Spatial Heterogeneity In Species Composition Research Articles

Improving restoration outcomes of boreal Sphagnum-dominated peatlands after peat-extraction: The key role of phosphorus fertilization

Fertilization is a common and effective restoration practice for some ecosystems. However, there are still knowledge gaps about the long-term effectiveness and impact of phosphorus fertilization during the restoration of degraded boreal Sphagnum peatlands using the Moss Layer Transfer Technique. Data gathered from 114 peatland sectors restored 1 to 25 years ago, encompassing around 2900 surveyed plots in Eastern Canada, were analyzed to investigate the influence of fertilization on plant re-establishment (cover, height, and aboveground biomass accumulation) and community composition. Fertilization with a low phosphorus dosage (1.64 g P m−2) of granular phosphate rock (P2O5; NPK 0–13-0) proved to accelerate peatland vegetation recovery by favoring a shift in plant community composition towards a Sphagnum dominance. This shift was encouraged by the fast colonization of Polytrichum strictum after fertilization, a nurse plant that stabilizes the peat substrate and facilitates the subsequent establishment of Sphagnum. Phosphorus fertilization increased by 42 % Sphagnum cover 25-year post-restoration and increased approximately by 15 % aboveground biomass accumulation 20-year post-restoration. Conversely, without fertilization, the success of restoration and long-term vegetation trajectories were uncertain. Phosphorus fertilization led to an increase in plant richness in the first 5 to 10 years after restoration and enhanced spatial heterogeneity in species composition throughout the later stages of restoration (20–25 years), suggesting that fertilization may foster dynamic, diverse plant communities. This study emphasizes fertilization's key role in restoring boreal Sphagnum peatland plant communities, especially in areas prone to episodes of freeze-thaw cycles, strongly advocating for the mandatory inclusion of phosphorus fertilization in the restoration process.

Alpha and beta diversity jointly drive the aboveground biomass in temperate and tropical forests.

Changes in biodiversity often affect ecosystem functioning. However, most previous biodiversity and ecosystem functioning (BEF) studies have generally been limited to very small spatial grains. Thus, knowledge regarding the biodiversity-ecosystem functioning relationships across spatial scales is lacking. Moreover, the multiscale nature of biodiversity, and specifically β diversity (i.e., spatial heterogeneity in species composition) was still largely missing in BEF studies. Here, using the vegetation and functional trait data collected from four 6-ha forest dynamics plots (FDPs) in temperate and tropical forests in China, we examine the scale-dependent relationships between tree diversity and the aboveground biomass (AGB), as well as the roles of species spatial heterogeneity in determining the AGB. In tropical forests, the effect of species richness on AGB decreased with spatial grains, while functional dominance played a stronger role at larger spatial grains. In temperate forests, positive relationship between diversity and AGB occurred at all spatial grains, especially on smaller scales. In both temperate and tropical forests, β diversity was positively correlated with AGB, but weaker than α diversity in determining AGB. Overall, complementarity and selection hypothesis play dominant role in determining AGB in temperate and tropical forests, respectively. The roles of these underlying mechanisms are more pronounced with increasing spatial scales. β diversity, a hitherto underexplored facet of biodiversity, is likely to increase ecosystem functions by species spatial turnover and should not be neglected in BEF explorations. Our findings have practical implications for forest management and demonstrate that biotic heterogeneity plays an important positive role in ecosystem functioning.

Plant\u2013plant interactions and local patterns of diversity from semi-arid to subalpine Mediterranean plant communities

An understanding of the diversity spatial organization in plant communities provides essential information for management and conservation planning. In this study we investigated, using a multi-species approach, how plant–plant interactions determine the local structure and composition of diversity in a set of Mediterranean plant communities, ranging from semi-arid to subalpine habitats. Specifically, we evaluated the spatial pattern of diversity (i.e., diversity aggregation or segregation) in the local neighborhood of perennial plant species using the ISAR (individual species–area relationship) method. We also assessed the local pattern of beta-diversity (i.e., the spatial heterogeneity in species composition among local assemblages), including the contribution of species turnover (i.e., species replacement) and nestedness (i.e., differences in species richness) to the overall local beta-diversity. Our results showed that local diversity segregation decreased in the less productive plant communities. Also, we found that graminoids largely acted as diversity segregators, while forbs showed more diverse neighborhoods than expected in less productive study sites. Interestingly, not all shrub and dwarf shrub species aggregated diversity in their surroundings. Finally, an increase in nestedness was associated with less segregated diversity patterns in the local neighborhood of shrub species, underlining their role in creating diversity islands in less productive environmental conditions. Our results provide further insights into the effect of plant–plant interactions in shaping the structure and composition of diversity in Mediterranean plant communities, and highlight the species and groups of species that management and conservation strategies should focus on in order to prevent a loss of biodiversity.

