Ant communities,environmental characteristics and their implications for conservation in the Brazilian Pantanal

Studies about processes determining biodiversity in Pantanal are urgently needed and the use of invertebrates for this purpose may be an efficient tool. The purpose of this paper is to verify whether ants could be used to predict human impacts on Pantanal, assessing how environmental characteristics of gallery forest influence arboreal ant species richness. Specifically, we tested the hypotheses that: (i) resource availability (estimated by tree density) and (ii) diversity of environmental conditions (estimated by structural heterogeneity) positively influence arboreal ant species richness and composition. Ants were sampled in a gallery forest in the Miranda River. Ant species richness did not respond to tree density, but increased with structural heterogeneity. Species composition was affected both by tree density and structural heterogeneity. The species list produced in the present study showed a high similarity between arboreal ant faunas of Cerrado and Pantanal, which are contiguous biomes. The relationship of ant species richness with heterogeneity, as well as the observed changes of species composition with tree density and heterogeneity may be explained by the presence of a variation of environmental conditions, which create several micro-habitats in the forest. The response of the ant community can reflect human impacts on the forests of the studied region, which are usually modified to create patches for sport fishing and by pathways used in ecotourism.     

Foliage-dwelling ants in a neotropical savanna: effects of plant and insect exudates on ant communities

Ant dominance in tropical ecosystems can be explained by a capacity to exploit liquid foods such as extrafloral nectaries (EFNs) and secretions from honeydew-producing hemipterans (HPHs). Such nutritious exudates may determine ant distribution in space and shape specialization in ant–plant interactions. We provide a first assessment of how EFNs and HPHs mediate the structure of ant assemblages, ant visitation intensity, and characteristics of ant–plant interaction networks across space in Brazilian “cerrado” savanna. We used arboreal pitfall traps to sample visiting ants in four cerrado localities and recorded the presence of lepidopteran larvae to determine their possible response to ant visitation. Ant species composition and richness did not differ regardless of the presence of liquid rewards on plants, and most network patterns did not show consistent differences. However, in two of the four sites, ant densities were higher on plants with HPHs or EFNs due to increased activity by Camponotus and Pseudomyrmex ants. At these two sites, plants with liquid food sources had a more specific ant assemblage (higher specialization d′) than did plants without resources, and caterpillars were more frequently found on plants with fewer workers of Camponotus and Pseudomyrmex. Plants with HPHs had increased ant visitation and accumulated more ant species than did plants with EFNs or without liquid foods. Ant response to such food sources may thus depend on local conditions and identity of ant species, and may determine how ant assemblages are structured. Results highlight how different patterns of ant visitation to liquid resources can produce distinctive effects on herbivore infestation.     

Do lianas shape ant communities in an early successional tropical forest?

Almost half of lowland tropical forests are at various stages of regeneration following deforestation or fragmentation. Changes in tree communities along successional gradients have predictable bottom‐up effects on consumers. Liana (woody vine) assemblages also change with succession, but their effects on animal succession remain unexplored. Here we used a large‐scale liana removal experiment across a forest successional chronosequence (7–31 years) to determine the importance of lianas to ant community structure. We conducted 1,088 surveys of ants foraging on and living in trees using tree trunk baiting and hand‐collecting techniques at 34 paired forest plots, half of which had all lianas removed. Ant species composition, β‐diversity, and species richness were not affected by liana removal; however, ant species co‐occurrence (the coexistence of two or more species in a single tree) was more frequent in control plots, where lianas were present, versus removal plots. Forest stand age had a larger effect on ant community structure than the presence of lianas. Mean ant species richness in a forest plot increased by ca. 10% with increasing forest age across the 31‐year chronosequence. Ant surveys from forest >20 years old included more canopy specialists and fewer ground‐nesting ant species versus those from forests <20 years old. Consequently, lianas had a minimal effect on arboreal ant communities in this early successional forest, where rapidly changing tree community structure was more important to ant species richness and composition.     

