Showing papers in "Ecological Monographs in 2011"

The value of estuarine and coastal ecosystem services

Abstract: The global decline in estuarine and coastal ecosystems (ECEs) is affecting a number of critical benefits, or ecosystem services. We review the main ecological services across a variety of ECEs, including marshes, mangroves, nearshore coral reefs, seagrass beds, and sand beaches and dunes. Where possible, we indicate estimates of the key economic values arising from these services, and discuss how the natural variability of ECEs impacts their benefits, the synergistic relationships of ECEs across seascapes, and management implications. Although reliable valuation estimates are beginning to emerge for the key services of some ECEs, such as coral reefs, salt marshes, and mangroves, many of the important benefits of seagrass beds and sand dunes and beaches have not been assessed properly. Even for coral reefs, marshes, and mangroves, important ecological services have yet to be valued reliably, such as cross-ecosystem nutrient transfer (coral reefs), erosion control (marshes), and pollution control (mangroves). An important issue for valuing certain ECE services, such as coastal protection and habitat-fishery linkages, is that the ecological functions underlying these services vary spatially and temporally. Allowing for the connectivity between ECE habitats also may have important implications for assessing the ecological functions underlying key ecosystems services, such coastal protection, control of erosion, and habitat-fishery linkages. Finally, we conclude by suggesting an action plan for protecting and/or enhancing the immediate and longer-term values of ECE services. Because the connectivity of ECEs across land-sea gradients also influences the provision of certain ecosystem services, management of the entire seascape will be necessary to preserve such synergistic effects. Other key elements of an action plan include further ecological and economic collaborative research on valuing ECE services, improving institutional and legal frameworks for management, controlling and regulating destructive economic activities, and developing ecological restoration options.

Do mountain pine beetle outbreaks change the probability of active crown fire in lodgepole pine forests

Abstract: Disturbance interactions have received growing interest in ecological research in the last decade. Fire and bark beetle outbreaks have recently increased in severity and extent across western North America, raising concerns about their possible interactions. Although it is often presumed that bark beetle outbreaks increase probability of active crown fire by producing high loads of surface and canopy dead fuels, empirical data are scarce and results are ambivalent. We combined field measurements and modeling to address the following question: How do fuel characteristics, microclimate, and potential fire behavior change with time since a severe mountain pine beetle outbreak in Pinus contorta forests of Greater Yellowstone (Wyoming, USA)? We measured surface and canopy fuels, and soil surface temperature in a time-since-beetle-outbreak chronosequence (n = 35 sites) from undisturbed to 36 years post-outbreak, including stands in red- and gray-needle stages (respectively, 1–2 and 3–5 years post-outbreak). Fie...

An examination of synchrony between insect emergence and flowering in Rocky Mountain meadows

Abstract: One possible effect of climate change is the generation of a mismatch in the seasonal timing of interacting organisms, owing to species-specific shifts in phenology. Despite concerns that plants and pollinators might be at risk of such decoupling, there have been few attempts to test this hypothesis using detailed phenological data on insect emergence and flowering at the same localities. In particular, there are few data sets on pollinator flight seasons that are independent of flowering phenology, because pollinators are typically collected at flowers. To address this problem, we established standardized nesting habitat (trap nests) for solitary bees and wasps at sites along an elevational gradient in the Rocky Mountains, and monitored emergence during three growing seasons. We also recorded air temperatures and flowering phenology at each site. Using a reciprocal transplant experiment with nesting bees, we confirmed that local environmental conditions are the primary determinants of emergence phenology...

Pathogen impacts on plant communities: unifying theory, concepts, and empirical work

Abstract: Pathogens, like other consumers, mediate the outcome of competitive interactions between their host species. Ongoing efforts to integrate pathogens into plant community ecology could be accelerated by greater conceptual unification. Research on plant pathogens has mainly focused on a variety of disparate mechanisms—the Janzen-Connell hypothesis, plant–soil feedbacks, competition–defense trade-offs, escape of invasive plants from their enemies, and epidemic-driven community shifts—with limited recognition of how these mechanisms fit into the broader context of plant coexistence. Here, I extend an emerging theoretical framework for understanding species coexistence to include various pathogen impacts on plant communities. Pathogens can promote coexistence by regulating relative abundance or by reducing the disparities between species in fitness that make coexistence more difficult. Conversely, pathogens may undermine coexistence by creating positive feedbacks or by increasing between-species fitness differe...

