Latitudinal decrease in folivory within Nothofagus pumilio forests: dual effect of climate on insect density and leaf traits?

Aim The strength of consumer–plant interactions may decrease with latitude. Our objectives were to assess the spatial variation in folivory on Nothofagus pumilio and understand the influence of climate on folivory patterns as mediated by changes in folivore density and leaf traits. Location Nothofagus pumilio forests, between 38 and 55°S (Argentina). Methods We studied the correlation of leaf damage with latitude on data from 47 sampling sites, and evaluated spatial patterns of autocorrelation on latitudinally detrended data with a principal coordinates of neighbour matrices method. Path analysis was used to test the association of temperature and precipitation with leaf damage, mediated by folivore density and leaf traits. We evaluated the adequacy of this ecological model by examining the spatial pattern of autocorrelation in the residuals, and combined spatial and environmental predictors of leaf damage into partial regression. Results Leaf damage decreased with latitude, which was the only significant spatial predictor. The latitudinal decrease in temperature and precipitation was correlated with a decrease in the density of folivores and leaf size, and diminished leaf damage. Our ecological model adequately explained the spatial autocorrelation in the data: 44% of the variation in leaf damage was explained by the latitudinally structured component of the environment, whereas local environmental effects accounted for another 22%. Main conclusions We conclude that N. pumilio forests show consistent latitudinal patterns of variation in folivory, folivore density and leaf traits. Our study suggests that the latitudinal variation in folivory rates is partly driven by the influence of climate on both plants and herbivores. This warns us about the potential susceptibility of folivory rates to climate warming. We emphasize the value of large‐scale analyses as complementary to local experimental approaches to understanding the regulation of herbivory.     

Variable strength of top‐down effects in Nothofagus forests: bird predation and insect herbivory during an ENSO event

Abstract Predators are thought to play a key role in controlling herbivory, thus having positive indirect effects on plants. However, evidence for terrestrial trophic cascades is still fragmentary, perhaps due to variation in top‐down forces created by environmental heterogeneity. We examined the magnitude of predation effects on foliar damage by chewing insects and mean leaf size, by excluding birds from saplings in ‘dry’ and ‘wet’Nothofagus pumilio forests in the northern Patagonian Andes, Argentina. The experiment lasted 2 years encompassing a severe drought during the La Niña phase of a strong El Niño/Southern Oscillation event, which was followed by unusually high background folivory levels. Insect damage was consistently higher in wet than in dry forest saplings. In the drought year (1999), bird exclusion increased folivory rates in both forests but did not affect tree leaf size. In the ensuing season (2000), leaf damage was generally twice as high as in the drought year. As a result, bird exclusion not only increased the extent of folivory but also significantly decreased sapling leaf size. The latter effect was stronger in the wet forest, suggesting compensation of leaf area loss by dry forest saplings. Overall, the magnitude of predator indirect effects depended on the response variable measured. Insectivorous birds were more effective at reducing folivory than at facilitating leaf area growth. Our results indicate that bird‐initiated trophic cascades protect N. pumilio saplings from insect damage even during years with above‐normal herbivory, and also support the view that large‐scale climatic events influence the strength of trophic cascades.     

Nutrient supply and bird predation additively control insect herbivory and tree growth in two contrasting forest habitats

It has been suggested that bottom–up and top–down forces interactively control food web dynamics. While top–down effects would increase with resource availability to plants, bottom–up effects would be stronger under low predator abundance. These predictions, however, have rarely been tested at contrasting sites while keeping the dominant plant species unchanged. Furthermore, few studies have factorially manipulated both types of forces in forest communities. For two years, we evaluated the effects of fertiliser (NPK) addition and bird exclusion on tree growth, leaf traits, insect abundance, and folivory rates in a dry/warm and a wet/cold Nothofagus pumilio forest in Patagonia, Argentina. Overall, we found no interaction between nutrient supply and bird predation, although the strength of bottom–up and top–down forces differed markedly between forest sites. Treatment effects were generally weak in the wet forest, where tree growth rates and insect herbivory were low relative to the dry forest. In the dry forest, fertilisation increased sapling growth, insect abundance and folivory, whereas bird exclusion increased leaf damage and reduced tree growth. In the wet forest, fertilisation enhanced leaf nutrient contents and folivore abundance but not sapling growth, while bird exclusion had little impact on insects or trees. These results imply that factors other than nutrients and birds were important in controlling tree growth and folivore activity in the wet forest. While treatment effect sizes varied widely among feeding guilds, in general, nutrient effects on folivores were stronger than predator effects. We conclude that, within the time‐frame of this study, tree growth and herbivory were additively affected by soil nutrients and predator presence, as bird exclusion effects did not change with elevated folivore activity on fertilised trees. We also show that both top–down and bottom–up cascades were weaker in a forest site characterised by slow‐growing juvenile trees subjected to low folivore pressure.     