Ants of Three Adjacent Habitats of a Transition Region Between the Cerrado and Caatinga Biomes: The Effects of Heterogeneity and Variation in Canopy Cover

Habitat heterogeneity and complexity associated with variations in climatic conditions are important factors determining the structure of ant communities in different terrestrial ecosystems. The objective of this study was to describe the horizontal and vertical distribution patterns of the ant community associated with three adjacent habitats in a transition area between the Cerrado and Caatinga biomes at the Pandeiros River, state of Minas Gerais, Brazil. We tested the following hypotheses: (1) the richness and composition of ant species and functional group structure changes between different habitats and strata; (2) habitats with higher tree species richness and density support higher ant species richness; and (3) habitats with lower variation in canopy cover support higher ant species richness. Sampling was conducted in three adjacent habitats and at three vertical strata. Ant species richness was significantly different among vertical strata. Ant species composition was different among both habitats and vertical strata and functional group structure was divergent among habitats. Partitioning of the diversity revealed that the diversity for the three components was statistically different from the one expected by the null model; α and β ₂ were higher and β ₁ was lower than the values expected by chance. Tree density and variation in canopy cover negatively affected ant species richness. The occurrence of different species and the changing of functional group structures in different habitats and strata suggest an ecological–evolutionary relationship between ants and their habitats and emphasize the need to implement local conservation strategies in the ecotones between biomes.     

Biodiversity responses to land‐use and restoration in a global biodiversity hotspot: Ant communities in Brazilian Cerrado

Given that land‐use change is the main cause of global biodiversity decline, there is widespread interest in adopting land‐use practices that maintain high levels of biodiversity, and in restoring degraded land that previously had high biodiversity value. In this study, we use ant taxonomic and functional diversity to examine the effects of different land uses (agriculture, pastoralism, silviculture and conservation) and restoration practices on Cerrado (Brazilian savanna) biodiversity. We also examine the extent to which ant diversity and composition can be explained by vegetation attributes that apply across the full land management spectrum. We surveyed vegetation attributes and ant communities in five replicate plots of each of 13 land‐use and restoration treatments, including two types of native vegetation as reference sites: cerrado sensu stricto and cerradão. Several land‐use and restoration treatments had comparable plot richness to that of the native reference habitats. Ant species and functional composition varied systematically among land‐use treatments following a gradient from open habitats such as agricultural fields to forested sites. Tree basal area and grass cover were the strongest predictors of ant species richness. Losses in ant diversity were higher in land‐use systems that transform vegetation structure. Among productive systems, therefore, uncleared pastures and old pine plantations had similar species composition to that occurring in cerrado sensu stricto. Restoration techniques currently applied to sites that were previously Cerrado have focused on returning tree cover, and have failed to restore ant communities typical of savanna. To improve restoration outcomes for Cerrado biodiversity, greater attention needs to be paid to the re‐establishment and maintenance of the grass layer, which requires frequent fire. At the broader scale, conservation planning in agricultural landscapes, should recognize the value of land‐use mosaics and the risks of homogenization.     

Flower-heads, herbivores, and their parasitoids: food web structure along a fertility gradient

Abstract. 1. The ways in which a soil fertility gradient affects three trophic level food webs defined by plants of the family Asteraceae, flower‐head herbivores, and their parasitoids was investigated. It was tested how the fertility gradient alters: (i) the abundance and richness of plants, herbivores, and their parasitoids, (ii) the herbivore–plant ratio, and (iii) the connectance of the plant–herbivore community matrix. 2. From April to May 2000, plants and insects were sampled in 16 Brazilian Cerrado (sensu stricto) sites along a physiognomic gradient varying from open shrublands (cerrado) to closed woodlands (cerradão). Sites were objectively positioned along the physiognomic gradient by a single index, tree density. Sixty‐seven per cent of the variation in tree density among sites was correlated to two principal components of a PCA, representing gradients of soil fertility. 3. Asteraceae abundance, richness, and flower‐head availability were negatively related to tree density due to their preference for sunny environments, despite the surplus of soil nutrients. The abundance and richness of Diptera and Lepidoptera, the most important flower‐head herbivores, were also negatively related to tree density. Parasitoid abundance decreased with tree density; however, the number of parasitoids per hosts was lower in cerrado, suggesting that top‐down forces are not getting stronger in more productive sites, as could be expected. 4. Community allometry analyses showed that the herbivore to plant ratio was independent of community richness and did not respond to tree density. 5. Connectance of the plant–herbivore matrix was dependent on the community matrix size. Proportionally, species‐rich cerrado sites had fewer interactions than their species‐poor counterparts. Nevertheless, after removing the effect of the matrix size, connectance was not related to tree density. 6. Soil fertility, as the primary cause of the cerrado–cerradão physiognomic gradient, strongly affected the abundance and richness of plants, herbivores and their parasitoids; however, it had little effect on important community attributes, such as the herbivore–plant ratio and the connectance of the plant–herbivore matrix.     