Community assembly during secondary forest succession in a Chinese subtropical forest

Abstract: Subtropical broad-leaved forests in southeastern China support a high diversity of woody plants. Using a comparative study design with 30 × 30 m plots (n = 27) from five successional stages ( 1 m in height in each plot and counted all woody recruits (bank of all seedlings ≤1 m in height) in each central 10 × 10 m quadrant of each plot. In addition, we measured a number of environmen...

Generalized linear mixed models for phylogenetic analyses of community structure

Abstract: There is growing appreciation that ecological communities are phylogenetically structured, with phylogenetically closely related species either more or less likely to co-occur at the same site. Here, we present phylogenetic generalized linear mixed models (PGLMMs) that can statistically test a wide variety of phylogenetic patterns in community structure. In contrast to most current statistical approaches that rely on community metrics and randomization tests, PGLMMs are model-based statistics that fit observed presence/absence data to underlying hypotheses about the distributions of species among communities. We built four PGLMMs to address (1) phylogenetic patterns in community composition, (2) phylogenetic variation in species sensitivities to environmental gradients among communities, (3) phylogenetic repulsion in which closely related species are less likely to co-occur, and (4) trait-based variation in species sensitivities to environmental gradients. We also built a fifth PGLMM to test a key underlying assumption of phylogenetic community structure: that phylogenetic information serves as a surrogate for trait information about species; this model tests whether the introduction of trait information can explain all variation in species occurrences among communities, leaving no phylogenetic residual variation. We assessed the performance of these PGLMMs using community simulation models and show that PGLMMs have equal or greater statistical power than alternative approaches currently in the literature. Finally, we illustrate the PGLMM advantage of fitting a model to data by showing how variation in species occurrences among communities can be partitioned into phylogenetic and site-specific components, and how fitted models can be used to predict the co-occurrence of phylogenetically related species.

Toward a quantitative nutritional ecology: the right‐angled mixture triangle

Abstract: A recent area of progress in nutritional ecology is a growing awareness that nutritional phenotypes are best understood in a multidimensional context, where foraging is viewed as a process of balancing the intake and use of multiple nutrients to satisfy complex and dynamic nutrient needs. Numerous laboratory studies have shown that this view can yield novel insights into unresolved questions and provide a framework for generating new hypotheses. By contrast, progress with this multidimensional view has been slow in the arena of ultimate interest to functional biologists, the field. One reason for this is that the Geometric Framework for nutrition that has been extensively used in laboratory experiments focuses on amounts of nutrients (e.g., required, eaten, or retained), and such data are typically very difficult or impossible to collect for most free-ranging animals. Further, many problems in field-based nutritional ecology involve comparisons of mixtures that are expressed as proportions (e.g., food, diet, body, or fecal compositions), rather than absolute amounts. As yet, however, no geometric framework has been established in nutritional ecology for this. Here I recommend an approach for the geometric analysis of nutritional mixtures, and illustrate its use in a variety of contexts by reanalyzing published data. Despite its simplicity, this approach holds considerable promise for furthering the study of field-based nutritional ecology.

Modeling plant ranges over 75 years of climate change in California, USA: temporal transferability and species traits

Abstract: Species distribution model (SDM) projections under future climate scenarios are increasingly being used to inform resource management and conservation strategies. A critical assumption for projecting climate change responses is that SDMs are transferable through time, an assumption that is largely untested because investigators often lack temporally independent data for assessing transferability. Further, understanding how the ecology of species influences temporal transferability is critical yet almost wholly lacking. This raises two questions. (1) Are SDM projections transferable in time? (2) Does temporal transferability relate to species ecological traits? To address these questions we developed SDMs for 133 vascular plant species using data from the mountain ranges of California (USA) from two time periods: the 1930s and the present day. We forecast historical models over 75 years of measured climate change and assessed their projections against current distributions. Similarly, we hindcast contemporary models and compared their projections to historical data. We quantified transferability and related it to species ecological traits including physiognomy, endemism, dispersal capacity, fire adaptation, and commonness. We found that non-endemic species with greater dispersal capacity, intermediate levels of prevalence, and little fire adaptation had higher transferability than endemic species with limited dispersal capacity that rely on fire for reproduction. We demonstrate that variability in model performance was driven principally by differences among species as compared to model algorithms or time period of model calibration. Further, our results suggest that the traits correlated with prediction accuracy in a single time period may not be related to transferability between time periods. Our findings provide a priori guidance for the suitability of SDM as an approach for forecasting climate change responses for certain taxa.

