Lianas have a greater competitive effect than trees of similar biomass on tropical canopy trees

Lianas (woody vines) reduce growth and survival of host trees in both temperate and tropical forests; however, the relative strength of liana‐tree competition in comparison to tree‐tree competition remains unexplored. When controlling for biomass, lianas may have greater competitive effects than trees because the unique morphology of lianas allows them to reach the forest canopy at relatively small stem diameters and deploy a substantial crown above their host. We tested the hypothesis that lianas have a greater negative effect on canopy trees than do trees of similar biomass with a liana‐ and tree sapling‐cutting experiment in a seasonal tropical moist forest in Panama. The response of canopy trees to the cutting treatments was characterized as the change in their daily water use by measuring their sap velocity before and after cutting. We compared the responses of canopy trees around which a similar biomass of either lianas or tree saplings had been cut to control trees with no cutting. Liana cutting increased canopy‐tree sap velocity by ∼8% from before to after cutting relative to control trees during the dry season. In contrast, canopy‐tree sap velocity did not respond to tree cutting, probably because trees with biomass similar to lianas were confined to the forest understory. We observed a similar pattern of sap velocity changes during the wet season, but treatment differences were not significant. Our results demonstrate that release from liana competition, but not tree competition, resulted in increased water transport in canopy trees, and suggests that relative to their biomass, lianas have greater competitive effects on canopy tree performance than do competing trees

Unique Competitive Effects of Lianas and Trees in a Tropical Forest Understory

Lianas are an important component of tropical forests, contributing up to 25 % of the woody stems and 35 % of woody species diversity. Lianas invest less in structural support but more in leaves compared to trees of similar biomass. These physiological and morphological differences suggest that lianas may interact with neighboring plants in ways that are different from similarly sized trees. However, the vast majority of past liana competition studies have failed to identify the unique competitive effects of lianas by controlling for the amount of biomass removed. We assessed liana competition in the forest understory over the course of 3 years by removing liana biomass and an equal amount of tree biomass in 40 plots at 10 sites in a secondary tropical moist forest in central Panama. We found that growth of understory trees and lianas, as well as planted seedlings, was limited due to competitive effects from both lianas and trees, though the competitive impacts varied by species, season, and size of neighbors. The removal of trees resulted in greater survival of planted seedlings compared to the removal of lianas, apparently related to a greater release from competition for light. In contrast, lianas had a species-specific negative effect on drought-tolerant Dipteryx oleifera seedlings during the dry season, potentially due to competition for water. We conclude that, at local scales, lianas and trees have unique and differential effects on understory dynamics, with lianas potentially competing more strongly during the dry season, and trees competing more strongly for light

Applications of Sensory Ecology for Wildlife Damage Management

Human-wildlife conflicts typically involve fundamental processes associated with the feeding behavior and/or the spatial behavior of wildlife. Thus, most human-wildlife conflicts arise from wildlife consuming products and/or wildlife occupying places valued by humans. For mammals, taste is the most important sensory cue for selecting nutrients and avoiding toxins. Most birds use both flavor (i.e. taste, odor, texture) and visual cues for their food selection process. We previously learned that an ultraviolet visual cue can enhance the repellency of an anthraquinone-based repellent for blackbirds, starlings, Canada geese and wild turkeys. Although the ultraviolet cue is not itself aversive, novel repellent formulations including ultraviolet cues have provided repellent efficacy at reduced concentrations of the repellent active ingredient. Ultraviolet repellent formulations are currently being developed for the protection of ripening agricultural crops from bird depredation. With regard to spatial behavior, exteroceptive sensory cues (e.g. visual, auditory, tactile cues) are reliably used for patch selection. We suggest that sensory cues and their paired consequences can be exploited for the development and application of effective strategies for wildlife damage management

A molecular analysis to assess codling moth \u3ci\u3eCydia pomonella\u3c/i\u3e L. (Lepidoptera: Tortricidae) predation by orchard birds

The codling moth Cydia pomonella L. (Lepidoptera: Tortricidae) is a major economic pest in organic apple orchards. Observational methods, prey removal experiments and correlative experiments with exclosures or nest boxes have demonstrated that birds contribute to the removal of this insect pest. However, the majority of research conducted in the last several decades has taken place outside of the United States and methods for studying biological pest control have advanced dramatically and now include molecular techniques. We conducted a proof-of-concept study to test a DNA-based approach to detect C. pomonella prey in the diets of birds occupying organic apple orchards. We tested published Tortricidae primers, polymerase chain reaction (PCR) and sequencing for detection of C. pomonella in avian feces. We also tested the quality of DNA isolated and purified from fecal samples using two DNA extraction kits. Finally, we field-tested this tool to identify the presence or absence of C. pomonella in the laboratory and from field samples. C. pomonella DNA was amplified in less than 1% of field samples and was successfully sequenced in 0.5%. A single species, the brown-headed cowbird Molothrus ater (Boddaert), had fecal samples positive for C. pomonella DNA. While our results do not provide evidence that birds play a strong role in the control of C. pomonella in western Colorado organic apple orchards, the approach we present is a new tool for understanding bird-mediated ecosystem services, avian feeding ecology, and supporting management decisions for sustainable agricultural practices and farmland biodiversity

Complex facilitation and competition in a temperate grassland: loss of plant diversity and elevated CO\u3csub\u3e2\u3c/sub\u3e have divergent and opposite effects on oak establishment