Spatial heterogeneity of soil fungal diversity in area with presence of Stellera chamaejasme on the degraded alpine meadow

Stellera chamaejasme is one of the most serious weeds in Qinhai-Tibetan Plateau, the rapid expansion of which exerts an increasing effect on the alpine meadow ecosystem. With high-throughput sequencing technology, geostatistics and GIS method, the spatial heterogeneity of soil fungal diversity in Stellera occurrence area and the spatial correlation between Stellera coverage and soil fungal diversity were investigated in a typical degraded alpine meadow of the Qilian Mountain. Compared to no-Stellera area, the fungi richness in Stellera area decreased, the dominance increased, and the α-diversity reduced. The difference of fungal species composition enhanced and β-diversity significantly increased. The spatial pattern of soil fungal diversity was affected by the invasion of Stellera, resulting in higher fragmentation in occurrence area. Spatial heterogeneity of species composition increased remarkably, and spatial stability of α-diversity and β-diversity decreased. The portion of positive correlation and negative correlation interlaced, indicating no clear spatial correlation between Stellera coverage and soil fungal diversity. Our results indicate that the spatial pattern of soil fungal diversity was affected by the interaction of soil and vegetation in Stellera invaded meadows.

Disturbances by the European ground squirrel enhance diversity and spatial heterogeneity of plant communities in temperate grassland

Fossorial rodents are recognized as diversity drivers in grassland ecosystems and are therefore considered ecosystem engineers and keystone species. However, there is a lack of evidence regarding this function for species in temperate grasslands, especially one of the most threatened, the European ground squirrel. We examined the effect of the European ground squirrel on plant species composition and diversity along the disturbance gradient mediated by their different population density and subsequently different disturbance intensity. We evaluated the effect of ground squirrel disturbance on plant diversity patterns in two plant communities with different species richness to determine whether the same pattern exists in contrasting habitats. In each plant community, we established transect of 25 × 250 m composed of 10 quadrats with different disturbance intensities of the ground squirrels. Vascular plant species were recorded in 320 plots of 1 m2. The distribution of individual species along the ground squirrel-mediated disturbance gradient was analysed using redundancy analysis. Diversity measures were calculated and modelled as a function of disturbances using generalized additive models. We observed significant compositional changes in plant communities accompanied by a reduction in dominant graminoid cover and a non-decreasing trend in forb cover along the disturbance gradient in both types of communities. We found that increasing disturbance activity leads to an increase in diversity at coarse spatial scale (625 m2) and spatial heterogeneity in species composition of both species-poor and species-rich plant community. The fine-scale (1 m2) diversity increased significantly only in species-poor community. Our results demonstrate that the European ground squirrel can be deservedly labelled as an important ecosystem engineer and keystone species promoting the diversity and heterogeneity of European temperate grasslands.

Spatial heterogeneity in species composition constrains plant community responses to herbivory and fertilisation.

Environmental change can result in substantial shifts in community composition. The associated immigration and extinction events are likely constrained by the spatial distribution of species. Still, studies on environmental change typically quantify biotic responses at single spatial (time series within a single plot) or temporal (spatial beta diversity at single time points) scales, ignoring their potential interdependence. Here, we use data from a global network of grassland experiments to determine how turnover responses to two major forms of environmental change - fertilisation and herbivore loss - are affected by species pool size and spatial compositional heterogeneity. Fertilisation led to higher rates of local extinction, whereas turnover in herbivore exclusion plots was driven by species replacement. Overall, sites with more spatially heterogeneous composition showed significantly higher rates of annual turnover, independent of species pool size and treatment. Taking into account spatial biodiversity aspects will therefore improve our understanding of consequences of global and anthropogenic change on community dynamics.