Decomposition of the finest root branching orders: Linking belowground dynamics to fine-root function and structure

Abstract: Root turnover is fastest in the finest roots of the root system (first root order). Additionally, tissue chemistry varies among even the finest root orders and between white roots and older, pigmented roots. Yet the effects of pigmentation and order on root decomposition have rarely been examined. We separated the first four root orders (all <1 mm) of four temperate tree species into three classes: white first- and second-order roots; pigmented first- and second-order roots; and pigmented third- and fourth-order roots. Roots were enclosed in litterbags and buried under their own and under a common species canopy in a 34-year-old common garden in Poland. When comparing decomposition of different root orders over 36 months, pigmented third- and fourth-order roots with a higher C:N ratio decomposed more rapidly, losing 20–40% of their mass, than pigmented first- and second-order roots, which lost no more than 20%. When comparing decomposition of roots of different levels of pigmentation within the same root ...

Regulation of animal size by eNPP, Bergmann's rule, and related phenomena

Abstract: Bergmann's rule, which proposes a heat-balance explanation for the observed latitudinal gradient of increasing animal body size with increasing latitude, has dominated the study of geographic patterns in animal size since it was first proposed in 1847. Several critical reviews have determined that as many as half of the species examined do not fit the predictions of Bergmann's rule. We have proposed an alternative hypothesis for geographic variation in body size based on food availability, as regulated by the net primary production (NPP) of plants, specifically NPP during the growing season, or eNPP (ecologically and evolutionarily relevant NPP). Our hypothesis, “the eNPP rule,” is independent of latitude and predicts both spatial and temporal variation in body size, as well as in total population biomass, population growth rates, individual health, and life history traits of animals, including humans, wherever eNPP varies across appropriate scales of space or time. In the context of a revised interpretat...

Stability, resilience, and phase shifts in rocky subtidal communities along the west coast of Vancouver Island, Canada

Abstract: We used the extirpation, reintroduction, and spread of sea otters (Enhydra lutris) along the west coast of Vancouver Island, Canada, to evaluate how the otter–urchin–algae trophic cascade creates variation in rocky reef community structure over space and time By repeatedly sampling both randomly selected and permanently marked sites in areas where sea otters were continuously present, continuously absent, or became reestablished during a 23-year study period, we found a highly predictable association between community phase states (algae abundant or urchins abundant) and the population status of sea otters In areas where sea otters were continuously present, urchins were rare and algae dominated, whereas in areas where otters were continuously absent, urchins were abundant and algae were rare Despite this predictability, the species composition and abundance of algae within otter-dominated sites and the abundance of urchins in otter-free sites were spatially and temporally variable The transition from

The underpinnings of the relationship of species richness with space and time

Abstract: Various ecological mechanisms influence the forms of species richness relationships (SRRs). These mechanisms can be gathered under five general categories: more individuals, environmental heterogeneity, dispersal limitations, biotic interactions, and multiple species pools. Often only the first two categories are discussed. In contrast, we examine all five and explore how they can influence the form of SRRs. We discuss how various sampling schemes and methods of SRR construction can be used to gain insight about how various processes influence species richness patterns. The field is ripe for probing these effects through more complex simulation models or more sophisticated mathematical approaches. To facilitate deeper understanding, we need to embrace the full spectrum of SRRs and reconsider the assumed common knowledge about the functional form of SRRs. The relationship between species richness and the space or time over which it is sampled has received increasing attention over the past decade, resultin...

Habitat preference, accessibility, and competition limit the global distribution of breeding Black-browed Albatrosses

Abstract: Telemetry methods and remote sensing now make it possible to record the spatial usage of wide-ranging marine animals and the biophysical characteristics of their pelagic habitats. Furthermore, recent statistical advances mean that such data can be used to test ecological hypotheses and estimate species' distributions. Black-browed Albatrosses Thalassarche melanophrys are highly mobile marine predators with a circumpolar breeding and foraging distribution in the Southern Hemisphere. Although they remain relatively abundant, increased fisheries bycatch has led to their listing as endangered by conservation bodies. We satellite-tracked 163 breeding Black-browed Albatrosses and eight closely related Campbell Albatrosses T. impavida from nine colonies. We then quantified habitat usage, and modeled population-level spatial distribution at spatiotemporal scales >50 km and 1 month, as a function of habitat accessibility, habitat preference, and intraspecific competition, using mixed-effects generalized additive models (GAMM). During incubation, birds foraged over a wider area than in the post-brood chick-rearing period, when they are more time constrained. Throughout breeding, the order of habitat preference of Black-browed Albatrosses was for neritic (0-500 m), shelf-break and upper shelf-slope (500 1000 m), and then oceanic (>1000 m) waters. Black-browed Albatrosses also preferred areas with steeper (>3 degrees) bathymetric relief and, in addition, during incubation, warmer sea surface temperatures (peak preference similar to 16 degrees C). Although this suggests specialization in neritic habitats, incubation-stage Black-browed Albatrosses from South Georgia also foraged extensively in oceanic waters, preferring areas with high eddy kinetic energy (>250 cm(2)/s(2)), especially the Brazil-Malvinas Confluence, a region of intense mesoscale turbulence. During chick-rearing, this species had a more southerly distribution, and following the seasonal retreat of sea ice, birds from some populations utilized neritic polar waters. Campbell Albatrosses showed similar bathymetric preferences but also preferred positive sea level anomalies. Black-browed Albatross foraging areas were partially spatially segregated with respect to colony and region, with birds preferring locations distant from neighboring colonies, presumably in order to reduce competition between parapatric conspecifics. At the global scale, the greatest concentrations of breeding Black-browed Albatrosses are in southern South American neritic, shelf-break, and shelf-slope waters. These regions also hold large fisheries and should therefore be a priority for introduction of bycatch mitigation measures.