Effects of habitat complexity on ant assemblages

We investigated responses of ant communities to habitat complexity, with the aim of assessing complexity as a useful surrogate for ant species diversity. We used pitfall traps to sample ants at twenty-eight sites, fourteen each of low and high habitat complexity, spread over ca 12 km in Sydney sandstone ridge-top woodland in Australia. Ant species richness was higher in low complexity areas, and negatively associated with ground herb cover, tree canopy cover, soil moisture and leaf litter. Ant community composition was affected by habitat complexity, with morphospecies from the genera Monomorium, Rhytidoponera and Meranoplus being the most significant contributors to compositional differences. Functional group responses to anthropogenic disturbance may be facilitated by local changes in habitat complexity. Habitat complexity, measured as a function of differences in multiple strata in forests, may be of great worth as a surrogate for the diversity of a range of arthropod groups including ants.     

Extrafloral nectar as a driver of arboreal ant communities at the site‐scale in Brazilian savanna

Despite years of study, it remains unclear if and to what extent the effects of extra‐floral nectaries (EFNs) on arboreal ants observed on individual trees scale up to larger spatial scales. Here, we address this issue in Brazilian savanna and tested three predictions: (i) Trees with EFN have higher richness of arboreal ant species than trees without; (ii) Arboreal ant species richness increases with the proportion of total EFN‐bearing trees at the site scale, due to a higher occurrence of non‐core ant species; (iii) Ant species composition changes with the proportion of EFN‐bearing trees at the site scale. We sampled arboreal ants in 32 plots with EFN‐bearing trees ranging from 0% to 60% of all trees. We sampled 72 ant species, from which 17 (mostly belonging to Camponotus, Cephalotes and Crematogaster) were identified as core species in at least one of the ant‐EFN networks in the 32 plots. Ant species richness was significantly higher on EFN‐bearing trees. We identified 11 ant species that preferentially occurred on EFN‐bearing trees, all of which were core partners in networks. Species richness at the site scales increased with the proportion of EFN‐bearing trees, regardless of tree density and richness; this pattern was due to a higher occurrence of non‐core ant species. Finally, species composition also varied with the proportion of EFN‐bearing trees. Therefore, we found that the presence of EFNs not only influences arboreal ants on individual trees but also has a substantial effect on the ant‐EFN network on a broader community scale. The increase in non‐core species site scale reveals that this interaction is unlikely to result in substantially enhanced protection services for EFN‐bearing plants.     

Fern richness,tree species surrogacy,and fragment complementarity in a Mexican tropical montane cloud forest

We related pteridophytes versus tree species composition to identify surrogate measures of diversity, and complementarity of seven cloud forest fragments. Forest structure, and fern and tree composition were determined in 70 (2 × 50 m) transects. Fern density (10,150–25,080 individuals/ha) differed among sites. We recorded 83 fern species in the transects. Nonparametric richness estimators indicated that more sampling effort was needed to complete fern inventories (14 more species). However, ferns recorded outside of the transects increased richness to 103 species (six more species than predicted). Twenty-eight species were unique and rare due to special habitat requirements (Diplazium expansum, Hymenophyllum hirsutum, Melpomene leptostoma, Terpsichore asplenifolia), or were at a geographical distribution edge (Diplazium plantaginifolium, Lycopodium thyoides, Pecluma consimilis, Polypodium puberulum). Correlations between fern richness and tree richness and density were not significant, but were significant between fern richness and fern density, between epiphytic fern density and tree richness and density. Tree richness is not a good surrogate for fern diversity. Only three species were recorded in all fragments (Polypodium lepidotrichum, P. longepinnulatum, P. plebeium); thus fragments pteridophytes compositions are highly complementary, but more similar for ferns than for trees. A regional conservation approach which includes many small reserves needs to focus supplementarity on patterns of tree and fern species richness.     

