Vertebrate Exclusion Research Articles

Do Ground-Dwelling Vertebrates Promote Diversity in a Neotropical Forest? Results from a Long-Term Exclosure Experiment.

Using a decade-long exclosure experiment in Panama, we tested the hypothesis that ground-dwelling vertebrate herbivores and seed predators are crucial determinants of tropical tree diversity and abundance within the understory. Our exclosure experiment is a community-level test of the Janzen-Connell hypothesis. Therefore, we predicted that vertebrate exclusion would (a) increase plant densities and (b) lower richness, diversity, and evenness. Excluding vertebrates caused a 38%-46% increase in plant densities, which, in contrast to our predictions, caused species richness to increase by 12%-15%. Because vertebrate exclusion causes plant species richness to increase, not decrease, vertebrates are unlikely to be causal agents of Janzen-Connell effects. We synthesized this and previous studies to explore why plant richness responds differently to defaunation and exclosures in tropical forests worldwide. Likely because of their contrasting effects on mesoconsumers, defaunation and exclosures cause decreases and increases in plant density respectively, which in turn cause corresponding changes in richness.

Episodic bamboo die‐off, neighbourhood interactions and tree seedling performance in a Patagonian mixed forest

Summary Episodic mass flowering and subsequent die‐off of bamboo understories may generate rare opportunities for tree regeneration by altering consumer–seedling interactions as much as by increasing light availability to seedlings. We hypothesized that bamboo dieback interacts with canopy neighbourhood composition in creating recruitment microsites for tree seedling species with varied shade tolerance and susceptibility to herbivory. We conducted a 2‐year experiment in a Patagonian mixed forest altered by extensive, but patchy dieback of the bamboo Chusquea culeou. Newly emerged seedlings of Nothofagus alpina (more shade‐tolerant) and Nothofagus dombeyi (less shade‐tolerant) were planted in conspecific and heterospecific canopy neighbourhoods, with either a flowered (dead) or non‐flowered (live) bamboo understorey. Seedlings were placed inside and outside mesh cages to assess mortality from vertebrate or invertebrate consumers. Vertebrate exclusion increased seedling survival regardless of bamboo condition. Seedling loss to invertebrates decreased with bamboo die‐off, resulting in higher survival of N. alpina in dead than in live patches. In contrast, bamboo die‐off increased N. dombeyi mortality by wilting, which counteracted the benefits of seedling release from consumers. Bamboo die‐off increased light availability and enhanced seedling growth for both species. Nothofagus alpina seedlings were less damaged or killed by invertebrates under heterospecific canopies than under conspecifics (associational resistance), whereas N. dombeyi performance was unaffected by neighbourhood composition. Bamboo die‐off did not change seedling performance patterns observed across canopy neighbourhoods with live bamboo understories. Synthesis. Gaps created by bamboo die‐off can exert both positive and negative, species‐specific effects on the likelihood of tree seedling establishment. We conclude that infrequent understorey disturbances coupled with canopy neighbourhood effects mediated by seedling herbivores may drive gap‐phase succession within old‐growth forests.

Eilat virus displays a narrow mosquito vector range.