Causes and implications of the correlation between forest productivity and tree mortality rates

Abstract: At global and regional scales, tree mortality rates are positively correlated with forest net primary productivity (NPP). Yet causes of the correlation are unknown, in spite of potentially profound implications for our understanding of environmental controls of forest structure and dynamics and, more generally, our understanding of broad-scale environmental controls of population dynamics and ecosystem processes. Here we seek to shed light on the causes of geographic patterns in tree mortality rates, and we consider some implications of the positive correlation between mortality rates and NPP. To reach these ends, we present seven hypotheses potentially explaining the correlation, develop an approach to help distinguish among the hypotheses, and apply the approach in a case study comparing a tropical and temperate forest. Based on our case study and literature synthesis, we conclude that no single mechanism controls geographic patterns of tree mortality rates. At least four different mechanisms may be at play, with the dominant mechanisms depending on whether the underlying productivity gradients are caused by climate or soil fertility. Two of the mechanisms are consequences of environmental selection for certain combinations of life-history traits, reflecting trade-offs between growth and defense (along edaphic productivity gradients) and between reproduction and persistence (as manifested in the adult tree stature continuum along climatic and edaphic gradients). The remaining two mechanisms are consequences of environmental influences on the nature and strength of ecological interactions: competition (along edaphic gradients) and pressure from plant enemies (along climatic gradients). For only one of these four mechanisms, competition, can high mortality rates be considered to be a relatively direct consequence of high NPP. The remaining mechanisms force us to adopt a different view of causality, in which tree growth rates and probability of mortality can vary with at least a degree of independence along productivity gradients. In many cases, rather than being a direct cause of high mortality rates, NPP may remain high in spite of high mortality rates. The independent influence of plant enemies and other factors helps explain why forest biomass can show little correlation, or even negative correlation, with forest NPP.

A brown-world cascade in the dung decomposer food web of an alpine meadow: effects of predator interactions and warming

Abstract: Top-down control has been extensively documented in food webs based on living plants, where predator limitation of herbivores can cascade to facilitate plant growth (the green-world hypothesis), particularly in grasslands and aquatic systems. Yet the ecosystem role of predators in detrital food webs is less explored, as is the potential effect of climate warming on detritus-based communities. We here show that predators have a "brown-world" role in decomposer communities via a cascading top-down control on plant growth, based on the results of an experiment that factorially manipulated presence and size of two predator species as well as temperature (warmed vs. unwarmed). The inclusion of predatory beetles significantly decreased abundance of coprophagous beetles and thus the rate of dung decomposition and productivity of plants growing surrounding the dung. Moreover, the magnitude of these decreases differed between predator species and, for dung loss, was temperature dependent. At ambient temperature, the larger predators tended to more strongly influence the dung loss rate than did the smaller predators; when both predators were present, the dung loss rate was higher relative to the treatments with the smaller predators but comparable to those with the larger ones, suggesting an antagonistic effect of predator interaction. However, warming substantially reduced dung decomposition rates and eliminated the effects of predation on dung decomposition. Although warming substantially decreased dung loss rates, warming only modestly reduced primary productivity. Consistent with these results, a second experiment exploring the influence of the two predator species and warming on dung loss over time revealed that predatory beetles significantly decreased the abundance of coprophagous beetles, which was positively correlated with dung loss rates. Moreover, experimental warming decreased the water content of dung and hence the survival of coprophagous beetles. These results confirm that the "brown-world" effect of predator beetles was due to cascading top-down control through coprophagous beetles to nutrient cycling and primary productivity. Our results also highlight potentially counterintuitive effects of climate warming. For example, global warming might significantly decrease animal-mediated decomposition of organic matter and recycling of nutrients in a future warmed world.

