María Calviño-Cancela

Effectiveness of a varied assemblage of seed dispersers of a fleshy‐fruited plant

Disperser effectiveness is the number of new plants resulting from the activity of one disperser relative to other dispersers or to nondispersed seeds. Effectiveness remains largely uninvestigated due to the complexity of its measurement. We measured the effectiveness of seed dispersers (Larus michahellis, Turdus merula, and Oryctolagus cuniculus) of the shrub Corema album (Empetraceae) using a simulation model of the recruitment process that was parameterized with field data of seed dispersal, predation, and seedling emergence and validated with independent data on seedling density. The model allows tracking the fate of seeds dispersed by each animal and estimating, for the first time, disperser effectiveness as seedlings per square meter contributed by each disperser. It also allows quantifying the relative importance of different recruitment processes in determining the quantity and spatial distribution of recruitment. Larus michahellis was the most effective disperser in two of the three habitats studied, contributing 3-125 times more than the other two species, whose lower effectiveness depended mostly on deposition patterns (T. merula) or deleterious effects on seedling emergence (O. cuniculus). The dependence of the plant on each disperser differed between habitats and was the greatest in sparse scrub, where recruitment depended almost exclusively on gulls (90%). Quantity and quality of dispersal were not correlated; quality was a better predictor of disperser effectiveness. Seedling emergence was the most crucial process in determining both the spatial pattern of recruitment among microhabitats (99.8% of variance explained) and the quantity of recruitment within microhabitats (43-83%). A sensitivity analysis showed that increasing seed dispersal improved the recruitment for all dispersers when there was no competition for fruits. However, with limited fruits, increased dispersal of lower quality dispersers reduced overall recruitment. Our results show important differences in effectiveness among dispersers and illustrate the different influences of the components of effectiveness, which varied depending not only on the disperser but also on the circumstances (e.g., type of habitat).

Diverse guilds provide complementary dispersal services in a woodland expansion process after land abandonment

Summary 1. Land abandonment due to increasing depopulation of rural areas is an ongoing trend in developed countries worldwide. Abandoned lands represent an opportunity for ecosystem recovery, an urgent need for biodiversity conservation. Seed dispersal services provided by animals are a key feature for this process. Different dispersers may differentially contribute to plant recruitment under different ecological conditions, leading to complementary dispersal services. 2. We studied the dispersal services, quantified as the contribution to plant recruitment, provided by the main dispersal guilds of Spanish juniper Juniperus thurifera L.: small-to-mediumsized strongly frugivorous birds (thrushes) and medium-to-large-sized carnivorous mammals (red fox and stone marten). To do this, we studied seed fate from seed dispersal to seedling survival during 2 years and estimated seed dispersal effectiveness (seedlings recruited per m 2 ) in two ecological contexts derived from ecosystem recovery after a historical period of degradation: remnant woodlands and old fields. 3. Results showed a clear shift in the contribution to plant recruitment between these guilds, resulting in complementary and non-redundant dispersal services. Thrushes were the main contributors to plant recruitment in woodlands (73%), leading to population growth but with a reduced impact on the colonization of old fields where carnivores contributed to 80% of recruitment (42% red fox, 38% stone marten). The dispersal complementarity observed for thrushes and carnivores is a consequence of their functional diversity, mainly driven by their differences in feeding and movement behaviour. 4. Synthesis and applications. The combination of short-distance, strongly frugivorous dispersers (e.g. passerine birds) together with big generalist frugivores with long-distance movements (e.g. carnivorous mammals) maintained (i) effective seed dispersal services in remnant woodlands and (ii) the connectivity between patches promoting old fields colonization and woodland expansion. Thus, it is in heterogeneous landscape mosaics ecosystems (e.g. agroenvironments) where functionally diverse disperser communities play a key role in ecosystem recovery. By performing effective dispersal services across an array of habitat types, functionally diverse disperser communities assist natural restoration of human-impacted ecosystems all over the world. Thus, dispersal communities provide an important ecosystem service that may replace costly human-mediated restoration projects.

