maintained only by annual burning or annual mowing have increased. We compared plant species richness, vegetation height and soil pH and water content between traditional meadows and those abandoned or maintained only by burning or mowing. We also examined relationships between these variables and the species richness of plant life-form groups. Results The mean total and rare plant richness (36 and eight species·m−2, respectively) in traditionally managed meadows were higher than in meadows of other management types (<26 and ≤5 species·m−2, respectively). Vegetation height (20-290 cm) and soil pH (4.2-6.2) varied among study plots. Burning and mowing frequencies negatively influenced vegetation height and positively influenced soil pH and/or water content. Traditional management practice provided intermediate vegetation heights (90 cm) and soil pH (5.3). Total species richness showed a unimodal relationship with vegetation height (peaking at 125 cm), and rare species richness was highest at intermediate levels of vegetation height (86 cm) and soil pH (5.2). Conclusions This study demonstrates that intermediate levels of vegetation height and soil pH have been maintained through traditional practices combining both infrequent burning and mowing. These practices are essential for conserving common and rare plant diversity in the study area with oligotrophic soil conditions. [ABSTRACT FROM AUTHOR]

North American temperate forests have functioned as a terrestrial carbon (C) sink for more than a century, but the future of this sink is highly uncertain as disturbance frequency increases and regrown forests approach maturity. The subcanopy is integral to the functional recovery of forests, supporting short-term resilience of primary production and longer-term shifts in tree species composition and diversity. However, the factors that contribute to variation in forest subcanopy response to disturbance are not well understood. In this study, we investigated subcanopy shifts in aboveground wood net primary productivity (ANPP w ) and composition following experimental moderate severity disturbance emulating natural canopy mortality from age-related senescence. We assessed the importance of variation in disturbance severity, site fertility, and community composition on subcanopy disturbance response and contribution to total (canopy and subcanopy) ANPP w response. We also assessed the effect of the moderate severity disturbance on species composition and diversity, and competitive patterns within the subcanopy layer. Subcanopy aboveground biomass and ANPP w increased substantially relative to pre-disturbance levels by a factor of 1.4 and 22.7, respectively. The subcanopy (stems <8 cm DBH) made up a large component of overall (canopy plus subcanopy) post disturbance ANPP w (16.2%) and disturbance response (post-disturbance ANPP w /pre-disturbance ANPP w ; 54.1%). Subcanopy ANPP w , subcanopy post-disturbance ANPP w response, and subcanopy contribution to total post-disturbance ANPP w response were all most strongly predicted by subcanopy community composition in combination with canopy composition and site fertility. Variation in disturbance severity was not a strong predictor of subcanopy ANPP w response to disturbance. Subcanopy compositional trends and growth patterns both indicate likely increased heterogeneity in canopy composition (greater β diversity) and a potential shift toward greater dominance by mid-tolerant Quercus rubra (northern red oak). Our results illustrate the importance of the subcanopy in the response of forest productivity to moderate severity disturbance and illustrate that composition of the subcanopy layer exerts a strong influence on the growth response both of the subcanopy and the forest as a whole. Our findings highlight the unique role of moderate severity disturbance, relative to more severe disturbances, in promoting biological and structural heterogeneity in forest ecosystems and favoring underrepresented mid-tolerant species. [ABSTRACT FROM AUTHOR]

In late successional forests, stand development processes are often more easily monitored and are more closely related to key ecological parameters when using structural criteria rather than stand age or time since stand-replacing disturbance. In this paper, the effects of various disturbance regimes on long-term structural change and resilience in 70 primary northern hardwood stands were analyzed using the CANOPY individual-tree model. Compared to a ‘dichotomous’ disturbance regime of small gap dynamics with infrequent severe disturbance, the historic natural disturbance regime of periodic low- and moderate-severity disturbances produced a more complex landscape mosaic similar to the current landscape. Under the natural disturbance regime, mean residence time in each of 8 structural stages was short (8–35 years) and followed descending monotonic distributions. Mean residence time in old growth was 87 years. Old-growth stands with stable size distributions were much more frequent when defined by relevant structural criteria than when defined by their past history (timing and severity of disturbances). Repeated mild and moderate disturbances often caused stand structure to retrogress to mature or earlier old-growth stages without undergoing stand replacement. However, simulation experiments often demonstrated structural resilience to repeated mild disturbance, even at the 0.5 ha scale. In some cases, disturbances accelerated the development of more complex structure typical of late transition or steady-state stands. Recovery from heavy partial canopy removal was markedly faster than recovery after stand-replacing disturbance. Stands recovered to an old-growth condition with a stable size distribution (‘quasi-steady state’) 175 years after disturbances removing 60% of the aggregate crown area, compared to 280 years after a disturbance with no residual trees. High dominance of these landscapes by old-growth forest (78% of total area) is due not only to the low frequency of stand-replacing disturbance, but also to the structural resilience of old growth to periodic episodes of low- and moderate-severity disturbance. [ABSTRACT FROM AUTHOR]