BackgroundMost alphaviruses are arthropod-borne and utilize mosquitoes as vectors for transmission to susceptible vertebrate hosts. This ability to infect both mosquitoes and vertebrates is essential for maintenance of most alphaviruses in nature. A recently characterized alphavirus, Eilat virus (EILV), isolated from a pool of Anopheles coustani s.I. is unable to replicate in vertebrate cell lines. The EILV host range restriction occurs at both attachment/entry as well as genomic RNA replication levels. Here we investigated the mosquito vector range of EILV in species encompassing three genera that are responsible for maintenance of other alphaviruses in nature.MethodsSusceptibility studies were performed in four mosquito species: Aedes albopictus, A. aegypti, Anopheles gambiae, and Culex quinquefasciatus via intrathoracic and oral routes utilizing EILV and EILV expressing red fluorescent protein (−eRFP) clones. EILV-eRFP was injected at 107 PFU/mL to visualize replication in various mosquito organs at 7 days post-infection. Mosquitoes were also injected with EILV at 104-101 PFU/mosquito and virus replication was measured via plaque assays at day 7 post-infection. Lastly, mosquitoes were provided bloodmeals containing EILV-eRFP at doses of 109, 107, 105 PFU/mL, and infection and dissemination rates were determined at 14 days post-infection.ResultsAll four species were susceptible via the intrathoracic route; however, replication was 10–100 fold less than typical for most alphaviruses, and infection was limited to midgut-associated muscle tissue and salivary glands. A. albopictus was refractory to oral infection, while A. gambiae and C. quinquefasciatus were susceptible only at 109 PFU/mL dose. In contrast, A. aegypti was susceptible at both 109 and 107 PFU/mL doses, with body infection rates of 78% and 63%, and dissemination rates of 26% and 8%, respectively.ConclusionsThe exclusion of vertebrates in its maintenance cycle may have facilitated the adaptation of EILV to a single mosquito host. As a consequence, EILV displays a narrow vector range in mosquito species responsible for the maintenance of other alphaviruses in nature.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-014-0595-2) contains supplementary material, which is available to authorized users.

Complementary ecosystem services provided by pest predators and pollinators increase quantity and quality of coffee yields

Wild animals substantially support crop production by providing ecosystem services, such as pollination and natural pest control. However, the strengths of synergies between ecosystem services and their dependencies on land-use management are largely unknown. Here, we took an experimental approach to test the impact of land-use intensification on both individual and combined pollination and pest control services in coffee production systems at Mount Kilimanjaro. We established a full-factorial pollinator and vertebrate exclosure experiment along a land-use gradient from traditional homegardens (agroforestry systems), shaded coffee plantations to sun coffee plantations (total sample size = 180 coffee bushes). The exclusion of vertebrates led to a reduction in fruit set of ca 9%. Pollinators did not affect fruit set, but significantly increased fruit weight of coffee by an average of 7.4%. We found no significant decline of these ecosystem services along the land-use gradient. Pest control and pollination service were thus complementary, contributing to coffee production by affecting the quantity and quality of a major tropical cash crop across different coffee production systems at Mount Kilimanjaro.

Seed and Establishment Limitation: Effects on Plant Diversity in an Amazonian Rain Forest

AbstractRecruitment limitation (seed limitation and establishment limitation) has been proposed to contribute to the maintenance of high diversity of plants in tropical forests. This hypothesis suggests that diversity is maintained by slowing down competitive exclusion. In this study we: (1) quantified the relative importance of seed limitation and establishment limitation on recruitment for 4–7 species, testing the impact of seed predators and competition; (2) evaluated the effect of recruitment limitation on the diversity of seedling communities: if recruitment limitation is a diversity‐promoting mechanism, then removing the limitation should have a negative effect on diversity. To evaluate the magnitude and effects of recruitment limitation we used data from 400 seed traps, we executed seed addition experiments with and without vertebrate exclusion, and we conducted seedling transplant experiments during 2 yr in an Amazonian rain forest in Colombia. On the basis of seed traps, we found that seed limitation was strong; however, seed addition experiments showed that establishment limitation is more important than seed limitation for recruitment in all species considered. The addition/transplant experiments did not affect diversity of the surrounding seedlings, lending no support to the theory that recruitment limitation affects diversity. Establishment limitation was stronger at the seed–seedling transition than in older seedling transitions, as shown by high survival in the seedling transplants experiment. We found that seed dispersal increases regenerating plant diversity, and that predation is an important factor affecting seed establishment. We highlight the role of animals in these processes and therefore in the maintenance of diversity in tropical rain forests.