The spatial scale of plant-animal interactions: effects of resource availability and habitat structure

Abstract: Plant–animal interactions are crucial nodes in the structure of communities and pivotal drivers of ecosystem functioning. Much of this relevance may depend on how animals cope with plant resources at different spatial scales. However, little is known about how and why different interactions perform at different scales in the same environmental setting. In this study we assess the spatial scales at which two plant–animal interactions operate and disentangle the environmental factors (plant resource availability vs. habitat structure) underpinning these operational scales. We studied two interactions with opposite (mutualistic vs. antagonistic) ecological effects on fleshy-fruited trees, frugivory and seed dispersal by birds, and the later predation by rodents on bird-dispersed seeds. Employing a standardized sampling, we covered three temperate ecosystems hosting structurally similar plant–frugivore–seed predator systems: Cantabrian forest, Mediterranean shrubland, and Patagonian forest. We sampled habitat...

Successful invaders co-opt pollinators of native flora and accumulate insect pollinators with increasing residence time.

Abstract: Pollination mode is an important reproductive characteristic, often assumed to play a considerable role in plant species invasiveness We asked (1) whether alien and native species differed in the frequency of pollination modes (insect pollination, self-pollination, wind pollination, water pollination), (2) whether the pollination modes affected the invasion success of two groups of aliens, differing in their residence time in Central Europe: archaeophytes (introduced before 1500) and neophytes (introduced more recently), and (3) whether there were differences in the diversity of insect pollinators of native species, and of alien species at different stages of invasion and with different residence time The analysis was carried out using 2817 species occurring in the Czech Republic (1596 native and 1221 alien, the latter comprising 331 archaeophytes and 890 neophytes) Data were analyzed using generalized linear models The alien flora introduced to Central Europe contained a higher proportion of insect-pollinated species than did the Central European native flora and linked to a higher diversity of pollinators per species However, the frequency of pollination modes in the introduced alien flora gradually changed during the process of naturalization, becoming more similar to that of native species, and eventually, the naturalized species that became invasive did not differ in their frequency of pollination modes from native species The frequency of self-pollination increased from casual through naturalized to invasive alien species This suggests a remarkable role for pollination mode in successful invasions; indeed, self-pollination tends to support spread of neophytes more than any other mode of pollination The range of habitats occupied by plants of different invasion status affected the diversity of insect pollinator species In contrast, regional commonness of plant species only affected the number of pollinator functional groups In native species and archaeophytes, there was a steeper accumulation of pollinator species with increasing habitat range than in neophytes This indicates that groups of plants that have been provided with longer time to sample a wider range of habitats than recently arriving alien species have formed more associations with native pollinator species occurring in those habitats

Ecological effects on metabolic scaling: amphipod responses to fish predators in freshwater springs

Abstract: Metabolic rate is commonly thought to scale with body mass to the 3/4 power as a result of universal body design constraints. However, recent comparative work has shown that the metabolic-scaling slope may vary significantly among species and higher taxa, apparently in response to different lifestyles and ecological conditions, though the precise mechanisms involved are not well understood. To better understand these underappreciated ecological effects and their causes, it is important to control for extraneous phylogenetic and environmental influences. We demonstrate how this may be done by comparing the ontogenetic scaling of resting metabolic rate among populations of the same species (the amphipod Gammarus minus) in mid-Appalachian freshwater springs with similar, relatively constant environmental conditions, except for the varying presence of the predatory fish Cottus cognatus. We found that populations of G. minus exhibit significantly lower metabolic-scaling slopes (0.54–0.62) in three freshwater s...

Decomposing environmental, spatial, and spatiotemporal components of species distributions

Abstract: Species distribution models are an important tool to predict the impact of global change on species distributional ranges and community assemblages. Although considerable progress has been made in the statistical modeling during the last decade, many approaches still ignore important features of species distributions, such as nonlinearity and interactions between predictors, spatial autocorrelation, and nonstationarity, or at most incorporate only some of these features. Ecologists, however, require a modeling framework that simultaneously addresses all these features flexibly and consistently. Here we describe such an approach that allows the estimation of the global effects of environmental variables in addition to local components dealing with spatiotemporal autocorrelation as well as nonstationary effects. The local components can be used to infer unknown spatiotemporal processes; the global component describes how the species is influenced by the environment and can be used for predictions, allowing ...