Ants and people: a test of two mechanisms potentially responsible for the large‐scale human population–biodiversity correlation for Formicidae in Europe

Aim: Recent coarse‐scale studies have shown positive relationships between the biodiversity of plants/vertebrates and the human population. Little is known about the generality of the pattern for invertebrates. Moreover, biodiversity and human population might correlate because they both covary with other factors such as energy availability and habitat heterogeneity. Here we test these two non‐mutually exclusive mechanisms with ant species‐richness data from the Fauna Europaea. Location Forty‐three European countries/regions. Methods We derived mixed models of total, native and exotic ant species richness as a function of human population size/density, controlling for country area, plant species richness (as a proxy for habitat heterogeneity), and mean annual temperature and precipitation (variables related to energy availability). Results Ant species richness increased significantly with increasing human population. This result was confirmed when controlling for variations in country area. Both for human population size/density and for ant species richness, there were positive correlations with temperature but not with precipitation. This finding is in agreement with the energy‐availability hypothesis. However, we observed a negative latitudinal gradient in ant and plant species richness, although not in human population size/density. Plant species richness was positively correlated with ant species richness but not with human population size/density. Thus, there is evidence that this type of habitat heterogeneity can play a role in the observed latitudinal gradient of ant species richness, but not in the positive correlation between ant species richness and human population. The results were confirmed for the 545 native and the 32 exotic ant species reported, and we observed a good correlation between exotic and native ant species richness. Main conclusions Ant species richness in European countries conforms to six macroecological patterns: (1) a negative latitudinal gradient; and a positive (2) species–energy relationship, (3) species–area relationship, (4) correlation with plant species richness, (5) exotic–native species richness correlation, and (6) species–people correlation. There is some evidence for the energy‐availability hypothesis, but little evidence for habitat heterogeneity as an explanation of the large‐scale human population–ant biodiversity correlation. This correlation has implications for the conservation of ant diversity in Europe.     

Tree species richness and density affect parasitoid diversity in cacao agroforestry

In Brazil, cacao is mostly planted beneath shade trees. The diversity of shade trees varies from monospecific to highly diverse canopies, characteristic of pristine Atlantic Forest. This study evaluates the relationships between family richness of Hymenoptera-Parasitica and Chrysidoidea, and tree species richness and density, the species richness of herbaceous understorey, and the area and age of the cacao agroforestry system. We sampled 16 cacao agroforestry systems, with canopy diversity ranging from one to 22 tree species per hectare, in three seasons: summer (March), winter (August) and spring (November). Parasitoids were sampled using eight Malaise-Townes traps per site. Tree species richness and density were enumerated within 1 ha at each site, and herbaceous plant species richness was calculated in eight 1 m² plots, within the hectare. The number of parasitoid families increased with tree species richness and density in spring and summer, but decreased in winter. Neither species richness of herbaceous plants nor area and age of the system affected parasitoid family richness. We suggest that the increase of parasitoid diversity with tree species richness and density in warmer seasons reflects increasing heterogeneity and availability of resources. The decrease in parasitoid family number with tree density in winter may be due to local impoverishment of resources, leading to parasitoid emigration to neighbouring forest remnants. This result implies that a higher diversity of shade trees will help to maintain high parasitoid levels and, in consequence, higher levels of natural enemies of cacao pests, particularly in the warmer seasons. This prediction is borne out in the experience of cacao producers. The proper management of shade tree diversity will play a vital role in maintaining the sustainability of cacao agroforestry production systems in the tropics and, concurrently, will maintain high biodiversity values in these locations.     