The influence of pollinators and seed predation on seed production in dwarf grassland Protea “sugarbushes” (Proteaceae)

Flowers of many plant species are visited by both birds and insects, making it necessary to establish their relative contributions to seed set. In Protea, available evidence points to an overwhelming preponderance of bird-pollination systems in the genus, but the scented flowers of several dwarf grassland “sugarbush” species suggest that some Protea species may be adapted for insect pollination. In this study, we used both selective exclusion of vertebrates and complete exclusion of all visitors to investigate whether the insects that visit the scented flowerheads of three Protea species (Protea dracomontana, Protea simplex and Protea welwitschii) in KwaZulu-Natal, South Africa contribute to seed production. We also performed supplemental hand pollinations to test for pollen limitation. Seed set was generally higher in inflorescences subjected to vertebrate exclusion than in those from which all visitors were excluded, suggesting that fertile cross-pollen was deposited by insects, but these differences were slight because of high levels of self-fertilization in the study species. Pollen deposition and pollen tube growth were similar for vertebrate-excluded and open-pollinated inflorescences. Supplemental hand-pollination treatments revealed that seed set in P. simplex and P. welwitschii was not pollen-limited. Overall seed set was low, typical of the family Proteaceae, and infructescences were highly predated by lepidopteran larvae. We conclude that insects are likely to contribute to seed set of the study species, but further studies using molecular markers are required to establish the actual level of insect-mediated outcrossing.

Terrestrial vertebrates alter seedling composition and richness but not diversity in an Australian tropical rain forest

Although birds and mammals play important roles in several mechanisms hypothesized to maintain plant diversity in species-rich habitats, there have been few long-term, community-level tests of their importance. We excluded terrestrial birds and mammals from fourteen 6 x 7.5 m plots in Australian primary tropical rain forest and compared recruitment and survival of tree seedlings annually over the subsequent seven years to that on nearby open plots. We re-censused a subset of the plots after 13 years of vertebrate exclusion to test for longer-term effects. After two years of exclusion, seedling abundance was significantly higher (74%) on exclosure plots and remained so at each subsequent census. Richness was significantly higher on exclosure plots from 1998 to 2003, but in 2009 richness no longer differed, and rarefied species richness was higher in the presence of vertebrates. Shannon's diversity and Pielou's evenness did not differ in any year. Vertebrates marginally increased density-dependent mortality and recruitment limitation, but neither effect was great enough to increase richness or diversity on open plots relative to exclosure plots. Terrestrial vertebrates significantly altered seedling community composition, having particularly strong impacts on members of the Lauraceae. Overall, our results highlight that interactions between terrestrial vertebrates and tropical tree recruitment may not translate into strong community-level effects on diversity, especially over the short-term, despite significant impacts on individual species that result in altered species composition.

Post-fire seed predation: Does distance to unburnt vegetation matter?

Human-induced changes to fire regimes result in smaller, more patchy fires in many peri-urban areas, with a concomitant increase in potential edge effects. In sclerophyll vegetation, many structurally dominant serotinous plants rely on the immediate post-fire environment for recruitment. However, there is little information about how fire attributes affect seed predation or recruitment for these species. We examined the influence of distance to unburnt vegetation on post-dispersal seed predation for five serotinous species from sclerophyll vegetation in the Sydney region, south-eastern Australia; Banksia serrata L.f., Banksia spinulosa Sm. var. spinulosa, Hakea gibbosa (Sm.) Cav., Hakea teretifolia (Salisb.) Britten (all Proteaceae) and Allocasuarina distyla (Vent.) L. Johnson (Casuarinaceae). We used cafeteria trials and differential exclusion of vertebrates and invertebrates to test whether rates of seed removal for these five species differed among (i) unburnt, (ii) burnt-edge (approx. 10 m from unburnt vegetation) and (iii) burnt-interior (approx. 100 m from unburnt vegetation) locations. When all animals had access to seeds, seeds were removed at lower rates from burnt-interior areas than from other locations. Vertebrates (small mammals) showed this pattern markedly the first time the experiment was run, but in a repeat trial this effect disappeared. Rate of seed removal by invertebrates differed among plant species but we did not detect any such differences for removal by vertebrates. Overall rates of seed removal also differed significantly between the two fires studied. Our results indicate that small mammal seed predation can be substantial for large-seeded serotinous shrubs, and that differences in the perimeter: area ratio, severity or size of a fire are likely to affect seed predation.