Impacts of aspergillosis on sea fan coral demography: modeling a moving target

Abstract: Little is known about how epizootics in natural populations affect vital rates and population structure, or about the process of recovery after an outbreak subsides. We investigated the effects of aspergillosis, an infectious disease caused by the fungal pathogen Aspergillus sydowii, on the demography of a gorgonian coral, Gorgonia ventalina. Caribbean sea fans were affected by a seven-year epizootic, marked by an initial period in 1994 of high infection prevalence, high mortality rates, and almost complete reproductive failure of infected fans. Post epizootic, in 2005, host populations were relatively healthy, with low disease prevalence. Using longitudinal data from populations on coral reefs in the Florida Keys (USA) and the Yucatan Peninsula (Mexico), we documented changes in the epidemiology of sea fan aspergillosis over the course of the epizootic. We developed an ''integral projection model'' that scales disease impacts from individual to population levels using direct estimates of vital rates. Within-colony lesion growth rate and host mortality were higher during the peak of the epizootic. Effects on individuals and populations changed substantially post-epizootic; recruitment increased, mortality of infected adults decreased, and the size dependence of infection was reduced. Elasticity analysis indicated that population growth is more sensitive to changes in the growth and survival of established colonies than to recruitment, due to slow colony growth and the longevity and fecundity of large adults. Disease prevalence in our monitored populations decreased from ;50% in 1997 to ,10% by 2003 and ,1% in 2007 and was accompanied by very high mortality during the early stages of the epizootic. The population model suggested that host evolution (due to selection for higher disease resistance through differential mortality) could proceed quickly enough to explain the observed changes in prevalence and in the size independence of infection risk. Our model indicates that the time required for population recovery following an outbreak is largely determined by the percentage of healthy tissue lost from the population. However, recovery following an especially severe outbreak (i.e., 80% or more tissue loss) is much faster if the affected population receives an external supply of recruits from unaffected areas.

Broadscale variability in tree data of the historical Public Land Survey and its consequences for ecological studies

Abstract: Historical records provide valuable information on the prior conditions of ecological systems and species distribution, especially in the context of growing environmental change. However, historical records may have associated bias and error because their original purpose may not have been for scientific use. The Public Land Survey (PLS) of the U.S. General Land Office (GLO) conducted from the late 1700s to the early 1900s has been widely used to characterize historical vegetation in the United States prior to major Euro-American settlements. Studies have shown that variability and bias exist in the data. However, these studies have not typically encompassed a region large enough to adequately assess this variability across diverse landscapes, nor attempted to distinguish potential ecological significance from statistical differences. Here we do this by analyzing variability in PLS data across all of northern Wisconsin, USA, a 75 000-km 2 landscape. We found ecologically significant differences among survey point types for tree species, size, and the distance to survey points. Both corner and line trees show some level of bias for species and size, but corner trees are likely the best sample. Although statistical tests show significant differences in species composition, tree size, and distance by tree sequence and location, the differences in species composition and tree size are not ecologically significant. The species differences are probably caused by fine-scale variability in the forest communities. The value of the PLS data remains high; choice of spatial extent, methods of analyses, and bias significance need to be evaluated according to variables of interest and project purpose.

Hawaiian ant–flower networks: nectar-thieving ants prefer undefended native over introduced plants with floral defenses

Abstract: Ants are omnipresent in most terrestrial ecosystems, and plants have responded to their dominance by evolving traits that either facilitate positive interactions with ants or reduce negative ones. Because ants are generally poor pollinators, plants often protect their floral nectar against ants. Ants were historically absent from the geographically isolated Hawaiian archipelago, which harbors one of the most endemic floras in the world. We hypothesized that native Hawaiian plants lack floral features that exclude ants and therefore would be heavily exploited by introduced, invasive ants. To test this hypothesis, ant–flower interactions involving co-occurring native and introduced plants were observed in 10 sites on three Hawaiian Islands. We quantified the residual interaction strength of each pair of ant–plant species as the deviation of the observed interaction frequency from a null-model prediction based on available nectar sugar in a local plant community and local ant activity at sugar baits. As pred...

Cross-sectional vs. longitudinal research: a case study of trees with hollows and marsupials in Australian forests

Abstract: How different are insights based on cross-sectional studies from those of longitudinal investigations? We addressed this question using a detailed case study encompassing a rare suite of inter-connected cross-sectional and longitudinal investigations that have spanned the past two decades and included work on: (1) the decay and collapse of large-cavity forest trees (termed “trees with hollows”), (2) populations of a suite of species of arboreal marsupials that are reliant on trees with hollows as nesting and denning sites, and (3) relationships between the abundance, type, and condition of trees with hollows and the presence, abundance, and species richness of these animals. Our case study was from the montane ash eucalypt forests of the Central Highlands of Victoria, southeastern Australia. Our longitudinal studies led to new insights that either would not have been possible from a cross-sectional study, or which were unexpected because they did not conform, or only partially conformed, to postulated res...