Urbanization promotes the loss of seasonal dynamics in the semi-natural grasslands of an East Asian megacity

The biodiversity of agricultural landscapes has been noticeably affected by rapid urbanization. Although many studies have examined species diversity per unit area (alpha diversity), knowledge about the patterns of species turnover (beta diversity) in urban areas remains limited. Furthermore, most beta diversity studies have focused on spatial heterogeneity; however, losses of temporal heterogeneity resulting from urbanization remain limited. In this study, we examined how urbanization is associated with decreases in the seasonal heterogeneity of species composition, which could be used as an indicator of the loss of seasonality by ecologists and policy makers aiming to conserve biodiversity. We investigated (1) changes in species richness based on seasonal averages (alpha diversity) and (2) the seasonal turnover of species composition (beta diversity) for flowering plants and butterflies along a rural-urban gradient in semi-natural grasslands. The response variables were alpha and beta diversity for flowering plants and butterflies, and the explanatory variables were urban areas within a 1-km radius of the center of each site. Increasing urban area caused both the seasonal alpha and beta diversity of flowering plants and butterflies to decline. These results supported the homogenization hypothesis for the seasonality of plants and butterflies in semi-natural grasslands of dominant urban areas in East Asia. Future studies should focus on investigating how urbanization is causing both declines in seasonality and changes in the spatial heterogeneity of species composition and associated biodiversity loss. Ecologists and policy makers should focus on developing strategies to halt the loss of temporal biological heterogeneity to maintain biodiversity.

Temporal heterogeneity increases with spatial heterogeneity in ecological communities.

Heterogeneity is increasingly recognized as a foundational characteristic of ecological systems. Under global change, understanding temporal community heterogeneity is necessary for predicting the stability of ecosystem functions and services. Indeed, spatial heterogeneity is commonly used in alternative stable state theory as a predictor of temporal heterogeneity and therefore an early indicator of regime shifts. To evaluate whether spatial heterogeneity in species composition is predictive of temporal heterogeneity in ecological communities, we analyzed 68 community data sets spanning freshwater and terrestrial systems where measures of species abundance were replicated over space and time. Of the 68 data sets, 55 (81%) had a weak to strongly positive relationship between spatial and temporal heterogeneity, while in the remaining communities the relationship was weak to strongly negative (19%). Based on a mixed model analysis, we found a significant but weak overall positive relationship between spatial and temporal heterogeneity across all data sets combined, and within aquatic and terrestrial data sets separately. In addition, lifespan and successional stage were negatively and positively related to temporal heterogeneity, respectively. We conclude that spatial heterogeneity may be a predictor of temporal heterogeneity in ecological communities, and that this relationship may be a general property of many terrestrial and aquatic communities.

Non‐interacting impacts of fertilization and habitat area on plant diversity via contrasting assembly mechanisms

AbstractAimThe local‐ and regional‐based forms of anthropogenic change reducing grassland diversity are generally identified, but these scale‐dependent processes tend to co‐occur with unclear interactive effects. Here, we explicitly test how common local and regional perturbations simultaneously affect plant alpha and beta diversity in a multiyear community assembly experiment using fragments of grassland habitat of various sizes. We hypothesized that local disturbances and decreasing patch size would interact, suppressing local diversity while homogenizing composition among patches.LocationNorth America.MethodsWe conducted a three‐year grassland assembly experiment, factorially manipulating local perturbation (nitrogen addition and mowing) and patch area for 36 patches over 13 ha. We quantified the individual and interactive effects of these local and regional factors on plant alpha and beta diversity within (quadrat scale) and among patches (patch scale). We also used a null model approach to disentangle between stochastic‐ and niche‐based assembly mechanisms.ResultsWe detected a gradient of assembly outcomes driven by two non‐interacting factors—the effects of N fertilization on alpha (negative) and beta (positive) diversity regardless of spatial scale and the scale‐dependant effect of increasing patch size on alpha (positive) and beta (positive) diversity. These effects unfolded over time, with the constraints on richness and composition shifting from dispersal‐based during the first sampling year to perturbation‐and size‐based factors at year two and three. Fertilization effects were driven by a mixture of deterministic (i.e., selection at the species level) and stochastic (i.e., random extinctions) processes resulting in a decline in local richness but an increase in spatial heterogeneity in species composition. Area appeared to influence alpha diversity mainly via stochastic “sampling effect”—larger patches represented a larger sample of the regional pool. Niche‐based processes, however, led to convergence in beta diversity among smaller patches driving a positive overall effect of area on beta diversity.Main conclusionOur results illustrate how diversity regulation in contemporary grasslands can be simultaneously shaped by local and regional factors acting additively but via contrasting assembly mechanisms that operate at different spatial and temporal scales.