Weed seed predation increases with vegetation cover in perennial forage crops

Vegetation cover may affect weed seed predation by modifying the habitat quality for predatory organisms. Post-dispersal weed seed predation was measured by placing ‘seed cards’ in two perennial crops (alfalfa, cocksfoot) with and without crop cutting and in plots with bare soil. Each treatment was repeated four times in a randomized complete block design. Vegetation cover was measured by canopy light interception. Predation trials lasted two weeks and were repeated three times. Seed predation rates varied among three weed species (highest for Viola arvensis, intermediate for Alopecurus myosuroides, lowest for Sinapis arvensis). Vertebrate exclusion cages (12 mm × 12 mm openings) strongly reduced seed predation rates. Positive relationships were observed between vegetation cover and seed predation rates by both vertebrates and invertebrates for all weed species and trials, except when overall predation rates were very low. Predation rates were highest in uncut alfalfa, lowest on bare soil, but 16–64% of this variation could equally be explained by vegetation cover. The factorial design indicated that cutting had a stronger impact than crop species (legume or grass). Results suggest that weed seed predation may be enhanced by maintaining a high and temporally extended vegetation cover.

Termites, vertebrate herbivores, and the fruiting success of Acacia drepanolobium

In African savannas, vertebrate herbivores are often identified as key determinants of plant growth, survivorship, and reproduction. However, plant reproduction is likely to be the product of responses to a suite of abiotic and biotic factors, including nutrient availability and interactions with antagonists and mutualists. In a relatively simple system, we examined the role of termites (which act as ecosystem engineers--modifying physical habitat and creating islands of high soil fertility), vertebrate herbivores, and symbiotic ants, on the fruiting success of a dominant plant, Acacia drepanolobium, in East African savannas. Using observational data, large-scale experimental manipulations, and analysis of foliar N, we found that Acacia drepanolobium trees growing at the edge of termite mounds were more likely to reproduce than those growing farther away, in off-mound soils. Although vertebrate herbivores preferentially used termite mounds as demonstrated by dung deposits, long-term exclusion of mammalian grazers did not significantly reduce A. drepanolobium fruit production. Leaf N was significantly greater in trees growing next to mounds than in those growing farther away, and this pattern was unaffected by exclusion of vertebrates. Thus, soil enrichment by termites, rather than through dung and urine deposition by large herbivores, is of primary importance to fruit production near mounds. Across all mound-herbivore treatment combinations, trees that harbored Crematogaster sjostedti were more likely to fruit than those that harbored one of the other three ant species. Although C. sjostedti is less aggressive than the other ants, it tends to inhabit large, old trees near termite mounds which are more likely to fruit than smaller ones. Termites play a key role in generating patches of nutrient-rich habitat important to the reproductive success of A. drepanolobium in East African savannas. Enhanced nutrient acquisition from termite mounds appears to allow plants to tolerate herbivory and the reduced defense by a relatively ineffective ant partner. Our results underscore the importance of simultaneously examining top-down and bottom-up effects to understand those factors most important to plant reproductive success.

Species-Specific Seed Dispersal in an Obligate Ant-Plant Mutualism

Throughout lowland Amazonia, arboreal ants collect seeds of specific plants and cultivate them in nutrient-rich nests, forming diverse yet obligate and species-specific symbioses called Neotropical ant-gardens (AGs). The ants depend on their symbiotic plants for nest stability, and the plants depend on AGs for substrate and nutrients. Although the AGs are limited to specific participants, it is unknown at what stage specificity arises, and seed fate pathways in AG epiphytes are undocumented. Here we examine the specificity of the ant-seed interaction by comparing the ant community observed at general food baits to ants attracted to and removing seeds of the AG plant Peperomia macrostachya. We also compare seed removal rates under treatments that excluded vertebrates, arthropods, or both. In the bait study, only three of 70 ant species collected P. macrostachya seeds, and 84% of observed seed removal by ants was attributed to the AG ant Camponotus femoratus. In the exclusion experiment, arthropod exclusion significantly reduced seed removal rates, but vertebrate exclusion did not. We provide the most extensive empirical evidence of species specificity in the AG mutualism and begin to quantify factors that affect seed fate in order to understand conditions that favor its departure from the typical diffuse model of plant-animal mutualism.