Insect herbivory and herbivores of Ficus species along a rain forest elevational gradient in Papua New Guinea

Classic research on elevational gradients in plant–herbivore interactions holds that insect herbivore pressure is stronger under warmer climates of low elevations. However, recent work has questioned this paradigm, arguing that it oversimplifies the ecological complexity in which plant–insect herbivore interactions are embedded. Knowledge of antagonistic networks of plants and herbivores is however crucial for understanding the mechanisms that govern ecosystem functioning. We examined herbivore damage and insect herbivores of eight species of genus Ficus (105 saplings) and plant constitutive defensive traits of two of these species, along a rain forest elevational gradient of Mt. Wilhelm (200–2,700 m a.s.l.), in tropical Papua New Guinea. We report overall herbivore damage 2.4% of leaf area, ranging from 0.03% in Ficus endochaete at 1,700 m a.s.l. to 6.1% in F. hombroniana at 700 m a.s.l. Herbivore damage and herbivore abundances varied significantly with elevation, as well as among the tree species, and between the wet and dry season. Community-wide herbivore damage followed a hump-shaped pattern with the peak between 700 and 1,200 m a.s.l. and this pattern corresponded with abundance of herbivores. For two tree species surveyed in detail, we observed decreasing and hump-shaped patterns in herbivory, in general matching the trends found in the set of plant defenses measured here. Our results imply that vegetation growing at mid-elevations of the elevational gradient, that is at the climatically most favorable elevations where water is abundant, and temperatures still relatively warm, suffers the maximum amount of herbivorous damage which changes seasonally, reflecting the water availability.     

Interannual changes in folivory and bird insectivory along a natural productivity gradient in northern Patagonian forests

Trophic regulation models suggest that the magnitude of herbivory and predation (top-down forces) should vary predictably with habitat productivity. Theory also indicates that temporal abiotic variation and within-trophic level heterogeneity both affect trophic dynamics, but few studies addressed how these factors interact over broad-scale environmental gradients. Here we document herbivory from leaf-feeding insects along a natural rainfall/productivity gradient in Nothofagus pumilio forests of northern Patagonia, Argentina, and evaluate the impact of insectivorous birds on foliar damage experienced by tree saplings at each end of the gradient. The study ran over three years (1997–2000) comprising a severe drought (1998–1999), which allowed us to test how climatic events alter top-down forces. Foliar damage tended to increase towards the xeric, least productive forests. However, we found a predictable change of insect guild prevalence across the forest gradient. Leaf miners accounted for the greater damage recorded in xeric sites, whereas leaf chewers dominated in the more humid and productive forests. Interannual folivory patterns depended strongly on the feeding guild and forest site. Whereas leaf-miner damage decreased during the drought in xeric sites, chewer damage increased after the drought in the wettest site. Excluding birds did not affect leaf damage from miners, but generally increased chewer herbivory on hydric and xeric forest saplings. Indirect effects elicited by bird exclusion became most significant after the drought, when total folivory levels were higher. Thus, interannual abiotic heterogeneity markedly influenced the amount of folivory and strength of top-down control observed across the forest gradient. Moreover, our results suggest that spatial turnovers between major feeding guilds may need be considered to predict the dynamics of insect herbivory along environmental gradients.     