Although Richardson's Ground Squirrels (Urocitellus richardsonii) are considered pests throughout their North American range, their impact on forage in Canadian aspen parkland has not been explored. We investigated the effect of Richardson's Ground Squirrel density on forage quality and plant community composition in an intensely grazed cattle pasture in the aspen parkland region of Manitoba, Canada. We detected no significant differences in forage protein content or legume, grass, and litter biomass among ground squirrel density levels. However, ground squirrel density did influence the abundance of invasive and forage plant species; greater squirrel density reduced the prevalence of Smooth Brome (Bromtts inermis Leysser) and Red Clover (Trifolium pratense L.) and increased the abundance of Quackgrass (Elymus repens (L.) Gould) and Black Medick (Medicago lupulina L.). Plant community diversity also increased with ground squirrel density. There were no differences in soil bulk density or ammonia content among squirrel density levels; however, soil nitrate content was highest at low ground squirrel density. Changes in available soil nitrogen and relative abundances of forage species on this pasture may affect cattle diet by altering both the availability and quality of forage. Our findings highlight the need for further investigation of the role of Richardson's Ground Squirrel on rangeland in the aspen parkland region to ascertain the generality of the effects documented in our study. Until such effects and their implications for cattle production are understood, land managers should refrain from exterminating colonies of Richardson's Ground Squirrel. [ABSTRACT FROM AUTHOR]

The regrowing forests of eastern North America have been an important global C sink over the past 100+ years, but many are now transitioning into late succession. The consequences of this transition are unclear due to uncertainty around the C dynamics of oldgrowth forests. Canopy structural complexity (CSC) has been shown to be an important source of variability in C dynamics in younger forests (e.g., in productivity and resilience to disturbance), but its role in late-successional forests has not been widely addressed. We investigated patterns of CSC in two old-growth forest landscapes in the Upper Peninsula of Michigan, USA, to assess factors associated with CSC and its influence on productivity and disturbance resilience (to moderate-severity windstorm). CSC was quantified using a portable below-canopy LiDAR (PCL) system in 65 plots that also had long-term (50-70 + years) inventory data, which were used to quantify aboveground net primary productivity (ANPP), disturbance history, and stand characteristics. We found high and variable CSC relative to younger forests across a suite of PCL-derived metrics. Variation in CSC was driven by species composition and size structure, rather than disturbance history or site characteristics. Recent moderate severity wind disturbance decreased plot-scale CSC, but increased stand-scale variation in CSC. The strong positive correlation between CSC and productivity illustrated in younger forests was not present in undisturbed portions of these late-successional ecosystems. Moderate severity disturbance appeared to reestablish the positive link between CSC and productivity, but this relationship was scale and severity dependent. A positive CSCproductivity relationship was evident at the plot scale with low-severity, dispersed disturbance, but only at a patch scale in more severely disturbed areas. CSC does not appear to strongly correlate with variation in productivity in undisturbed old-growth forests, but may play a very important (and scale/severity-dependent) role in their response to disturbance. Understanding potential drivers and consequences of CSC in late-successional forests will inform management focused on promoting complexity and old-growth conditions, and illustrate potential impacts of such treatments on regional C dynamics. [ABSTRACT FROM AUTHOR]