Bayesian state‐space modeling of metapopulation dynamics in the Glanville fritillary butterfly

Abstract: The complexity of mathematical models of ecological dynamics varies greatly, and it is often difficult to judge what would be the optimal level of complexity in a particular case. Here we compare the parameter estimates, model fits, and predictive abilities of two models of metapopulation dynamics: a detailed individual-based model (IBM) and a population-based stochastic patch occupancy model (SPOM) derived from the IBM. The two models were fitted to a 17-year time series of data for the Glanville fritillary butterfly (Melitaea cinxia) inhabiting a network of 72 small meadows. The data consisted of biannual counts of larval groups (IBM) and the annual presence or absence of local populations (SPOM). The models were fitted using a Bayesian state-space approach with a hierarchical random effect structure to account for observational, demographic, and environmental stochasticities. The detection probability of larval groups (IBM) and the probability of false zeros of local populations (SPOM) in the observati...

Testing the accuracy of new methods for reconstructing historical structure of forest landscapes using GLO survey data

Abstract: The accuracy of methods for reconstructing parameters (e.g., tree density) of historical forest structure from General Land Office (GLO) survey data has not been thoroughly assessed. Past simulation and statistical assessments of plotless density estimators have focused on minimizing estimation error, but not congruent with the specific data available in the GLO surveys. Most GLO reconstruction studies do not reconstruct absolute measures of density, basal area, or diameter-class distributions, key measures used for forest restoration. We tested the accuracy of a suite of plotless density estimators and other survey methods to accurately reconstruct forest attributes using both a field-based modern calibration and a cross-validation with tree-ring reconstructions. In addition to the common distance estimators, we developed several Voronoi-based plotless density estimators that can be used with GLO data. Estimators were assessed using modern survey and plot data collected in the same location and spatial arrangement as the original survey locations in three geographically distinct areas. Results showed that Voronoi-based density estimators were superior to distance-based estimators. Data need to be pooled across locations. Voronoi estimators yielded more accurate measures of density and basal area and can be used at smaller pooling levels without sacrificing much accuracy. At spatial extents of 260 and 520 ha (3- and 6-corner pools), relative mean absolute error (RMAE) averaged 29% and 22%, respectively, for density estimates in all three study areas. To estimate basal area as accurately (i.e., 23%), data must be pooled to 780 ha (9-corner pool). Composition and diameter-class distributions also required larger pooling areas to achieve accurate results. In the cross-validation, accuracy of density and basal area were both superior to accuracy in the modern calibration, and RMAE for density and basal area at all pooling levels averaged 16.6% and 15.7%, respectively. Composition and diameter-class distribution estimates were lower in accuracy. Voronoi-based methods can accurately estimate historical forest parameters across large landscapes and are accurate at finer scales (e.g., 260 ha, 3-corner pool) than previously thought possible. GLO reconstructions complement tree-ring reconstructions but can provide more spatially comprehensive estimates of the historical range of forest variability, facilitating landscape-level restoration.

Decomposition of heterogeneous organic matter and its long-term stabilization in soils

Abstract: Soil organic matter is a complex mixture of material with heterogeneous biological, physical, and chemical properties. Decomposition models represent this heterogeneity either as a set of discrete pools with different residence times or as a continuum of qualities. It is unclear though, whether these two different approaches yield comparable predictions of organic matter dynamics. Here, we compare predictions from these two different approaches and propose an intermediate approach to study organic matter decomposition based on concepts from continuous models implemented numerically. We found that the disagreement between discrete and continuous approaches can be considerable depending on the degree of nonlinearity of the model and simulation time. The two approaches can diverge substantially for predicting long-term processes in soils. Based on our alternative approach, which is a modification of the continuous quality theory, we explored the temporal patterns that emerge by treating substrate heterogenei...