Ontogenetic and temporal variations in herbivory and defense of Handroanthus spongiosus (Bignoniaceae) in a Brazilian tropical dry forest

We compared the richness and abundance of free-feeding herbivore insects (sap-sucking and leaf-chewing), leaf herbivory damage, leaf toughness and total phenolic content between two ontogenetic stages (juvenile and reproductive) of Handroanthus spongiosus (Rizzini) S. O. Grose (Bignoniaceae) throughout the rainy season in a Brazilian seasonally dry tropical forest. Twenty marked individuals of H. spongiosus were sampled per ontogenetic stage in each period of the rainy season (beginning, middle, and end). Herbivore richness and abundance did not differ between ontogenetic stages, but higher percentage of leaf damage, higher concentration of phenolic compounds, and lower leaf toughness were observed for juvenile individuals. The greatest morphospecies abundance was found at the beginning of the rainy season, but folivory increment was higher at the end, despite the fact that leaf toughness and total phenolic content increased in the same period. No significant relationships between leaf damage and both total phenolic content and leaf toughness were observed. These results suggest that insect richness and abundance do not track changes in foliage quality throughout plant ontogeny, but their decrease along rainy season confirms what was predicted for tropical dry forests. The general trends described in the current study corroborate those described in the literature about herbivores and plant ontogeny. However, the lack of relationship between herbivore damage and the two plant attributes considered here indicates that the analyses of multiple defensive traits (the defense syndrome) must be more enlightening to determine the mechanisms driving temporal and spatial patterns of herbivore attack.     

Contrasting climate influences on Nothofagus pumilio establishment along elevational gradients

Predicted warmer temperatures and more frequent extreme climatic events in the southern Andes may affect the dynamics of the Patagonian forests. These environmental changes may differentially alter the probability of Nothofagus pumilio establishment across its altitudinal range of distribution. We monitored fruit fall, seedling emergence and survival at altitudinal distribution range of N. pumilio forests in Santa Cruz (49°22′ S—72°56′ W), Argentina. Fruit fall, seedling emergence and survival were tested in relation to drought, based on the SPEI (Standardized Precipitation Evapotranspiration Index), interacting with elevation. Fruit fall was consistently higher at low elevation and the abundance of fruits was not affected by drought intensity. Density of new-born seedlings was?~?9 to 24 times lower at low- than at high-elevation plots in our first observations (2014 and 2016), characterized by warm-dry climatic conditions in spring-early summers. In contrast, seedling abundance was?~?1.5 times larger at low elevations during relatively cold-wet growing seasons. Survival probability was explained by the interaction between SPEI and elevation. At low elevation and in dry periods, survival probability was lower (CI 54–72%) than in wet periods (CI 68–84%) but at high elevation similar survival was registered even with positive or negative SPEI values. Our results show interacting effects of elevation and drought on tree establishment at the elevation limits, with positive and negative drought effects at high and low elevations, respectively. Predicted increase of extreme drought events during the XXI century could be detrimental for N. pumilio establishment at dry, low-elevation forests.

     

Ecological interactions among insect herbivores,ants and the host plant Baccharis dracunculifolia in a Brazilian mountain ecosystem

Insect–plant interactions occur in several ways and have considerable environmental and ecological importance. Many feeding strategies have evolved among herbivorous insects, with host–herbivore systems likely being influenced by trophobionts with ants. We investigated how these interactions vary across elevation gradients by evaluating the structure of the herbivorous insect community and ants associated with Baccharis dracunculifolia at three distinct elevations (800, 1100, and 1400 m a.s.l.) on a mountain in southeastern Brazil. Moreover, we evaluated the diversity and specialisation of interactions between herbivores and host plants along the elevational gradient. We sampled herbivores and ants on 60 plants at each elevation (totalling 180 plant individuals). Herbivore species composition differed among elevations, as did interaction diversity and specialisation. Richness and abundance of chewing insects increased with elevation, while β‐diversity among patches of the host plant was higher at the lowest elevation, probably due to the patchy occurrence of B. dracunculifolia. Richness and abundance of sap‐sucking insects were higher at the intermediate elevation, possibly due to local environmental conditions. We observed a positive relationship between ant and herbivore trophobiont richness on B. dracunculifolia. We found that interactions were more specialised and less diverse at higher elevations compared to the lowest elevation. Changes in vegetation and environmental variables shaped species distributions and their ecological interactions along the elevation gradient. Our study demonstrates that increased elevation changes the structure and patterns of interactions of the herbivore insect guilds associated with the host plant B. dracunculifolia. Ant effects depend on the context, the environment, and the species of ants involved, and are essential for the presence of insect trophobionts.     