Encroachment of woody vegetation into grasslands is a widespread phenomenon that alters plant community composition and ecosystem function. Woody encroachment is often the result of fire suppression, but it may also be related to changes in resource availability associated with global environmental change. We tested the relative strength of three important global change factors (CO2 enrichment, nitrogen deposition, and loss of herbaceous plant diversity) on the first 3 years of bur oak (Quercus macrocarpa) seedling performance in a field experiment in central Minnesota, USA. We found that loss of plant diversity decreased initial oak survival but increased overall oak growth. Conversely, elevated CO2 increased initial oak seedling survival and reduced overall growth, especially at low levels of diversity. Nitrogen deposition surprisingly had no net effect on survival or growth. The magnitude of these effects indicates that long-term woody encroachment trends may be most strongly associated with those few individuals that survive, but grow much larger in lower diversity patches. Further, while the CO2 results and the species richness results appear to describe opposing trends, this is due only to the fact that the natural drivers are moving in opposite directions (decreasing species richness and increasing CO2). Interestingly, the mechanisms that underlie both patterns are very similar, increased CO2 and increased species richness both increase herbaceous biomass which (1) increases belowground competition for resources and (2) increases facilitation of early plant survival under a more diverse plant canopy; in other words, both competition and facilitation help determine community composition in these grasslands

Negative plant–soil feedback predicts tree-species relative abundance in a tropical forest

The accumulation of species-specific enemies around adults is hypothesized to maintain plant diversity by limiting the recruitment of conspecific seedlings relative to heterospecific seedlings1,2,3,4,5,6. Although previous studies in forested ecosystems have documented patterns consistent with the process of negative feedback7,8,9,10,11,12,13,14,15,16, these studies are unable to address which classes of enemies (for example, pathogens, invertebrates, mammals) exhibit species-specific effects strong enough to generate negative feedback17, and whether negative feedback at the level of the individual tree is sufficient to influence community-wide forest composition. Here we use fully reciprocal shade-house and field experiments to test whether the performance of conspecific tree seedlings (relative to heterospecific seedlings) is reduced when grown in the presence of enemies associated with adult trees. Both experiments provide strong evidence for negative plant–soil feedback mediated by soil biota. In contrast, above-ground enemies (mammals, foliar herbivores and foliar pathogens) contributed little to negative feedback observed in the field. In both experiments, we found that tree species that showed stronger negative feedback were less common as adults in the forest community, indicating that susceptibility to soil biota may determine species relative abundance in these tropical forests. Finally, our simulation models confirm that the strength of local negative feedback that we measured is sufficient to produce the observed community-wide patterns in tree-species relative abundance. Our findings indicate that plant–soil feedback is an important mechanism that can maintain species diversity and explain patterns of tree-species relative abundance in tropical forests

Resource‐based habitat associations in a neotropical liana community

Summary 1. Lianas are a conspicuous element of many tropical forests, accounting for up to 40% of woody stem density and 20% of species richness in seasonal forests. However, lianas have seldom been surveyed at sufficiently large spatial scales to allow an assessment of the importance of habitat variables in structuring liana communities. 2. We compare the association patterns of 82 liana species and an equivalent sample of tree species on the 50 ha Forest Dynamics Project plot on Barro Colorado Island, Panama, with topographic habitat variables (high and low plateau, slope, swamp and streamside), and thirteen mapped soil chemical variables. In addition, we test for liana species associations with canopy disturbance using a canopy height map of the plot generated using light detection and ranging. 3. For all liana species combined, densities differed among topographic habitat types in the plot, with significantly higher densities on the seasonally drier lower plateau habitat (1044 individuals ha−1) than the moister slope habitat (729 individuals ha−1). Lianas were also significantly more abundant than expected in areas with low canopy height. 4. The proportion of liana species associated with one or more topographic habitat variables (44%) was significantly lower than that for trees (66%). Similarly, liana species were significantly less frequently associated with PC axes derived from soil chemical variables (21%) than trees (52%). The majority of liana species (63%) were significantly associated with areas of the plot with low canopy height reflecting an affinity for treefall gaps. 5. Synthesis. The habitat associations detected here suggest that liana density is associated primarily with canopy disturbance, and to a lesser extent with topography and soil chemistry. Relative to trees, few liana species were associated with local variation in topography and soil chemistry, suggesting that nutrient availability exerts only weak effects on liana community composition compared to trees. Results from this study support the contention that increases in forest disturbance rates are a driver of recently observed increases in liana abundance and biomass in neotropical forests

Globally, plant-soil feedbacks are weak predictors of plant abundance

Plant-soil feedbacks (PSFs) have been shown to strongly affect plant performance under controlled conditions, and PSFs are thought to have far reaching consequences for plant population dynamics and the structuring of plant communities. However, thus far the relationship between PSF and plant species abundance in the field is not consistent. Here, we synthesize PSF experiments from tropical forests to semiarid grasslands, and test for a positive relationship between plant abundance in the field and PSFs estimated from controlled bioassays. We meta-analyzed results from 22 PSF experiments and found an overall positive correlation (0.12 <= r over bar <= 0.32) between plant abundance in the field and PSFs across plant functional types (herbaceous and woody plants) but also variation by plant functional type. Thus, our analysis provides quantitative support that plant abundance has a general albeit weak positive relationship with PSFs across ecosystems. Overall, our results suggest that harmful soil biota tend to accumulate around and disproportionately impact species that are rare. However, data for the herbaceous species, which are most common in the literature, had no significant abundance-PSFs relationship. Therefore, we conclude that further work is needed within and across biomes, succession stages and plant types, both under controlled and field conditions, while separating PSF effects from other drivers (e.g., herbivory, competition, disturbance) of plant abundance to tease apart the role of soil biota in causing patterns of plant rarity versus commonness