Potential impact of climate‐related changes is buffered by differential responses to recruitment and interactions

Abstract: Detection of ecosystem responsiveness to climatic perturbations can provide insight into climate change consequences. Recent analyses linking phytoplankton abundance and mussel recruitment to the North Pacific Gyre Oscillation (NPGO) revealed a paradox. Despite large increases in mussel recruitment beginning in 2000, adult mussel responses were idiosyncratic by site and intertidal zone, with no response at one long-term site, and increases in the low zone (1.5% per year) and decreases in the mid zone (1.3% per year) at the other. What are the mechanisms underlying these differential changes? Species interactions such as facilitation by barnacles and predation are potential determinants of successful mussel colonization. To evaluate these effects, we analyzed patterns of barnacle recruitment, determined if predation rate covaried with the increase in mussel recruitment, and tested facilitation interactions in a field experiment. Neither magnitude nor season of barnacle recruitment changed meaningfully with...

Floodplain succession and soil nitrogen accumulation on a salmon river in southwestern Kamchatka

Abstract: We documented riparian primary succession on an expansive floodplain (Kol River, Kamchatka, Russian Federation) that receives large nitrogen subsidies from spawning Pacific salmon. As is typical of primary succession, new alluvial deposits in the lower Kol floodplain were nitrogen poor (200 kg persulfate N/ha to 10 cm soil depth); however, nitrogen accumulated rapidly, and soils contained 1600 kg N/ha (to 10 cm + the litter layer) by 20 years. Soil nitrogen approached an asymptote at ∼2500 kg N/ha by 80 years. Nitrogen-fixing Alnus trees were a minor component of the forest community during the first 20 years of succession. However, salmon carcasses were a substantial nitrogen source during this period of rapid nitrogen accumulation. Similar to other northern Pacific Rim floodplains, we found that new alluvial deposits were colonized by Salix, Chosenia, and Alnus trees; but, unlike other described chronosequences, the community transitioned into meadows of tall forbs (some >2.5 m in height) dominated by F...

Random-effects ordination: describing and predicting multivariate correlations and co-occurrences

Abstract: Ecology is inherently multivariate, but high-dimensional data are difficult to understand. Dimension reduction with ordination analysis helps with both data exploration and clarification of the meaning of inferences (e.g., randomization tests, variation partitioning) about a statistical population. Most such inferences are asymmetric, in that variables are classified as either response or explanatory (e.g., factors, predictors). But this asymmetric approach has limitations (e.g., abiotic variables may not entirely explain correlations between interacting species). We study symmetric population-level inferences by modeling correlations and co-occurrences, using these models for out-of-sample prediction. Such modeling requires a novel treatment of ordination axes as random effects, because fixed effects only allow within-sample predictions. We advocate an iterative methodology for random-effects ordination: (1) fit a set of candidate models differing in complexity (e.g., number of axes); (2) use information...

Seed fate and seedling dynamics after masting in two African rain forest trees

Abstract: How the effects of biotic factors are moderated by abiotic factors, and their consequences for species interactions, is generally understudied in ecology. A key abiotic feature of forests is regular canopy disturbances that create temporary patches, or “gaps,” of above-average light availability. Co-occurring in lowland primary forest of Korup National Park (Cameroon), Microberlinia bisulcata and Tetraberlinia bifoliolata are locally dominant, ectomycorrhizal trees whose seeds share predator guilds in masting years. Here, we experimentally tested the impact of small mammal predators upon seedling abundance, growth, and survivorship. In 2007, we added a fixed density of seeds of each species to exclosures at 48 gap–understory locations across 82.5 ha within a large Microberlinia grove, and at 15 locations outside it. For both species, small mammals removed more seeds in gaps than in understory, whereas this was reversed for seeds killed by invertebrates. Nonetheless, Microberlinia lost twice as many seeds to small mammals, and more to invertebrates in exclosures, than Tetraberlinia, which was more prone to a pathogenic white fungus. After six weeks, both species had greater seedling establishment in gaps than understory, and in exclosures outside compared to exclosures inside the grove. In the subsequent two-year period, seedling growth and survivorship peaked in exclosures in gaps, but Microberlinia had more seedlings' stems clipped by animals than Tetraberlinia, and more than twice the percentage of leaf area damaged. Whereas Microberlinia seedling performance in gaps was inferior to Tetraberlinia inside the grove, outside it Microberlinia had reduced leaf damage, grew taller, and had many more leaves than Tetraberlinia. No evidence was found for “apparent mutualism” in the understory as seedling establishment of both species increased away from (>25 m) large stems of either species, pointing to “apparent competition” instead. In gaps, Microberlinia seedling establishment was lower near Tetraberlinia than conspecific adults because of context-dependent small mammal satiation. Stage-matrix analysis suggested that protecting Microberlinia from small mammals could increase its population growth rate by 0.06. In the light of prior research we conclude that small mammals and canopy gaps play an important role in promoting species coexistence in this forest, and that their strong interaction contributes to Microberlinia's currently very poor regeneration.