Morphological and phenological differences in Nothofagus pumilio from contrasting elevations: Evidence from a common garden

Abstract We tested the hypothesis that contrasting elevations select distinct growth patterns and vegetative phenology in Nothofagus pumilio, a winter deciduous tree that dominates mountain forests of Patagonia. Analysis of saplings maintained under common‐garden conditions for 4 years showed a significant decrease in shoot annual growth, leaf size, and a delay in bud‐break, and leaf expansion with increased elevation of their site of origin. Rapid gain in height seems to be advantageous at low elevation in such light‐demanding species. Lower stature high‐elevation plants have wider branching angles and greater branching ratios (number of branches/number of internodes) than low‐elevation plants. Compact growth at high elevation may be related to strong winds and irradiance. Plants from different elevations had distinct growth patterns during the common‐garden experiment. This could be of importance in Mediterranean‐climate areas characterized by highly unpredictable precipitation regimes. Also, liberation of growth‐suppressed seedlings may follow different environmental signals in low‐ and high‐habitats, which might explain such time‐dependent responses to optimal conditions under cultivation. While these greenhouse‐grown N. pumilio saplings showed heritable differences in plant architectural traits and leafing phenology, it was not clear how the genotypes characteristic of particular elevations would respond to longer growing seasons such as those predicted under global warming.     

Effect of elevation on the insect herbivory of Mongolian oaks in the high mountains of southern South Korea

Elevation is strongly associated with the diversity and ecology of plants and animals. We explored how elevation affects herbivores on one of the major cool-temperate trees, Quercus mongolica, in southern South Korea. The feeding activities of insect herbivores were measured through insect-feeding damage on leaves. Of 78 types of insect-feeding damage that were observed from Jirisan Mountain (Mount.) and Hallasan Mount. in Korea, 61.6% was associated with externally feeding insects. The sum of feeding damages per leaf was significantly higher on Jirisan Mount. than on Hallasan Mount., and higher at higher elevation in both mountains. Two feeding guilds, externally feeding, and piercing and sucking were strongly related with elevation, but the relationship was opposite depending on feeding guild. Leaf damage by the internal feeding guild showed no effect of elevation at the two mountains. These study results showed that insect herbivory responds to elevational differences in temperate forests, and that such response can vary among feeding guilds.     

Seed dispersal of a fleshy-fruited invasive shrub is affected by changes in the frugivorous bird assemblage along an elevational gradient

Seed dispersal by birds constitutes an essential mechanism for ornithochorous exotic plants to successfully invade a new system. New biotic associations with native birds might facilitate the upward spread of exotic plants from the foothills into the high mountains. However, environmental changes associated with elevation are known to drive changes in bird assemblages, and it is not clear how elevation changes impact the seed dispersal service of ornithochorous invaders. We evaluated changes in frugivorous bird assemblages of one of the exotic shrubs (Cotoneaster franchetii, Rosaceae) with the broadest elevation range among woody invaders in the Córdoba Mountains (Argentina). We quantified frugivory interactions (including absolute and proportional fruit consumption by seed dispersers, pulp consumers, and seed predators) using 4-h observations of focal C. franchetii shrubs distributed across low-elevation, mid-elevation, and high-elevation sites (700, 1100, and 1800 m a.s.l., respectively; 15 individuals per elevational band and one site per elevation). Seed disperser richness was highest at the low- and mid-elevation sites (three species vs. one at the high-elevation site), but proportional and absolute fruit consumption of C. franchetii was highest at the high-elevation site (39.1%, 88 seeds at high-elevation and 7.7%, 20 seeds at low-elevation). The Chiguanco Thrush (Turdus chiguanco, Turdidae) was the only seed disperser species found at the highest elevation site. Fruit consumption by seed dispersers was positively related to their abundance and elevation. In a high mountain system, a single abundant generalist seed disperser, rather than a high richness of seed disperser species, can uphold an effective dispersal service for an invasive ornithochorous shrub. This pattern may facilitate the spread of such plants across higher elevational ranges, thereby promoting the invasion of other exotic ornithochorous plants into upper elevations.     