Simplification of a coffee foliage-dwelling beetle community under low-shade management

Abstract Coffee agroforests may be structurally and floristically complex and may contain a significant fraction of species from biodiverse and threatened tropical montane forest biotas; hence, understanding the dynamics of tropical forest biodiversity in coffee agroecosystems has emerged as a centrally important area of tropical conservation biology research. We conducted a morphospecies analysis on foliage-dwelling beetles collected from coffee plants on four coffee farms in southern Chiapas, Mexico, to characterize variation in the abundance, species richness, and species composition of this mega-diverse taxon in relation to coffee cultivation system, spatio-temporal variation, and predator removal. We constructed thirty-two cages to exclude birds and bats on four farms, each enclosing 7–10 coffee plants and paired with an adjacent uncaged control plot, and then collected beetles from coffee foliage with D-Vac aspirators in each plot once every 3 months for one year. We classified the 2662 beetles collected into 293 morphospecies, representing 42 families of beetles. Extrapolation and interpolation analyses revealed a very high level of species richness, with no plateau and only a slight leveling trend observed in our species accumulation curves. We found that low-shade systems contain equal or higher beetle abundance, lower species richness, more highly homogenized species composition, and higher abundance of coffee berry borer pests on coffee foliage than do high-shade systems. We observed no effect of flying vertebrate exclusion on the coffee foliage beetle assemblage, but did find significant variation in abundance, species richness, and species composition of coffee foliage beetles across seasons and study sites. The increased beetle biodiversity of high-shade coffee cultivation systems has important implications both for the preservation of native biodiversity in coffee growing regions and for the control of agricultural pests such as the coffee berry borer.

Seed Dynamics of Early and Late Successional Tree Species in Tropical Abandoned Pastures: Seed Burial as a Way of Evading Predation

Abstract We explored different treatments to enhance the probability of sowed seeds of two early successional (ES, Cecropia obtusifolia and Ochroma pyramidale) and two late successional (LS, Brosimum costaricanum and Dialium guianense) species to escape predation and germinate in abandoned cattle‐raising pasture fields in Southeastern Mexico. ES species were sown in groups of 50 seeds under three treatments: invertebrate exclusion, burial, and exposition to seedeaters. LS species were sown in groups of 10 seeds under three treatments: vertebrate exclusion, burial, and exposition to seedeaters. We registered seed predation and germination 2, 4, 8, 16, 32, and 64 days after the initial sowing. Overall, ES showed higher predation rates (mean ± SE = 0.45 ± 0.07 seed seed−1 day−1; n = 3) than LS species (0.09 ± 0.02 seed seed−1 day−1). Cecropia obtusifolia was completely predated in all treatments after 8 days. Burial and exclusion treatments reduced final predation in circa 6% for O. pyramidale, relative to that of exposed seeds (85% after 8 days); most germination occurred in buried seeds (3.7%). In B. costaricanum, burial enabled germination by 10%; exposed and excluded seeds were removed 100%. Dialium guianense showed 12% germination in buried seeds and circa 20% of the seeds were not removed after 64 days. Direct sowing would be a recommended rainforest restoration practice for species with relatively large seeds if deposited in groups and buried. Studies which address variation across numerous sites are necessary in order to generate more consistent seed predation patterns and rainforest restoration principles in tropical pastures.

Pollination Systems of Colchicum (Colchicaceae) in Southern Africa: Evidence for Rodent Pollination

Plants adapted for pollination by rodents tend to exhibit a distinct floral syndrome that includes dull coloured and geoflorous inflorescences and nocturnal anthesis and nectar production. On the basis of their floral traits, it was predicted that two African Colchicum species (C. scabromarginatum and C. coloratum) are rodent-pollinated. Field studies were carried out in the semi-arid Succulent Karoo region of South Africa. Live trapping of rodents was conducted and pollen loads on the rodents were quantified. The daily periodicity of nectar production was determined. Selective exclusion and controlled pollination experiments were also conducted. Live-trapped rodents were found to carry large amounts of Colchicum pollen on the fur of their snouts, and in their faeces. Birds were occasional pollinators of flowers of C. coloratum. During the evening, nectar volume and concentration increased for both species. When vertebrates were excluded from C. scabromarginatum and C. coloratum plants, there was a significant decrease in seed set compared with open control plants. By contrast, vertebrate exclusion did not significantly affect seed production of a congener, C. hantamense, which has floral traits associated with insect pollination. Breeding system experiments revealed that both C. scabromarginatum and C. coloratum require pollinators for seed production. Colchicum scabromarginatum is strictly self-incompatible, whereas C. coloratum is partially self-compatible. Pollination by rodents occurs in two African Colchicum species. C. scabromarginatum appears to depend exclusively on rodents for seed production, while birds and autonomous selfing may contribute to seed production in C. coloratum. These are the first records of rodent pollination in the Colchicaceae.