Microbial pesticide application during defoliator outbreaks may reduce loss of regional forest beetle richness

To date, research on the effects of forest defoliator outbreaks and pesticide applications to suppress these outbreaks on non‐target forest arthropods has generally focused on non‐target Lepidoptera and has not examined effects on regional diversity. In this study, we assessed the effects of forest defoliation by gypsy moths and application of the microbial pesticide Bacillus thuringiensis var. kurstaki (Btk) to suppress gypsy moth populations on the species richness and (Shannon index) diversity of beetles in Shenandoah National Park, Virginia. In addition, we examined how these disturbances affected overall beetle abundance and abundances within different feeding guilds (herbivore, predator, fungivore, or xylophage). Three years after a gypsy moth outbreak, beetles were sampled four times throughout spring and summer at 15 sites belonging to one of three disturbance histories: undisturbed, defoliated, or sprayed with Btk. Beetles were captured using blacklight traps and then sorted to family and morphospecies. We did not detect significant effects of defoliation or Btk on local species richness (α richness) or local diversity (α diversity) of beetles. However, defoliated sites had lower β richness, i.e., lower heterogeneity in beetle species composition among sites, in early summer than sites that were undisturbed or sprayed with Btk. Overall beetle abundance was lower in spring at sites sprayed with Btk, but not significantly different among disturbance histories in other seasons. Further, effects of disturbance history on abundance were not significantly different among feeding guilds. Though the local (α) richness and diversity of beetles were not significantly influenced by gypsy moth defoliation or Btk, the reduced spatial heterogeneity of species composition (lower β richness) in defoliated areas suggests gypsy moth outbreaks could adversely affect regional species richness (γ richness). Our findings additionally suggest that Btk may protect against negative effects of gypsy moth defoliation on the regional species richness of beetles.

Conservation value of alternative land-use systems for dung beetles in Amazon: valuing traditional farming practices

Land-use systems (LUS), placed in originally forested areas, represent different degrees of opportunity for species conservation. In this study, we examined the dung beetle communities in order to identify the conservation value of different LUS: primary forest, old secondary forest, young secondary forest, agroforestry, agriculture and pasture in Western Amazon. The LUS were sampled in two campaigns during the highest precipitation period and dryest period. The primary forest has a high number of total and exclusive species. Large beetles show a continuous decreasing in richness and abundance from primary forest to pastures, while small ones are not sensible to intermediate systems (secondary forest to agriculture) in terms of species richness and exhibit a increase in abundance at agroforest and agriculture when contrasted to secondary forest and pasture The beetle community composition was not sensible to secondary forest recovering time. Secondary forests and agroforestry stood out as harboring many species shared with primary forests. Cloud-point dispersion (average dissimilarity) increased from primary forest towards LUS’s submitted to more intense use. The higher sampling points similarity observed in primary forest might be the result of the relative stability of this system, given that environmental impacts might increase variability in community structure and beta diversity. Increase in beta diversity as expressed by greater dispersion of sites in multivariate space suggests that these areas are dependent on nearby species pools, possibly primary forests, and harbor a higher spatial heterogeneity in species composition. This high variability can overestimate the importance of occasional species, thus biasing the actual value of alternative LUS for biodiversity conservation.