Natural disturbance regimes play key roles in shaping forest structure and development at stand and landscape levels. Disturbances are commonly complex and variable, such that classical dichotomous characterization of disturbance regimes as following large infrequent disturbances or patch dynamics is too simplistic, especially when the resulting damage is more severe than the baseline of a single tree patch dynamic, but not severe enough to represent large infrequent disturbance. Ongoing climate change affects mountain Picea abies forests in Central, East and Southeastern Europe by an increasing frequency of storms and bark beetle outbreaks. We present a unique study based on extensive dataset aimed to reveal the spatiotemporal pattern of the disturbance history and role of the mixed severity disturbances in primary spruce mountain forest landscapes in the Ukrainian Carpathians. We reconstructed canopy disturbance history and maximum disturbance severity using ca. 2396 tree cores in 96 sample plots. Neither large-scale stand-replacement nor fine scale dynamics was the prevailing disturbance over the last four centuries. Rather, we observed a complex spatiotemporal pattern of mixed severity disturbances. Canopy turnover time ranged between 50 and 300 years and depended on the maximum severity of the disturbance event. Spatial analyses revealed no similarity in spatiotemporal pattern across disturbance histories or maximum disturbance severities. We observed evidence of a combination of variable severity disturbances that fails to fit the classical scheme of gap or patch dynamics with sharply defined sizes and borders, but is more consistent with a mixed severity disturbance regime across the landscape. Windstorms were likely the most important past disturbance agent. The probability of an epidemic bark beetle attack was low, although the possibility of small local outbreaks cannot be excluded. An additional, potentially overlooked, agent of disturbance could be historic periods of extreme cold. This reconstructed disturbance regime may challenge existing silvicultural systems in the Carpathians, calling for a more complex spatiotemporal forest management approach. However, mimicking a mixed severity disturbance regime can be done at the forest management level by applying a range of disturbance severities at the stand level. [ABSTRACT FROM AUTHOR]

Studies of conservation in small scale societies typically portray indigenous peoples as either sustainably managing resources, or forsaking long-term sustainability for short-term gains. To explain this variability, we propose an alternative framework derived from a co-evolutionary perspective. In environments with long histories of consistent interaction, we suggest that local species will frequently be well adapted to human disturbance; but where novel interactions are introduced, human disturbance may have negative environmental consequences. To test this co-evolutionary hypothesis, we examine the effect of Aboriginal burning and hunting on hill kangaroo ( Macropus robustus) abundance. We find that hill kangaroo populations peak at intermediate levels of human disturbance, showing that in ecosystems characterized by long-term human-environmental interactions, humans can act as trophic mediators, resulting in patterns consistent with epiphenomenal conservation. Framing the question within this co-evolutionary perspective provides an explanation for the underlying mechanisms that drive environmental outcomes of subsistence practices. [ABSTRACT FROM AUTHOR]

Copyright of Brazilian Journal of Biology is the property of Instituto Internacional de Ecologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

ABSTRACT Dissolved oxygen (DO) concentrations in lowland streams are naturally lower than those in upland streams; however, in some regions where monitoring data are lacking, DO criteria originally established for upland streams have been applied to lowland streams. This study investigated the DO concentrations at which fish and invertebrate assemblages at 35 sites located on lowland streams in southwestern Louisiana began to demonstrate biological thresholds. Average threshold values for taxa richness, diversity and abundance metrics were 2.6 and 2.3 mg/L for the invertebrate and fish assemblages, respectively. These thresholds are approximately twice the DO concentration that some native fish species are capable of tolerating and are comparable with DO criteria that have been recently applied to some coastal streams in Louisiana and Texas. DO minima >2.5 mg/L were favoured for all but extremely tolerant taxa. Extremely tolerant taxa had respiratory adaptations that gave them a competitive advantage, and their success when DO minima were <2 mg/L could be related more to reductions in competition or predation than to DO concentration directly. DO generally had an inverse relation to the amount of agriculture in the buffer area; however, DO concentrations at sites with both low and high amounts of agriculture (including three least-disturbed sites) declined to <2.5 mg/L. Thus, although DO fell below a concentration that was identified as an approximate biological threshold, sources of this condition were sometimes natural (allochthonous material) and had little relation to anthropogenic activity. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Copyright of Revista Biociências is the property of Revista Biociencias and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Shifts in disturbance regime have often been linked to invasion in systems by native and nonnative species. This process can have negative effects on biodiversity and ecosystem function. Degradation may be ameliorated by the reinstatement of the disturbance regimes, such as the reintroduction of fire in pyrogenic systems. Modeling is one method through which potential outcomes of different regimes can be investigated. We created a population model to examine the control of a native invasive that is expanding and increasing in abundance due to suppressed fire. Our model, parameterized with field data from a case study of the tree Allocasuarina huegeliana in Australian sandplain heath, simulated different fire return intervals with and without the additional management effort of mechanical removal of the native invader. Population behavior under the different management options was assessed, and general estimates of potential biodiversity impacts were compared. We found that changes in fire return intervals made no significant difference in the increase and spread of the population. However, decreased fire return intervals did lower densities reached in the simulated heath patch as well as the estimated maximum biodiversity impacts. When simulating both mechanical removal and fire, we found that the effects of removal depended on the return intervals and the strategy used. Increase rates were not significantly affected by any removal strategy. However, we found that removal, particularly over the whole patch rather than focusing on satellite populations, could decrease average and maximum densities reached and thus decrease the predicted biodiversity impacts. Our simulation model shows that disturbance-based management has the potential to control native invasion in cases where shifted disturbance is the likely driver of the invasion. The increased knowledge gained through the modeling methods outlined can inform management decisions in fire regime planning that takes into consideration control of an invasive species. Although particularly applicable to native invasives, when properly informed by empirical knowledge these techniques can be expanded to management of invasion by nonnative species, either by restoring historic disturbance regimes or by instating novel regimes in innovative ways. [ABSTRACT FROM AUTHOR]