An Atlas Improves Interobserver Agreement Regarding Application of the ISCD Vertebral Body Exclusion Criteria

Coexisting conditions such as osteoarthritis and compression fracture may spuriously elevate the dual-energy X-ray absorptiometry (DXA)-measured lumbar spine bone mass. To improve the diagnostic utility of lumbar spine DXA to diagnose osteoporosis, the International Society for Clinical Densitometry (ISCD) suggests excluding vertebrae affected by focal structural anomalies or unusual T-score discrepancies. However, we previously demonstrated only moderate agreement between physicians regarding vertebral body exclusion. We hypothesized that an atlas containing examples of vertebrae to exclude would improve interobserver agreement. Subsequently, we developed an interactive web-based atlas of lumbar spine DXA images with options to exclude vertebrae and compare one's answers to those derived by group consensus. Before and after review of the atlas, 5 ISCD-certified physicians applied the exclusion criteria to 90 DXA scans, recording the indications for vertebral exclusion on a standardized worksheet. After development and review of the atlas, interobserver agreement regarding vertebral body exclusion improved significantly ( p < 0.0001). We plotted the deviation of each physician's reported T-score vs the mean T-score for each of 90 scans, and demonstrated that the scatter from the mean is decreased after atlas review. Furthermore, correlations in T-score improved in 7 of 10 physician pairs after atlas review. We conclude that an interactive atlas promotes uniform lumbar spine DXA interpretation.

Exclusion of Focal Vertebral Artifacts From Spine Bone Densitometry and Fracture Prediction: A Comparison of Expert Physicians, Three Computer Algorithms, and the Minimum Vertebra

Expert physicians and automated methods for the exclusion of vertebral levels in DXA scans containing focal artifacts were compared. All methods of vertebral exclusion led to a small improvement in fracture prediction. Computer algorithms performed at least as well as physicians. Lumbar spine DXA is often confounded by focal artifacts. Clinical rules and automated methods for vertebral exclusion have been proposed, but their concordance, effect on diagnosis, and fracture prediction is unknown. We analyzed clinical DXA scans of the lumbar spine (20,478 women and 1534 men) performed from 1998 to 2002 (Province of Manitoba, Canada). Longitudinal health service records were assessed for the presence of nontrauma fracture codes after BMD testing. The effect of vertebral exclusions by expert physicians and several automated methods on diagnosis and prediction of incident fractures was compared. Vertebral exclusions were reported by physicians in over one quarter of the scans (31% of women and 29% of men). All methods of vertebral exclusion significantly decreased the mean spine T-score and increased the proportion of women designated as osteoporotic. kappa values and ROC area under the curve (AUC) for physician-computer agreement in the identification of abnormal scans indicated fair to moderate agreement in both women and men. Compared with no vertebral exclusions, a small increase in the hazard ratio and AUC for spine fracture and osteoporotic fracture prediction was seen after physician and computer exclusions. Compared with physician exclusions, AUC for prediction of osteoporotic fractures in men increased significantly with one computer algorithm (p = 0.004). The minimum vertebral T-score enhanced fracture prediction compared with no exclusions but approximately doubled the prevalence of osteoporotic categorization. We observed fair to moderate agreement between the physician and computer methods for vertebral level exclusion. All methods of vertebral exclusion led to a small improvement in fracture prediction using the lumbar spine measurement. The automated algorithms performed at least as well as physicians when fractures were used as the endpoint.