Ocean currents structuring the mesozooplankton in the Gulf of Mannar and the Palk Bay, southeast coast of India

The Gulf of Mannar and the Palk Bay, located between India and Sri Lanka, are the two least studied marine environments in the northern Indian Ocean. We hypothesis, perceptible physical barriers that exist between the deep Gulf of Mannar and shallow Palk Bay, and seasonally reversing surface circulation patterns in the region have a concerted effect on the ecology of these oceanographically important areas. In the present study, data collected from 30 locations in the Gulf of Mannar and the Palk Bay in March 2010 (Spring Intermonsoon), September 2010 (Southwest Monsoon) and January 2011 (Northeast Monsoon) were used to investigate the role of ocean currents in molding mesozooplankton community characteristics in these, geographically closer and ecologically important transitional zones. Spatial difference in salinity was evident in the area with consistently higher values in the Gulf of Mannar as compared to the Palk Bay. The surface salinity was maximal during the Southwest Monsoon followed by the Spring Intermonsoon, and the Northeast Monsoon. These variations in salinity were closely linked with the seasonally reversing ocean currents as revealed in MIKE 21 flow model results. The mesozooplankton community dominated by copepods showed significant difference in species richness between the Gulf of Mannar (81 species) and the Palk Bay (63 species). Non-metric Multidimensional Scaling (NMDS) and Agglomerative Hierarchical Cluster Analysis (AHCA) on Bray–Curtis copepod similarity clearly estranged the Gulf of Mannar and the Palk Bay waters during the Spring Intermonsoon, and the Northeast Monsoon, attributable to the truancy of durable mixing typical of these seasons. In contrast, aided by strong currents, the increased mixing resulted in a homogenous copepod population in the Gulf of Mannar and the Palk Bay during the Southwest Monsoon. Furthermore, the indicator and dominant species analysis for copepods divulged the spatial heterogeneity in species composition during the Spring Intermonsoon and the Northeast Monsoon periods. Multivariate Redundancy Analyses showed salinity as the most important variable accountable for the observed variance in copepod distribution. In general, the copepod community in the Gulf of Mannar was composed both of coastal and offshore species whereas, coastal species largely inhabited the Palk Bay. This kind of a study depicting zooplankton community organization as governed by seasonally reversing monsoon circulation patterns forms the first record from the Indian coastal waters. The findings attain absolute significance considering its ecological implications on oceanographically transitional systems like the Gulf of Mannar, and the Palk Bay.

Diversity, Stand Characteristics and Spatial Aggregation of Tree Species in a Bangladesh Forest Ecosystem

Assessing biodiversity and the spatial structures of forest ecosystems are important for forestry and nature conservation. However, tropical forests of Bangladesh are only sparsely investigated. Here we determined biodiversity (alpha, beta and gamma), spatial species turnover and stand characteristics of one of the few remnant tropical forests in Bangladesh. Two differently protected areas of Satchari forest were compared. We recorded tree species composition, in a systematic plot design, measured diameter at breast height for each individual tree (to assess basal area), and calculated decay in similarity of tree species composition with geographical distance. The distance-decay was assessed separately for the whole study area and for two subsamples from Satchari National Park and Satchari Reserve Forest. Satchari National Park (strictly protected) had, despite its smaller area, a higher Alpha and Gamma diversity, but a lower Beta diversity than Satchari Reserve Forest. Variation in species composition was not significant between the two differently protected areas. Basal area increased significantly with protection status although tree individuals were of equal size in both areas. Plots in the Reserve Forest were associated with higher species turnover than in the National Park. We suggest anthropogenic disturbance, which occurs in the less strictly protected Reserve Forest, is the main driver for the detected spatial heterogeneity in species composition.

Long-term effect of coral transplantation: Restoration goals and the choice of species

The transplantation is an important method for the restoration of degraded ecosystem. However, it is unclear how the choice of species and transplantation mode affects the community dynamics during recovery from a disaster, particularly for long-lived organisms such as corals. To address this issue, we study a population dynamic model of multiple species in multiple habitats connected by larval dispersal. We first consider two species showing the trade-off relationship between growth rate and mortality and examine three restoration goals to evaluate the effectiveness of transplantation: (1) total coverage; (2) species diversity; (3) spatial heterogeneity of species composition. To promote the rapid development of total coverage, the transplantation of fast-growing species should be adopted. To maintain a high level of regional species diversity, the transplantation of slow-growing species or short-dispersal species is effective. Next, we suppose four genera of corals – Acropora, Pocillopora, Porites, and Favites – as an example of coral community in Okinawa where Pocillopora is facing to local extinction. In addition to three indexes; (4) recovery of locally endangered species is evaluated as a restoration goal. Results show that to promote the recovery of Pocillopora, the transplantation of the same species is clearly the most effective choice. In contrast, the transplantations of Acropora and Porites led to undesirable results. In summary, these results indicate that both the restoration goal and the transplanted species must be carefully selected before conducting transplantation operations.