Seasonal patterns of herbivory,leaf traits and productivity consumption in dry and wet Patagonian forests

1. Endemic herbivory can influence forest ecosystem function, but how annual productivity consumption relates to seasonal resource utilisation by folivore guilds remains poorly understood. 2. Monthly changes in leaf damage and foliage traits were monitored in ‘dry’ and ‘wet’Nothofagus pumilio (Fagales: Nothofagaceae) deciduous forests in northern Patagonia, Argentina. Herbivore‐induced leaf abscission was assessed and foliar productivity consumption was measured in the canopy and in litterfall harvests. 3. Seasonal damage ranged from 8% to 32% in dry forest, but remained below 5% in wet forest although foliar quality was higher in the latter. In dry forest, dominant guilds were temporally separated; leaf miners consumed younger foliage in spring to early summer, whereas leaf tiers prevailed in late summer to autumn. In wet forest, damage created by external chewers was concentrated in early summer. 4. Insect damage induced premature leaf abscission, especially in dry forest. Although foliar production in wet forest doubled that in dry forest, the percentage of productivity lost to folivores was higher in dry (14–20%) than in wet (1.2–1.8%) forest. 5. The overall greater impact of herbivory in dry forest canopies countered the expectation that consumption would increase with plant productivity and nutritional quality. Lower temperatures and a shorter growing season are likely to constrain folivory in wet forest stands.     

Indirect effects of deer on insect pests and soybean plants

1. White-tailed deer (Odocoileus virginianus Zimmermann) and insect pests negatively affect soybean production; however, little is known about how these herbivores potentially interact to affect soybean yield. Previous studies have shown deer browse on non-crop plants affects insect density and insect-mediated leaf damage, which together reduce plant reproductive output. In soybeans, reproductive output is influenced by direct and indirect interactions of different herbivores.
2. Here, we quantified indirect interactions between two groups of herbivores (mammals and insects) and their effects on soybean growth and yield. We examined responses of insect pest communities along a gradient of deer herbivory (29% to 49% browsed stems) in soybean monocultures.
3. Structural equation models showed that deer browse had direct negative effects on soybean plant height and yield. Deer browse indirectly decreased insect-mediated leaf damage by reducing plant height. Deer browse also indirectly increased pest insect abundance through reductions in plant height. Similarly, deer herbivory had an indirect positive effect on leaf carbon: nitrogen ratios through changes in plant height, thereby decreasing leaf nutrition.
4. These results suggest that pest insect abundance may be greater on soybean plants in areas of higher deer browse, but deer browse may reduce insect herbivory through reduced leaf nutrition.

     

Explaining differential herbivory in sun and shade: the case of Aristotelia chilensis saplings

Differential herbivory in contrasting environments is commonly explained by differences in plant traits. When several plant traits are considered, separate correlation analyses between herbivory and candidate traits are typically conducted. This makes it difficult to discern which trait best explain the herbivory patterns, or to avoid spurious inferences due to correlated characters. Aristotelia chilensis saplings sustain greater herbivory in shaded environments than in open habitats. We measured alkaloids, phenolics, trichomes, leaf thickness and water content in the same plants sampled for herbivory. We conducted a multiple regression analysis to estimate the relationship between herbivory and each plant trait accounting for the effect of correlated traits, thus identifying which trait(s) better explain(s) the differential herbivory on A. chilensis. We also estimated insect abundance in both light environments. Palatability bioassays tested whether leaf consumption by the main herbivore on A. chilensis was consistent with field herbivory patterns. Overall insect abundance was similar in open and shaded environments. While saplings in open environments had thicker leaves, lower leaf water content, and higher concentration of alkaloids and phenolics, no difference in trichome density was detected. The multiple regression analysis showed that leaf thickness was the only trait significantly associated with herbivory. Thicker leaves received less damage by herbivores. Sawfly larvae consumed more leaf tissue when fed on shade leaves. This result is consistent with field herbivory and, together with results of insect abundance, renders unlikely that the differential herbivory in A. chilensis was due to greater herbivory pressure in open habitats.     