Secondary seed dispersal by ants in Neotropical cerrado savanna: species‐specific effects on seeds and seedlings of Siparuna guianensis (Siparunaceae)

1. Most woody plant species in tropical habitats are primarily vertebrate‐dispersed, but interactions between ants and fallen seeds and fruits are frequent. This study assesses the species‐specific services provided by ants to fallen arillate seeds of Siparuna guianensis, a primarily bird‐dispersed tree in cerrado savanna. The questions of which species interact with fallen seeds, their relative contribution (versus vertebrates) to seed removal, and the potential effects on seedling establishment are investigated. 2. Seeds are removed in similar quantities in caged and control treatments, suggesting that ants are the main dispersers on the ground. Five ant species attended seeds. Pheidole megacephala (≈0.4 cm) cooperatively transported seeds, whereas the smaller Pheidole sp. removed the seed aril on spot. Large (> 1.0 cm) Odontomachus chelifer, Pachycondyla striata, and Ectatomma edentatum individually carried seeds up to 4 m. Bits of aril are fed to larvae and intact seeds are discarded near the nest entrance. 3. Overall, greater numbers of seedlings were recorded near ant nests than in control plots without nests. This effect, however, was only detected near P. megacephala and P. striata nests, where soil penetrability was greater compared with controls. Soil nutrients did not differ between paired plots. 4. This study confirms the prevalence of ant–seed interactions in cerrado and shows that ant‐derived benefits are species‐specific. Ant services range from seed cleaning on the spot to seed displacement promoting non‐random spatial seedling recruitment. Although seed dispersal distances by ants are likely to be shorter than those by birds, our study of S. guianensis shows that fine‐scale ant‐induced seed movements may ultimately enhance plant regeneration in cerrado.     

Experimental small-scale grassland fragmentation alters competitive interactions among ant species

Different species may respond differently to habitat fragmentation. Theory predicts that abundant generalist species should be less affected by fragmentation than specialist species. In ant communities, the most abundant species is often behaviourally dominant. Thus, habitat fragmentation could alter competitive interactions between the dominant ant species and the other species. We tested this hypothesis in a long-term grassland fragmentation experiment. Fragments of different size (20.25 and 2.25 m²) were isolated by a 5-m wide strip of frequently mown vegetation. Control plots were situated in adjacent undisturbed grassland. Ant density and species composition were assessed 3 and 6 years after initiation of the experimental fragmentation. The effect of the dominant ant species on the resource use of the other species was examined at natural sugar resources (aphids and extrafloral nectaries) and at artificial sugar baits. Lasius paralienus was the most abundant ant species (72% of nests) in the grasslands examined. Species richness and forager density in the other species decreased with increasing density of L. paralienus in fragments but not in control plots. The overall forager density of the other species was positively related to their habitat niche overlap with L. paralienus. The density of foragers of the other species at sugar resources was not affected by L. paralienus forager density. The experimental fragmentation resulted in an increase in natural sugar resources in fragments. This may have reduced the intensity of interspecific competition for sugar resources. Our study shows that the grassland fragmentation altered interactions between the dominant L. paralienus and the other ant species.Electronic Supplementary Material Supplementary material is available for this article at     

The invasive Yellow Crazy Ant and the decline of forest ant diversity in Indonesian cacao agroforests

Throughout the tropics, agroforests are often the only remaining habitat with a considerable tree cover. Agroforestry systems can support high numbers of species and are therefore frequently heralded as the future for tropical biodiversity conservation. However, anthropogenic habitat modification can facilitate species invasions that may suppress native fauna. We compared the ant fauna of lower canopy trees in natural rainforest sites with that of cacao trees in agroforests in Central Sulawesi, Indonesia in order to assess the effects of agroforestry on occurrence of the Yellow Crazy Ant Anoplolepis gracilipes, a common invasive species in the area, and its effects on overall ant richness. The agroforests differed in the type of shade-tree composition, tree density, canopy cover, and distance to the village. On average, 43% of the species in agroforests also occurred in the lower canopy of nearby primary forest and the number of forest ant species that occurred on cacao trees was not related to agroforestry characteristics. However, A. gracilipes was the most common non-forest ant species, and forest ant richness decreased significantly with the presence of this species. Our results indicate that agroforestry may have promoted the occurrence of A. gracilipes, possibly because tree management in agroforests negatively affects ant species that depend on trees for nesting and foraging, whereas A. gracilipes is a generalist when it comes to nesting sites and food preference. Thus, agroforestry management that includes the thinning of tree stands can facilitate ant invasions, thereby threatening the potential of cultivated land for the conservation of tropical ant diversity.     