Burning history, time of burning, and year effects on plant community structure and heterogeneity in Fescue Prairie

Structure, as well as spatial and temporal heterogeneity in plant species composition were studied in a Festuca hallii (Vasey) Piper – dominated Prairie in Canada for 6 years following burning before, during, or after the growing season on sites burned 1× or 3×. Structure, spatial heterogeneity, and temporal heterogeneity were never (P > 0.05) influenced by the time of burning. Diversity and richness of graminoids, perennial forbs, and shrubs fluctuated among years after burning, but were unaffected by burning history. Excepting shrubs, canopy cover of plant functional groups positively correlated with precipitation. After a single burn, spatial heterogeneity in species composition increased with years after burning, indicating plant communities were becoming patchier, whereas those burned 3× did not change predictably through time. Spatial heterogeneity in species composition between consecutive years was positively correlated, but temporal heterogeneity in species composition did not correlate with spatial heterogeneity. Burning history and precipitation appear important in controlling the plant community structure and spatial heterogeneity in species composition in Fescue Prairie.

Do vegetation patch spatial patterns disrupt the spatial organization of plant species?

The mechanisms that structure plant diversity and generate long-range correlated spatial patterns have important implications for the conservation of fragmented landscapes. The ability to disperse and persist influences a plant species’ capacity for spatial organization, which can play a critical role in structuring plant diversity in metacommunities. This study examined the spatial patterns of species diversity within a network of patches in Cabo de Gata Natural Park, southeastern Spain. The objectives were to understand how the spatial heterogeneity of species composition (beta diversity) varies in a structured landscape, and how the long-range spatial autocorrelation of plant species is affected by the spatial configuration of patches. The mechanisms underlying the spatial distribution of plants acted at two scales. Between patches, spatial variation in species distributions was greater than that expected based on spatial randomization, which indicated that movement among patches was restricted. Within patches, diffusion processes reduced spatial variability in species distributions, and the effect was more prominent in large patches. Small patch size negatively influenced the long-range spatial autocorrelation of characteristic species, whereas inter-patch distance had a stronger effect on species frequency than it had on the disruption of spatial organized patterns. The long-range spatial autocorrelation was evaluated based on the dispersal abilities of the species. Among the 106 species evaluated, 39% of the woody species, 17% of the forbs, and 12% of the grasses exhibited disrupted long-range spatial autocorrelation where patches were small. The species that are more vulnerable to the effects of fragmentation tended to be those that have restricted dispersal, such as those that have short-range dispersal (atelechoric), e.g., Phlomis purpurea, Cistus albidus, Teucrium pseudochamaepytis, Brachypodium retusum, and the ballistic species, Genista spartioides. Helianthemum almeriense is another vulnerable species that has actively restricted dispersal (antitelechory), which is common in arid regions. Wind dispersers such as Launaea lanifera were less vulnerable to the effects of fragmentation. Long-distance dispersers whose persistence depends on facilitative interactions with other individuals, e.g., allogamous species such as Thymus hyemalis, Ballota hirsuta, and Anthyllis cytisoides, exhibit disrupted long-range spatial autocorrelation when patch size is reduced.

Spatial Structure of Forest Lepidopteran Communities in Oak Hickory Forests of Indiana

The response of forest insect communities to disturbances such as timber harvest will likely depend on the underlying spatial structure of species assemblages before the disturbance occurs. Unfortunately, many studies of forest management implicitly assume homogeneity of community structure before harvest; postlogging communities are inferred to be a direct product of the imposed management. The goal of this study is to examine variation in the community structure of forest Lepidoptera using the pretimber harvest data on Lepidoptera from 20 forest sites within three watersheds at Morgan Monroe State Forest, IN. A total of 14,537 individuals representing 324 species of Lepidoptera were sampled from Morgan-Monroe State Forest in 2007. Sampling efficiency was not a function of management unit, and, surprisingly, we found little evidence that management units differed in overall community composition. Diversity partitioning suggested that >99% of Simpson diversity (species dominance) was determined at the local scale, and each site contained the same 10 dominant taxa in rank order. Variation in species richness seemed to be more a problem of sampling bias than underlying differences in habitat preference by moth feeding guilds. Finally, Mantel tests suggested that forest moth communities at Morgan-Monroe are not spatially autocorrelated. The results here are encouraging because they strongly suggest that shifts in lepidopteran community structure should reflect the community response to disturbance rather than inherent spatial heterogeneity of species composition.