Comparing seed dispersal effectiveness by frugivores at the community level

Seed dispersal effectiveness (SDE) is the contribution of dispersers to plant recruitment and is estimated as the product of the number of seeds dispersed (quantity) and the probability of recruitment of each dispersed seed (quality). Although SDE is a key concept in seed dispersal ecology, few studies estimate SDE and none has a community approach. Oceanic islands, with simple communities, are ideal for this purpose. In this study, we compared the SDE of the main types of dispersers (lizards and passerine birds) at the community level in a given habitat. We estimated SDE using a stochastic simulation model parameterized with empirical data on quantity and quality components measured throughout the recruitment process. Although lizards are highly frugivorous and their density was approximately 20 times higher than that of birds, lizards and birds dispersed a similar quantity of seeds. This may be due to lower intake of seeds by lizards due to their slower metabolism (approximately 20 times lower than birds). This low metabolic rate limits the importance of lizards as seed dispersers, but it is compensated by extraordinarily high lizard densities in the study area (approximately 9600 individuals/km2). High densities of lizards are typical of islands, and this helps to explain why dispersal by lizards seems mainly an island phenomenon. Birds and lizards showed functional complementarity, especially regarding seed dispersal distribution patterns. In fact, lizards dispersed more seeds in shrublands and open sites, and birds in woodlands and beneath canopies, with their joint contribution helping to maximize recruitment. Lizards provided higher SDE than birds for 7 out of 11 plant species. The disperser with a higher quantity for a given plant generally had the higher quality, and plants could be classified as bird- or lizard-dependent for dispersal. This dependence increased when considering SDE instead of dispersal quantity only. Moreover, quality was a better predictor of SDE than quantity, which should be considered when parameterizing interaction networks, as this might affect inferences about their architecture.

GPU Geocorrection for Airborne Pushbroom Imagers

We present a method for real-time geocorrection of images from airborne pushbroom sensors using the hardware acceleration and parallel computing characteristics of modern graphics processing units. This allows very fast geocorrection without accuracy loss with respect to traditional direct methods, with very little computational load for the central processor. Our method is based on a projective texture technique originally developed for fast shadow rendering. By combining the image data with inertial navigation and positioning ancillary data, we correct the image to a digital terrain model (DTM) and produce a geocorrected and georeferenced image. The method works independently of the number of channels of the sensor. Results with an ultralight hyperspectral system show that the speed achieved with standard hardware for a 1-m grid DTM gives better than real-time performance. This allows in-flight inspection of the geocorrected image during acquisition, for more efficient coverage of large target areas. In regard to accuracy, differences with standard ray tracing direct geocorrection remained subpixel.

Anisotropic Inpainting of the Hypercube

Airborne pushbroom sensors produce images by acquiring scenes on a line-per-line basis. Depending on the motions of the aircraft carrying the sensor, the line integration time, and the targeted spatial resolution, missing areas may appear on geocorrected images. Missing pixels in geocorrected images are usually tackled by means of interpolation methods, such as nearest neighbor, but these cause visible artifacts that affect the visual quality of the result and also the performance of processing methods working on geocorrected images. We propose the use of an anisotropic diffusion inpainting method specifically devised for hyperspectral images, show some extreme examples, and discuss its convenience.

Gulls (Laridae) as frugivores and seed dispersers

Many gull species (Laridae) are opportunistic feeders with diverse diets. Seeds and fruits are common in gull diets, often in small proportions but sometimes dominant in certain periods and areas. Moreover, the large body sizes and high population densities of gulls increase their ecological importance. Hence, they can be significant seed dispersers even with relatively few seeds in diets. Gulls are highly mobile and have long gut-retention times, thus may provide long-distance dispersal for plants. Most information of the potential role of gulls as seed dispersers is from dietary studies, not focused on plant–animal interactions, thus the role of gulls on plant population dynamics is little known. Nevertheless, gulls have been shown to be effective dispersers of some coastal plants, and vectors for plant movement to and between islands. Here, I review this topic and hope to stimulate more research into the role of gulls as seed dispersers, particularly in coastal and island habitats.

Alien plant monitoring with ultralight airborne imaging spectroscopy.