Vegetation structure determines insect herbivore diversity in seasonally dry tropical forests

Vegetation structure can often determine insect herbivore fauna in forests, but this mechanism has been demonstrated in seasonally dry tropical forests (SDTFs) only at small spatial scales. In this study we evaluated the effects of the geographical location of SDTFs and vegetation structure on insect herbivore communities (leaf-chewing and sap-sucking guilds) in three Brazilian ecoregions (Cerrado, Cerrado/Caatinga transition, and Caatinga). We tested the following predictions: (1) insect herbivore species composition, richness, abundance and beta diversity differ among forests in different ecoregions; (2) insect richness, abundance and beta diversity are positively related to tree richness and density; (3) spatial turnover of species is the primary mechanism that generates herbivorous insect β-diversity in different ecoregions, and is positively influenced by tree richness. The composition, richness, and abundance of herbivorous insects differed over SDFs along the gradient of Cerrado and Caatinga. Both herbivore guilds responded positively to tree richness. Tree density only determined the richness and abundance of sap-sucking herbivores. Insect β-diversity was similar among Cerrado and transition areas, but lower in Caatinga itself; β-diversity was also positively affected by tree richness. Species turnover, as opposed to nestedness, was the main mechanism generating β-diversity, but itself was not related to tree richness. We demonstrate in this study the importance of landscape diversity and availability of local resources for herbivorous insect communities, and we emphasize the importance of SDTF conservation in different ecoregions as a result of species turnover.     

Energy, Density, and Constraints to Species Richness: Ant Assemblages along a Productivity Gradient

Species richness describes the number of species of a given taxon in a given time and space. The energy limitation hypothesis links the species richness of consumer taxa to net primary productivity (NPP) through two relationships: NPP limits a taxon's density, and taxon density limits species richness. We study both relationships with a survey of 15 ground ant assemblages, along a productivity gradient from deserts to rain forests. Ant density (colonies m-2) was a positive, decelerating function of net aboveground productivity (NAP). A stepwise regression suggests that the efficiency with which NAP is converted to ant colonies increases with maximum summer temperature and decreases with precipitation. Ant species richness was a positive decelerating function of density at three spatial scales. This supports the energy limitation hypothesis' assumption that average population densities are higher in environments that are more productive. These two nonlinear functions (NAP-density and density-species richness) combine to create, at a variety of scales, positive, decelerating, productivity-diversity curves for a common, ecologically dominant taxon across the terrestrial productivity gradient. However, variance in the density and diversity explained by NAP decreases with scale, suggesting that energy limitation of diversity predominates at small spatial scales (<1 ha).     

Ant assemblages on rehabilitated tropical landfills

Ant assemblages have been used widely throughout the world except in Asia to assess land restoration. In this study, ant assemblages were studied on three rehabilitated landfills (closed for 11–26 years) and a mature woodland as reference in Hong Kong. Grassland and woodland areas on each landfill were examined separately. Ants were sampled by soil extraction, litter extraction and pitfall trapping to maximize capture efficiency. Simple vegetation measurements were also taken. A total of 64 ant species from 33 genera were recorded. Ant species richness in the three landfills was similar (25–30 species), which did not correlate with the age of rehabilitation. A relationship between ant species richness and various vegetation parameters was not observed. Cluster analysis separated the landfill sites from the reference site, and grassland sites from woodland sites. Composition of ants based on functional grouping differed on the grassland and woodland sites, and functional group composition also separated the landfill sites from the reference site. Ant functional groups but not species richness showed a successional pattern with the ecological development of landfills. However, even after more than 25 years of rehabilitation, the ant assemblages on landfills were still very different from that on the reference site.     

