Seed predation by insects across a tropical forest precipitation gradient

1. Pre‐dispersal predation of seeds by insects can be an important source of plant mortality, with consequences for plant population dynamics and community diversity. 2. The intensity and host‐specificity of natural enemies, including seed predators, is predicted to vary systematically across environmental gradients. These trends could contribute to large‐scale patterns in diversity, such as the widely observed positive relationship between plant species richness and precipitation. However, fundamental information on inter‐ and intraspecific seed predation is lacking at the landscape scale. 3. We assessed the intensity of seed predation by insects at eight forest sites spanning a steep precipitation and plant species‐richness gradient in Panama. We dissected freshly abscised fruits and seeds of woody plants to measure rates of predation, and assessed host‐specificity by rearing insects from them. 4. On average, 22.6% of dissected seeds were predated across 31 host species. Species‐specific and site‐level seed predation rates and the number of seed predator species reared per host were not significantly associated with annual rainfall or dry season water deficit. 5. In total, 45 seed predator morphospecies were reared from seeds of 16 plant species. Host‐specificity was high, with 91% of seed predator morphospecies associated with just one plant species. 6. Our results support evidence that pre‐dispersal insect seed predators are highly host‐specific and exhibit great intraspecific, interspecific and landscape‐scale (i.e. between‐site) variation in seed predation intensity. Host‐specific seed predators, particularly those causing moderate to high seed predation rates, could influence plant population dynamics and local community structure

Leaf vein length per unit area is not intrinsically dependent on image magnification: avoiding measurement artifacts for accuracy and precision.

Leaf vein length per unit leaf area (VLA; also known as vein density) is an important determinant of water and sugar transport, photosynthetic function, and biomechanical support. A range of software methods are in use to visualize and measure vein systems in cleared leaf images; typically, users locate veins by digital tracing, but recent articles introduced software by which users can locate veins using thresholding (i.e. based on the contrasting of veins in the image). Based on the use of this method, a recent study argued against the existence of a fixed VLA value for a given leaf, proposing instead that VLA increases with the magnification of the image due to intrinsic properties of the vein system, and recommended that future measurements use a common, low image magnification for measurements. We tested these claims with new measurements using the software LEAFGUI in comparison with digital tracing using ImageJ software. We found that the apparent increase of VLA with magnification was an artifact of (1) using low-quality and low-magnification images and (2) errors in the algorithms of LEAFGUI. Given the use of images of sufficient magnification and quality, and analysis with error-free software, the VLA can be measured precisely and accurately. These findings point to important principles for improving the quantity and quality of important information gathered from leaf vein systems

Intraspecific leaf trait variability along a boreal-to-tropical community diversity gradient

Disentangling the mechanisms that shape community assembly across diversity gradients is a central matter in ecology. While many studies have explored community assembly through species average trait values, there is a growing understanding that intraspecific trait variation (ITV) can also play a critical role in species coexistence. Classic biodiversity theory hypothesizes that higher diversity at species-rich sites can arise from narrower niches relative to species-poor sites, which would be reflected in reduced ITV as species richness increases. To explore how ITV in woody plant communities changes with species richness, we compiled leaf trait data (leaf size and specific leaf area) in a total of 521 woody plant species from 21 forest communities that differed dramatically in species richness, ranging from boreal to tropical rainforests. At each forest, we assessed ITV as an estimate of species niche breadth and we quantified the degree of trait overlap among co-occurring species as a measure of species functional similarity. We found ITV was relatively invariant across the species richness gradient. In addition, we found that species functional similarity increased with diversity. Contrary to the expectation from classic biodiversity theory, our results rather suggest that neutral processes or equalizing mechanisms can be acting as potential drivers shaping community assembly in hyperdiverse forests.Leaf data used to come to this manuscript resulted from many different studies involving different funding sources: European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 265171; Spanish-funded project REMEDINAL3eCM (S2013/MAE-2719); Ecometas excellence network (CGL2014-53840-REDT); a FPU grant by the Spanish Government (AP2010-5600); a Marie Curie IEF fellowship (FP7-PEOPLE-2011-IEF. no. 302445);Peer Reviewe

The role of herbivorous insects and pathogens in the regeneration dynamics of Guazuma ulmifolia in Panama

A significant proportion of the mortality of rainforest trees occurs during early life stages (seeds and seedlings), but mortality agents are often elusive. Our study investigated the role of herbivorous insects and pathogens in the early regeneration dynamics of Guazuma ulmifolia (Malvaceae), an important tree species in agroforestry in Central America. We reared pre-dispersal insect seed predators from G. ulmifolia seeds in Panama. We also carried out an experiment, controlling insects and pathogens using insecticide and/or fungicide treatments, as well as seed density, and compared survivorship of G. ulmifolia seeds and seedlings among treatments and relative to untreated control plots. We observed (1) high pre-dispersal attack (92%) of the fruits of G. ulmifolia, mostly by anobiine and bruchine beetles; (2) negligible post-dispersal attack of isolated seeds by insects and pathogens; (3) slow growth and high mortality (> 95%) of seedlings after 14 weeks; (4) low insect damage on seedlings; and (5) a strong positive correlation between seedling mortality and rainfall. We conclude that for G. ulmifolia at our study site the pre-dispersal seed stage is by far the most sensitive stage to insects and that their influence on seedling mortality appears to be slight as compared to that of inclement weather. Thus, the regeneration of this important tree species may depend on effective primary dispersal of seeds by vertebrates (before most of the seed crop is lost to insects), conditioned by suitable conditions in which the seedlings can grow