Bird predation enhances tree seedling resistance to insect herbivores in contrasting forest habitats

According to the associational resistance hypothesis, neighbouring plants are expected to influence both the insect herbivore communities and their natural enemies. However, this has rarely been tested for the effects of canopy trees on herbivory of seedlings. One possible mechanism responsible for associational resistance is the indirect impact of natural enemies on insect herbivory, such as insectivorous birds. But it remains unclear to what extent such trophic cascades are influenced by the composition of plant associations (i.e. identity of ‘associated’ plants). Here, we compared the effect of bird exclusion on insect leaf damage for seedlings of three broadleaved tree species in three different forest habitats. Exclusion of insectivorous birds affected insect herbivory in a species-specific manner: leaf damage increased on Betula pendula seedlings whereas bird exclusion had no effect for two oaks (Quercus robur and Q. ilex). Forest habitat influenced both the extent of insect herbivory and the effect of bird exclusion. Broadleaved seedlings had lower overall leaf damage within pine plantations than within broadleaved stands, consistent with the resource concentration hypothesis. The indirect effect of bird exclusion on leaf damage was only significant in pine plantations, but not in exotic and native broadleaved woodlands. Our results support the enemies hypothesis, which predicts that the effects of insectivorous birds on insect herbivory on seedlings are greater beneath non-congeneric canopy trees. Although bird species richness and abundance were greater in broadleaved woodlands, birds were unable to regulate insect herbivory on seedlings in forests of more closely related tree species.     

Elevational gradients in plant defences and insect herbivory: recent advances in the field and prospects for future research

Classic research on elevational gradients in plant–herbivore interactions holds that insect herbivore pressure is stronger under warmer, less seasonal climates characteristic of low elevations, and that this in turn selects for increased defence in low‐ (relative to high‐) elevation plants. However, recent work has questioned this paradigm, arguing that it overly simplifies the ecological complexity in which plant–insect herbivore interactions are embedded along elevational gradients. Numerous biotic and abiotic factors vary with elevation, and their simultaneous influences are the focus of current work on elevational gradients in insect herbivory and plant defences. The present review 1) synthesizes current knowledge on elevational gradients in plant–insect herbivore interactions; 2) critically analyses research gaps and highlights recent advances that contribute to filling these gaps; and 3) outlines new research opportunities to uncover underlying mechanisms and build towards a unified theory on elevational gradients. We conclude that the next generation of studies should embrace community complexity – including multi‐trophic dynamics and the multivariate nature of plant defence – and to do so by combining observational data, manipulative experiments and emerging analytical tools.     

Field evidence for indirect interactions between foliar‐feeding insect and root‐feeding nematode communities on Nicotiana tabacum

Abstract 1. As herbivory often elicits systemic changes in plant traits, indirect interactions via induced plant responses may be a pervasive feature structuring herbivore communities. Although the importance of this phenomenon has been emphasised for herbivorous insects, it is unknown if and how induced responses contribute to the organisation of other major phytoparasitic taxa. 2. Survey and experimental field studies were used to investigate the role of plants in linking the dynamics of foliar‐feeding insects and root‐feeding nematodes on tobacco, Nicotiana tabacum. 3. Plant‐mediated interactions between insects and nematodes could largely be differentiated by insect feeding guild, with positive insect–nematode interactions predominating with leaf‐chewing insects (caterpillars) and negative interactions occurring with sap‐feeding insects (aphids). For example, insect defoliation was positively correlated with the abundance of root‐feeding nematodes, but aphids and nematodes were negatively correlated. Experimental field manipulations of foliar insect and nematode root herbivory also tended to support this outcome. 4. Overall, these results suggest that plants indirectly link the dynamics of divergent consumer taxa in spatially distinct ecosystems. This lends support to the growing perception that plants play a critical role in propagating indirect effects among a diverse assemblage of consumers.     

Insect herbivory in climber–host shrubs associations: Benefit or detriment?