Factors influencing epiphytic bryophyte and lichen species richness at different spatial scales in managed temperate forests

The effect of management related factors on species richness of epiphytic bryophytes and lichens was studied in managed deciduous-coniferous mixed forests in Western-Hungary. At the stand level, the potential explanatory variables were tree species composition, stand structure, microclimate and light conditions, landscape and historical variables; while at tree level host tree species, tree size and light were studied. Species richness of the two epiphyte groups was positively correlated. Both for lichen and bryophyte plot level richness, the composition and diversity of tree species and the abundance of shrub layer were the most influential positive factors. Besides, for bryophytes the presence of large trees, while for lichens amount and heterogeneity of light were important. Tree level richness was mainly determined by host tree species for both groups. For bryophytes oaks, while for lichens oaks and hornbeam turned out the most favourable hosts. Tree size generally increased tree level species richness, except on pine for bryophytes and on hornbeam for lichens. The key variables for epiphytic diversity of the region were directly influenced by recent forest management; historical and landscape variables were not influential. Forest management oriented to the conservation of epiphytes should focus on: (i) the maintenance of tree species diversity in mixed stands; (ii) increment the proportion of deciduous trees (mainly oaks); (iii) conserving large trees within the stands; (iv) providing the presence of shrub and regeneration layer; (v) creating heterogeneous light conditions. For these purposes tree selection and selective cutting management seem more appropriate than shelterwood system.     

Understory vegetation response to mountain pine beetle disturbance in northern Colorado lodgepole pine forests

Understory plants are an important element of forests, having a considerable influence on ecosystem functioning and canopy-tree development following disturbance. Recent bark beetle outbreaks across western North American forests have caused extensive canopy mortality, creating new growing conditions that provide the opportunity for changes within the intact understory. Over a five-year period following peak mountain pine beetle (MPB) activity across lodgepole pine-dominated forests in Rocky Mountain National Park, Colorado, we measured the changes in plant diversity, cover, and dominance by lifeform and quantified tree regeneration rates. Average species richness and diversity increased, but overall plant cover did not change. Graminoids appeared to benefit the most, increasing in average cover, richness, and relative dominance. The rise in graminoid dominance was largely at the expense of shrubs, which showed little ability to benefit from overstory mortality within the first years following attack. Most plant responses were positively related to the total tree basal area lost since the peak of the outbreak, suggesting that increased resource availability following tree death may benefit understory plants. However, a negative relationship between several understory variables and tree sapling density provides evidence that understory plants compete with saplings for the newly available resources. Tree seedling density nearly doubled over the duration of the study, indicating a strong regeneration pulse. Among species, lodgepole pine displayed the greatest tree seedling establishment. This is one of the first studies to use repeated measurements to describe this often-overlooked component of forest change associated with MPB disturbance.

     

Ants as indicators for vertebrate fauna at a local scale: an assessment of cross-taxa surrogacy in a disturbed matrix

We examined the spatial fidelity in the pattern in species richness, abundance and composition of ants, birds, mammals and reptiles in a Eucalyptus vegetation type in Australian tropical savanna woodland. We sampled 32 sites representing intact (uncleared) vegetation, and three treatments of different clearing age (2, 12 and 18 years). We investigated whether each fauna taxon could act a surrogate for pattern in the other, and whether they responded in parallel to time since clearing. Reptiles and mammals were combined into a single group. The correlation between taxa was low for abundance (the best being between rept/mamm and ant abundance R = 0.34) and moderate for species richness (varied from 0.36 to 0.44). Mantel tests identified a moderately strong relationship between bird and rept/mamm composition (R = 0.48). Recent clearing (2–12 years) depleted both abundance and species richness of the vertebrate fauna, whereas ant abundance spiked. Ant species richness was consistent over time since clearing. ANOSIM revealed that clearing age was a strong a priori predictor of birds and rept/mamm composition (Global R = 0.48, 0.65, respectively), whereas it was not for ants (Global R = 0.20). Pair-wise comparisons suggested that for birds, rept/mamm, there was consistent changes in composition from intact woodlands to different aged clearing. This was not the case for ants; most distinct variation in composition occurred between treatments of increasing in clearing age (2–18 years R = 0.69, 12–18 years R = 0.65). The results of this study do not support the use of ants as a surrogate of vertebrates at a local scale in a cleared and intact vegetation mosaic. We acknowledge that identification of universal surrogates and indicators are difficult to find, but funding and political expediency that demand rapid solutions to conservation planning necessitate continued investigation of the merits of using surrogate species.