Why competitive exclusion does not limit the number of coexisting plankton species is a persistent question for community ecology. One explanation, the intermediate disturbance hypothesis (IDH), proposes that elevated species diversity is a product of moderate levels of disturbance that allow the subsequent invasion of less competitive species. Here, we assess the shifts in species diversity in a mysid ( Mysidae Dana, 1850) zooplankton community, where at least 10 species have, over the last 15 years, have come to comprise the primary prey base of summer resident gray whales ( Eschrictius robustus Lilljeborg, 1861) in Clayoquot Sound, British Columbia. We evaluate trends in the community structure of mysids (species dominance, diversity, and richness) across mysid habitat in the study area during the gray whale foraging season (May-September) for the period 1996 and 2008. Mysid species composition varies among years and diversity has increased as whales shifted their predatory focus from benthic amphipods ( Ampeliscidae Costa, 1857) to mysids, near our starting point in 1996. Holmesimysis sculpta Tattersall, 1933 was the dominant species in early years; however, in 2007, the dominance shifted to Neomysis rayi Murdoch, 1885. The habitat restrictions and life history attributes of local populations of coastal mysids leave them vulnerable to the cumulative impacts of increased predation pressure by gray whales. This case study presents a unique examination implicating predation as an agent of disturbance capable of altering the species structure of a local prey community. [ABSTRACT FROM AUTHOR]

The article presents the before-after control-impact study on the effect of prescribed burns and a wildlife on the alpha and beta diversity of lizards, mammals and plants in hummock grassland in arid central Australia. The study applies the intermediate disturbance (IDH) and patch mosaic burn (PMBH) to predict that small-scale, patchy, prescribed burns would increase the alpha diversity. It is concluded that prescribed fire is of little utility for the broadscale conservation of biodiversity.

The Gemenc floodplain of the Danube possesses numerous side arms and backwaters. The aim of my study was to explore connections between hydrological events and diversity patterns of the planktonic rotifer assemblages of these water bodies. During the study period (2002-2008) 75 taxa of rotifers were found. Generally, the water bodies of the floodplain had more diverse rotifer assemblages than the main arm. At low and medium water levels diversity was highest in the parapotamal water bodies. This result may be explained by the intermediate disturbance hypothesis. At high water levels the highest biodiversities shifted to the plesiopotamal. Biodiversity, dominance, and evenness correlated with water flow and temperature. Patterns of biodiversity seem to be determined by the water level of the main arm; therefore the water regime appears to provide pronounced temporal variability in the hydro-ecology of the floodplain. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

What maintains plant species diversity has been the subject of much debate with no general consensus. In forest ecosystems in which understory plants account for the majority of floristic diversity, a crucial question is whether understory plant diversity is driven by resource quantity or resource heterogeneity. This study sought to reconcile the two hypotheses in relation to their effects on understory plant diversity in forest ecosystems. A database of studies that investigated the effects of resources on understory plant diversity was compiled and analyzed using log-linear models. Whether resource quantity or resource heterogeneity is the determinant of understory plant diversity in individual studies was dependent on stand successional stage(s), presence or absence of intermediate disturbance, and forest biome within which the studies were conducted. Resource quantity was found to govern species diversity in both young and mature stands, whereas resource heterogeneity dominated in old-growth stands. Resource quantity remained the important driver in both disturbed and undisturbed forests, but resource heterogeneity played an important role in disturbed forests. We argue that neither resource quantity nor heterogeneity alone structures species diversity in forest ecosystems, but rather their influences on understory plant diversity vary with stand development and disturbances in forest ecosystems. [ABSTRACT FROM AUTHOR]