Effective management of invasive plants requires a precise determination of their distribution. Remote sensing techniques constitute a promising alternative to field surveys and hyperspectral sensors (also known as imaging spectrometers, with a large number of spectral bands and high spectral resolution) are especially suitable when very similar categories are to be distinguished (e.g. plant species). A main priority in the development of this technology is to lower its cost and simplify its use, so that its demonstrated aptitude for many environmental applications can be truly realized. With this aim, we have developed a system for hyperspectral imaging (200 spectral bands in the 380–1000 nm range and circa 3 nm spectral resolution) operated on board ultralight aircraft (namely a gyrocopter), which allows a drastic reduction of the running costs and operational complexity of image acquisition, and also increases the spatial resolution of the images (circa 5–8 pixels/m2 at circa 65 km/h and 300 m height). The detection system proved useful for the species tested (Acacia melanoxylon, Oxalis pes-caprae, and Carpobrotus aff. edulis and acinaciformis), with user’s and producer’s accuracy always exceeding 90%. The detection accuracy reported corresponds to patches down to 0.125 m2 (50% of pixels 0.5×0.5 m in size), a very small size for many plant species, making it very effective for initial stages of invasive plant spread. In addition, its low operating costs, similar to those of a 4WD ground vehicle, facilitate frequent image acquisition. Acquired images constitute a permanent record of the status of the study area, with great amount of information that can be analyzed in the future for other purposes, thus greatly facilitating the monitoring of natural areas at detailed spatial and temporal scales for improved management.

Accurate Implementation of Anisotropic Diffusion in the Hypercube

Anisotropic diffusion in the hypercube is a powerful image restoration and enhancement tool for hyperspectral imagery. Processing hyperspectral images requires special attention to accuracy, in order to preserve the high spectral precision that characterizes this kind of data. Here, we propose alternative implementations of the method with specific regard to the numerical accuracy of the solution in strict sense. We propose and describe how to apply rotationally invariant finite differences and a local filtering scheme. We also test and discuss their performance on several hyperspectral images.

Dietary characteristics of Emus (Dromaius novaehollandiae) in semi-arid New South Wales, Australia, and dispersal and germination of ingested seeds

Abstract The Emu (Dromaius novaehollandiae) eats a wide range of seeds and other plant material but little is known of the seeds eaten and dispersed in arid Australia. This study aimed to determine the species of seed and fruits eaten by Emus through the year and investigate the effect of the passage of seeds through the Emu gut on seed germination. Emu scats were opportunistically collected in all seasons of 2005 at Nanya Research Station, western New South Wales. Seeds of 29 plant species were retrieved, identified and counted from 221 scats. Seeds of perennial species, such as Belah (Casuarina pauper), Ruby Saltbush (Enchylaena tomentosa), Common Emu-bush (Eremophila glabra) and Nitre-bush (Nitraria billardierei), predominated. Seed composition of scats was more diverse in summer than in winter, autumn and spring. Seeds of Common Emu-bush, Berrigan (Eremophila longifolia) and Sweet Quandong (Santalum acuminatum) showed no germination after passage through the gut. Ruby Saltbush and Nitre-bush showed very low germination rates. The Emu is a generalist feeder, capable of ingesting and dispersing large numbers of plant species. Through high seed consumption and long gut-retention time, Emus could potentially play a significant role in long-distance dispersal of seeds and, through such dispersal, in the vegetation dynamics of arid Australia.

Simplifying methods to assess site suitability for plant recruitment

Few studies link seed dispersal with its demographic consequences, or provide reliable estimates of seed dispersal effectiveness. One reason is the complexity of measuring the suitability for plant recruitment of seed arrival sites. In this study, I compare three methods that differ in the effort required to measure site suitability for seedling recruitment. All are based on the proportion of seeds that become seedlings (seedling-to-seed ratios). Method I is the most detailed and labour intensive. The fate of seeds was followed throughout the different steps of the recruitment process, from fruit removal until seedling emergence, including both seeds dispersed by different animals and undispersed seeds. Method II is based on seed addition experiments. Seeds were sowed in plots, and seedlings emerging were counted in the following two seasons. In Method III, average seed input during dispersal was measured with soil seed bank samples taken in pre- and post-dispersal periods, and seedling emergence estimated with samples of three seasons. Method II provided results similar to those of Method I, which, conversely, provides more insight in the actual processes driving recruitment. Method III, however, systematically underestimated site suitability (seedling-to-seed ratios) by about 50% as compared to the other methods in all microhabitats studied. Relative instead of absolute indices of site suitability were, however, reliable with this method. Method II and III are significantly less costly and could be good alternatives to Method I for some purposes, simplifying future studies on the demographic consequences of seed dispersal and the effectiveness of dispersers.