Developing an atlas of focal structural defects (FSD) to improve inter-observer agreement regarding the application of ISCD vertebral body exclusion criteria

Developing an atlas of focal structural defects (FSD) to improve inter-observer agreement regarding the application of ISCD vertebral body exclusion criteria

Interobserver Reproducibility of Criteria for Vertebral Body Exclusion

We studied reproducibility of the ISCD vertebral exclusion criteria among four interpreters. Surprisingly, agreement among interpreters was only moderate, because of differences in threshold for diagnosing focal structural defects and choice of which vertebra among a pair discordant for T-score, area, or BMC to exclude. Our results suggest that reproducibility may be improved by specifically addressing the sources of interobserver disagreement. Although DXA is widely used to measure vertebral BMD, its interpretation is subject to multiple confounders including osteoarthritis, aortic calcification, and scoliosis. In an attempt to standardize interpretation and minimize the impact of artifacts, the International Society for Clinical Densitometry (ISCD) established criteria for vertebral exclusion, including the presence of a focal structural defect (FSD), discrepancy of >1 SD in T-score between adjacent vertebrae, and a lack of increase in BMC or area from L1 to L4. Whereas the efforts of the ISCD represent an important advance in BMD interpretation, the interobserver reproducibility with application of these criteria is unknown. We hypothesized that there would be substantial agreement among four interpreters regarding application of the exclusion criteria and the final lumbar spine T-score. Each interpreter read a set of 200 lumbar DXA scans obtained on male veterans, applying the ISCD vertebral body exclusion criteria. Surprisingly, agreement among interpreters was only moderate. Differences in interpretation resulted from differing thresholds for recognition of FSD and the choice of excluding the upper or lower vertebral body for the criteria requiring comparison between adjacent vertebrae. Despite their apparent simplicity, the ISCD vertebral exclusion criteria are difficult to apply consistently. In principle, appropriate refinement of the exclusion criteria may significantly improve interobserver agreement.

Can the Argentine ant (Linepithema humile Mayr) replace native ants in myrmecochory?

We analyse the influence of the Argentine ant (Linepithema humile Mayr) on the seed dispersal process of the myrmecochorous plants Euphorbia characias, E. biumbellata, Genista linifolia, G. triflora, G. monspessulana and Sarothamnus arboreus. The observations were made in two study plots of Mediterranean cork-oak secondary forest (invaded and non-invaded by L. humile). The presence of L. humile implies the displacement of all native ant species that disperse seeds. Seed transports in the non-invaded zone were carried out by eight ant species. In the invaded zone, L. humile workers removed and transported seeds to the nest. In vertebrate exclusion trials, we observed the same level of seed removal in the invaded and non-invaded zones. Two findings could explain this result. Although mean time to seed localization was higher for native ants (431.7 s) than that for L. humile (150.5 s), the mean proportion of seeds transported after being detected was higher (50.1%) in non-invaded than in invaded (16.8%) zones. The proportion of seeds removed and transported into an ant nest after an ant-seed interaction had dramatically reduced from non-invaded (41.9%) to invaded (7.4%) zones. The levels of seed dispersal by ants found prior to invasion are unlikely to be maintained in invaded zones. However, total replacement of seed dispersal function is possible if contact iteration finally offers similar levels or quantities of seeds reaching the nests. The results obtained confirm that the Argentine ant invasion may affect myrmecochory dramatically in the Mediterranean biome.

Mixed mating in Banksia media

Differential exclusion of vertebrates and invertebrates from the inflorescences of Banksia media R.Br. on the south coast of Western Australia showed the species to be partially self-compatible. Access by invertebrates increased fruit set and additional access by vertebrates resulted in even greater fruit set. Honeyeater birds and marsupial nectarivores were abundant and widespread in the study area and most carried the pollen of Banksia media while it flowered. However, although B. media had the floral characteristics attributed to vertebrate pollination, self-pollination and pollination by insects clearly also play major roles in seed production. Banksia media regenerates solely from seed released after fire and we suggest that its mixed mating strategy is a compromise between inbreeding depression and risk of elimination from areas prone to occasional fires.