Copyright of Neotropical Biology & Conservation is the property of Pensoft Publishers and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The article presents a study which investigates the impact of ski-caused disturbance on the properties of ecosystem in Sierra Nevada in California and Nevada. The study examined soil, vegetation and environmental characteristics on forests adjacent to downhill ski resorts. It shows that bigger disturbance intensity related to grading yielded huge effect on all ecosystem properties including the composition and diversity of plant community, soil characteristics and nutrient retention and cycling.

Litter-nesting ants are diverse and abundant in tropical forests, but the factors structuring their communities are poorly known. Here we present results of the first study to examine the impact of natural variation in flooding on a highly diverse (21 genera, 77 species) litter-nesting ant community in a primary Amazonian forest. Fifty-six 3 × 3 m plots experiencing strong variation in flooding and twenty-eight 3 × 3 m terra firme plots were exhaustively searched for litter-nesting ants to determine patterns of density, species richness and species composition. In each plot, flooding, litter depth, twig availability, canopy cover, plant density, percent soil nitrogen, carbon, and phosphorus were measured. Degree of flooding, measured as flood frequency and flood interval, had the strongest impact on ant density in flooded forest. Flooding caused a linear decrease in ant abundance, potentially due to a reduction of suitable nesting sites. However, its influence on species richness varied: low-disturbance habitat had species richness equal to terra firme forest after adjusting for differences in density. The composition of ant genera and species varied among flood categories; some groups known to contain specialist predators were particularly intolerant to flooding. Hypoponera STD10 appeared to be well-adapted to highly flooded habitat. Although flooding did not appear to increase species richness or abundance at the habitat scale, low-flooding habitat contained a mixture of species found in the significantly distinct ant communities of terra firme and highly flooded habitat. [ABSTRACT FROM AUTHOR]

The positive role of moderate natural disturbance is less known for a mobile organism such as birds, compared to sessile organisms. In the face of recent declines of grassland birds, it is necessary to identify the mechanism to maintain avian diversity in early successional open habitats in different regions. In the humid temperate region, the predominant habitat type is woody vegetation. Therefore, bird communities were studied along vegetational succession using a chronosequence method. TWINSPAN identified three distinctive habitat types (barren, grass-fen and shrubland) and four habitat guilds of birds (pioneer, grassland, ubiquitous and shrub) in the study sites. Path analysis determined the direct and indirect effects of disturbance on the habitat guilds of birds. Short and intermediate intervals of the water disturbance are important to pioneer guilds and grass-fen habitat, respectively. The frequent occurrence of large animals had a negative impact on grassland guild. It suggests that grassland birds less tolerate cattle grazing or human activities in a region with intensive land use. The chronosequence study revealed the dynamic nature of the bird community. Birds occupy habitats following the successional sere of vegetation, responding to animal occurrence and human activities in various manners. [ABSTRACT FROM AUTHOR]

Communities exposed to intermediate disturbances have been shown to be more diverse than more stable or unstable systems. We recorded the diversity pattern of zooplankton in the Okavango Delta, Botswana, a system which include water bodies with different stability with regard to water levels and wet-dry phases, from permanent rivers and lagoons to seasonal floodplains and temporary water-filled rain ponds. The yearly flood pulse caused a gradual shift in aquatic parameters on seasonal floodplains, which promoted zooplankton diversity. Species composition differed between temporal and permanent habitats, but highest diversity was recorded on floodplains. Diversity on floodplains showed a distinct seasonal trend, being low during increasing flood, to highly diverse during high water periods. Density and hatching sequence of major eladoceran species suggested that the bank of resting eggs in the soil is the major source of species occurrence during flooding. We propose that seasonal floodplains, which have significant higher diversity and abundance, serve as source areas for the cladoceran diversity in the Okavango Delta. From these habitats ephippia are dispersed into the other four habitats. The dominant vectors for such dispersal are probably wind and mammals. [ABSTRACT FROM AUTHOR]