Spatial proximity between different plant species could modify the sign (positive or negative) of plant–herbivore interaction. The chance of a plant being detected and colonized by herbivorous insects depends not only on the plant's own traits but also on the identity of the neighbouring plants that grow with it. The closest proximity between plants occurs in climbers and their host. We conducted a field experiment to assess the effect of spatial association between a climber plant, Vicia nigricans (Fabaceae), and two host shrubs, Berberis buxifolia (Berberidaceae) and Schinus patagonica (Anacardiaceae), on insect herbivory levels, reproductive output and growth. The presence and identity of the host shrubs affected the herbivory levels of the climber V. nigricans, but not the reproductive output. For the climber, the probability of being attacked by insects could depend on the characteristics of the host shrub. Taking the opposite perspective, climber association affected different traits of the host shrubs. The association with the climber decreased leaf damage (positive), tended to decrease leaf production (negative) and did not affect reproductive output (neutral). Our findings suggest that spatial association between plant species could change the sign of the interactions between plants and insects affecting different traits. By taking into account the perspective of both plants involved in the association, this study shows and emphasizes that plant–animal interactions strongly depend on the community context.     

Ant–scale mutualism increases scale infestation,decreases folivory,and disrupts biological control in restored tropical forests

Ant–hemipteran mutualisms can have positive and negative effects on host plants depending on the level of hemipteran infestation and plant protection conferred by ants against folivory. Differential effects of such mutualisms on plant survival are well documented in undisturbed and ant-invaded systems, but few have explored how anthropogenic disturbance affects interactions between hemipterans and native ant species and what the consequences may be for recovering ecosystems. Within a fragmented landscape in Costa Rica, restored tropical forests harbor a mutualism between the native ant Wasmannia auropunctata and the scale insect Alecanochiton marquesi on the abundant, early-successional tree Conostegia xalapensis. I added A. marquesi scales to C. xalapensis seedlings and either allowed or excluded W. auropunctata to investigate if this mutualism leads to increased scale infestation, decreased scale mortality, and decreased folivory. I also examined whether these effects are mediated by the percentage of remnant forest cover in the landscape. I found that seedlings with ants excluded had fewer scale insects and higher herbivory than plants with ants present. I also found evidence that scale mortality due to fungal attack and parasitism was higher on ant-excluded versus ant-allowed seedlings but only at sites with high surrounding landscape forest cover. Together, these results suggest that mutualisms between scale insects and native ants can promote scale infestation, reduce folivory on native plant species, and potentially disrupt biological control of scale insects in recovering tropical forests. Further, my experiment underscores the importance of remnant tropical forests as sources of biological control in anthropogenically disturbed landscapes. Abstract in Spanish is available with online material.     

Plant transpiration at high elevations: Theory,field measurements,and comparisons with desert plants

Summary The influence of elevational changes on plant transpiration was evaluated using leaf energy balance equations and well-known elevational changes in the physical parameters that influence water vapor diffusion. Simulated transpirational fluxes for large leaves with low and high stomatal resistances to water vapor diffusion were compared to small leaves with identical stomatal resistances at elevations ranging from sea level to 4 km. The specific influence of various air temperature lapse rates was also tested. Validation of the simulated results was accomplished by comparing actual field measurements taken at a low elevation (300 m) desert site with similar measurements for a high elevation (2,560 m) mountain research site. Close agreement was observed between predicted and measured values of transpiration for the environmental and leaf parameters tested.Substantial increases in solar irradiation and the diffusion coefficient for water vapor in air (D _wv) occurred with increasing elevation, while air and leaf temperatures, the water vapor concentration difference between the leaf and air, longwave irradiation, and the thermal conductivity coefficient for heat in air decreased with increasing elevation. These changes resulted in temperatures for sunlit leaves that were further above air temperature at higher elevations, especially for large leaves. For large leaves with low stomatal resistances, transpirational fluxes for low-elevation desert plants were close to those predicted for high-elevation plants even though the sunlit leaf temperatures of these mountain plants were over 10°C cooler. Simulating conditions with a low air temperature lapse rate (0.003° C m^-1 and 0.004° C m^-1) resulted in predicted transpirational fluxes that were greater than those calculated for the desert site. Transpiration for smaller leaves decreased with elevation for all lapse rates tested (0.003° C m^-1 to 0.010° C m^-1). However, transpirational fluxes at higher elevations were considerably greater than expected for all leaves, especially larger leaves, due to the strong influence of increased solar heating and a greater D _wv. These results are discussed in terms of similarities in leaf structure and plant habit observed among low-elevation desert plants and high-elevation alpine and subalpine plants.