Spatial Structure of Forest Lepidopteran Communities in Oak Hickory Forests of Indiana

The response of forest insect communities to disturbances such as timber harvest will likely depend on the underlying spatial structure of species assemblages before the disturbance occurs. Unfortunately, many studies of forest management implicitly assume homogeneity of community structure before harvest; postlogging communities are inferred to be a direct product of the imposed management. The goal of this study is to examine variation in the community structure of forest Lepidoptera using the pretimber harvest data on Lepidoptera from 20 forest sites within three watersheds at Morgan Monroe State Forest, IN. A total of 14,537 individuals representing 324 species of Lepidoptera were sampled from Morgan-Monroe State Forest in 2007. Sampling efficiency was not a function of management unit, and, surprisingly, we found little evidence that management units differed in overall community composition. Diversity partitioning suggested that > 99% of Simpson diversity (species dominance) was determined at the local scale, and each site contained the same 10 dominant taxa in rank order. Variation in species richness seemed to be more a problem of sampling bias than underlying differences in habitat preference by moth feeding guilds. Finally, Mantel tests suggested that forest moth communities at Morgan-Monroe are not spatially autocorrelated. The results here are encouraging because they strongly suggest that shifts in lepidopteran community structure should reflect the community response to disturbance rather than inherent spatial heterogeneity of species composition.

Assessment of species diversity from species abundance distributions at different localities

We show how the spatial structure of species diversity can be analyzed using the correlation between the log abundances of the species in the communities, assuming that two communities at different localities can be described by a bivariate lognormal species abundance distribution. A useful property of this approach is that the log abundances of the species at two localities can be considered as samples from a bivariate normal distribution defined by only five parameters. The variances and the correlation can be estimated by maximum likelihood methods even if there is no information about the sampling intensity and the number of unobserved species. This method also enables estimation of over‐dispersion in the sampling relative to a Poisson distribution that allows sampling adjustment of the estimate of β‐diversity. Furthermore, we also obtain a partitioning of species diversity into additive components of α‐, β‐ and γ‐diversity. For instance, if the correlation between the log abundances of the species is close to one, the same species will be common and rare in the two communities and the β‐diversity will be low. We illustrate this approach by analysing similarities of communities of rare and endangered species of oak‐living beetles in south‐eastern Norway. The number of recorded species was estimated to be only 48.1% of the total number of species actually present in these communities. The correlations among communities dropped rather quickly with distance with a scaling of order 200 km. This illustrates large spatial heterogeneity in species composition, which should be accounted for in the design of schemes of such devices for assessing species diversity in these habitat‐types.

SPATIAL AND TEMPORAL PATTERNS OF SEED DISPERSAL: AN IMPORTANT DETERMINANT OF GRASSLAND INVASION

We measured spatial and temporal patterns of seed dispersal and seedling recruitment for 58 species in a grassland community to test whether seed dispersal could predict patterns of invasion after disturbance. For the 12 most abundant grasses, recruitment of native species was dependent on the propagule supply of both native and exotic species. Variability in seed rain on small spatial (1-10 m) and temporal (within season) scales led to qualitative differences in the outcome of disturbance colonization such that native species dominated disturbances when exotic seed supply was low but failed to establish when exotic seed supply was high. Local dispersal and spatial heterogeneity in species composition promoted coexistence of native and exotic species by creating refuges from high exotic seed supply within native dominated patches. Despite this, copious exotic seed production strongly limited recruitment of native species in exotic dominated patches. Most grasslands in California are presently dominated by exotic species, suggesting that competition at the seedling stage is a major barrier to native species restoration.