Patch dynamics, tree injury and mortality, and coarse woody detritus were quantified to examine the ecological impacts of Hurricane Fran on an oak-hickory-pine forest near Chapel Hill, NC. Data from long-term vegetation plots (1990–1997) and aerial photographs (1998) indicated that this 1996 storm caused patchy disturbance of intermediate severity (10–50% tree mortality; Woods, J Ecol 92:464–476, 2004). The area in large disturbance patches (>0.1 ha) increased from <1% to approximately 4% of the forested landscape. Of the forty-two 0.1-ha plots that were studied, 23 were damaged by the storm and lost 1–66% of their original live basal area. Although the remaining 19 plots gained basal area (1–15% increase), across all 42 stands basal area decreased by 17% because of storm impacts. Overall mortality of trees >10 cm dbh was 18%. The basal area of standing dead trees after the storm was 0.9 m2/ha, which was not substantially different from the original value of 0.7 m2/ha. In contrast, the volume and mass of fallen dead trees after the storm (129 m3/ha; 55 Mg/ha) were 6.1 and 7.9 times greater than the original levels (21 m3/ha; 7 Mg/ha), respectively. Uprooting was the most frequent type of damage, and it increased with tree size. However, two other forms of injury, severe canopy breakage and toppling by other trees, decreased with increasing tree size. Two dominant oak species of intermediate shade-tolerance suffered the largest losses in basal area (30–41% lost). Before the storm they comprised almost half of the total basal area in a forest of 13% shade-tolerant, 69% intermediate, and 18% shade-intolerant trees. Recovery is expected to differ with respect to vegetation (e.g., species composition and diversity) and ecosystem properties (e.g., biomass, detritus mass, and carbon balance). Vegetation may not revert to its former composition; however, reversion of biomass, detritus mass... [ABSTRACT FROM AUTHOR]

Anthropogenic land transformation is a consequence of human population growth and the associated agricultural, residential, and industrial needs. This study aimed to investigate the effects of anthropogenic activity and human-mediated land transformation on capture/recapture frequencies, species richness, and diversity of native small mammal community assemblages in the Magaliesberg Biosphere, North West province, South Africa. Five anthropogenically transformed land-use types were investigated: an animal rehabilitation and ecotourism center, an agricultural farmstead, a residential farmstead, a mine-adjacent agricultural farmstead, and a protected nature conservancy. We used live traps to sample small mammals during the dry and wet seasons over three consecutive years and compared population numbers and species composition across study sites and seasons. Capture/recapture frequencies differed significantly between sites and seasons, with the highest capture frequencies recorded at the agricultural and residential farmsteads. Species richness and diversity were highest at the residential and mine-adjacent farmsteads, both of which experienced intermediate levels of anthropogenic disturbance throughout the sampling period. The study shows that while natural and protected landscapes with low levels of disturbance are preferred, transformed landscapes can also be managed effectively to benefit native small mammal populations by regulating the frequency and intensity of human-mediated activities. [ABSTRACT FROM AUTHOR]

Dispersal ability is a factor of prime importance to explain biotic distributions. Yet, it is extremely difficult to measure directly. In this study, we take advantage of the natural experimental design of slag heap colonization in Belgium to document the timing and range of dispersal of bryophytes at the landscape scale. On the basis of a species atlas with a 4 × 4 km grid, the minimum distance separating species found on 52 slag heaps from potential source populations was determined. Minimum dispersal rates were inferred by coupling the information on minimum distance between slag heap and source populations with time since colonization. The number of species per slag heap is significantly correlated with time since colonization and area size. The frequency distribution of the longest dispersal events is highly skewed, with 44% of the species recruited within the nearest 6 km. In the remaining 56% of the species, recruitments from source populations located within a range of at least 6–86 km occurred within a period of less than 50 years. The majority of the species that are not recruited within the nearest vicinity of the slag heaps, including rare species at the regional scale, occur on slag heaps that have been colonized for 25–50 years. Most recently colonized slag heaps are indeed characterized by ‘fugitive’, weedy species, whereas slag heaps that have been colonized for > 50 years tend to accumulate perennial species with a ‘stayer’ life strategy. These observations suggest that rare species may display the dispersal ability to travel across the landscape, but are subsequently limited by their ability to establish a viable community because of more competitive neighbours. Rare species therefore tend to accumulate at intermediate colonization stages, which represent a trade-off between an increasing probability of colonization with time and a decreasing probability of establishment due to competition. [ABSTRACT FROM AUTHOR]