Juan E. Malo

Herbivorous mammals as seed dispersers in a Mediterranean dehesa

Endozoochrous seed dispersal by herbivorous mammals has been verified repeatedly and its possible influence on the structure and function of herbaceous communities has been suggested. Quantitative studies, however, are lacking in the field of seed dispersal via the dung of herbivore guilds in little-altered environments. The present paper analyses seed dispersal via rabbit, fallow deer, red deer and cow dung in a Mediterranean dehesa (open woodland used for hunting and ranching) during the seeding season. Dung seed content was determined by the glasshouse cultivation of eight dung samples from each herbivore, collected fortnightly between February and August. The four herbivores disperse many seeds (spring averages are 6–15 seeds per gram of dry dung and maxima of 25–70) from a large number of species (totals between 52 and 78). Dispersal seems to be mainly determined by seed production of the plant comminity. This is reflected in (i) the dissemination of a high percentage of the species present in the dehesa, (ii) great seasonal variability, related to seed production, in the amount of seeds and number of species dispersed, and (iii) a high semi-quantitative similarity of seed content in the four types of herbivore dung throughout the year. There is also important quantitative variation that depends on animal traits and feeding habits. These results and the characteristics of species found in dung suggest the adaptation of plant species to the dispersal of their seeds via herbivore gut. This process may well have profound implications for vegetation dynamics and the evolution of plant traits.

Extreme long-distance seed dispersal via sheep

Extremely long seed dispersal distances occur as a result of processes such as ocean drift and tornadoes. However, we have found that large numbers of seeds with different morphologies (Trifolium angustifolium, Daucus carota, Hordeum murinum, and Plantago lagopus) are frequently dispersed equivalent distances while attached to migrating ungulates. We determined experimentally that seeds attached to the fleece of traditional nomadic (“transhumant”) sheep are transported distances of up to several hundred kilometers in substantial numbers (ranging from 5–47% of the initial seed population). Given the current and historical importance of migrating herds of sheep (wild and domestic) on different continents, the results of this study highlight the role of adhesion in long-distance dispersal and support the inclusion of migrating ungulates among forces responsible rapid plant migrations (eg following glaciations, invasion events, or in a future global change scenario). Our results also highlight an unexplored ecological consequence of abandoning nomadism.

Herbivore dunging and endozoochorous seed deposition in a Mediterranean dehesa.

Spatial patterns of herbivore defecation within grazing systems are important as they directly affect pasture growth and compo sition. These effects are partially linked to seed dispersal in dung, a little studied process. This paper focuses on: (i) quantification of dung and seeds deposited by herbivores in a Mediterranean grazing system, and (ii) analysis of the spatial variability of dung and seeds deposited within and among plant communities. We carried out year-long monthly quantifications of the depositions of rabbit (Oryctolagus cuniculus), fallow deer (Dama dama), red deer (Cervus elaphus), and cow (Bos taurus) dung to 32 plots distributed in Quercus rotundifolia Lam. and Fraxinus angustifolia Vahl woodlands, mixed scrub, and Cistus ladanifer L. scrub. We also quantified the germinable seed content of dung. The results revealed differences (p < 0.05) in dung deposition, varying (i) among the 4 species, (ii) within species (except for the red deer) among plant communities, and (iii) within plant communities. An average of 735 seeds/m 2 were returned to the soil via dung, with the highest numbers in open woodlands (870‐1,888 seeds/m 2 ) and the lowest numbers in scrubs (83‐315 seeds/m 2 ). Cows dispersed the most seeds (68%), followed by red deer (20%), rabbits (7%), and fallow deer (5%). Spatial variability in deposition led to accumulations of up to several thousand seeds at points covered by the dung. The effect of seed input to the seed bank and on veg etation may be low at large and medium-sized spatial scales, but it can be very important at small scales and for colonization processes.

Sheep gut passage and survival of Mediterranean shrub seeds

Although viable seeds of Mediterranean dry-fruited shrubs are found in herbivore dung, the ecological importance of this observation is still not well understood. We analysed seed retrieval percentages, defecation time and germinability after sheep gut passage for the five most common shrub species of an area in central Spain ( Retama sphaerocarpa , Cytisus scoparius , Halimium umbellatum subsp. viscosum , Cistus ladanifer and Lavandula stoechas subsp. pedunculata ). Five ewes were fed seeds, and their dung was collected regularly during the following week. Seeds were hand-sorted from dung subsamples and tested for germinability. The defecated seeds were clustered in time, with a majority retrieved in the 24–40 h period, although over 1% of the seeds were retained in the gut for more than 72 h. Data suggested a possible link between seed size and retrieval, with medium-sized seeds less damaged (16–23%) than larger and smaller seeds (10–12%), although only a small number of species were studied. Germination results showed an increased percentage of germination after gut passage for H. umbellatum (x 2 test, P C. scoparius ( P L. stoechas did not germinate after gut passage. The results indicate a potential role of herbivore endozoochory for the long-distance dispersal of dry-fruited shrubs and their potential colonization of distant sites.

Endozoochory by native and exotic herbivores in dry areas: consequences for germination and survival of Prosopis seeds.

Mammalian herbivores can play a role in the endozoochorous dispersal of Prosopis seeds in the arid zones of Argentina, and the introduction of exotic mammals can change relevant parameters of the plants reproductive ecology. Our specific goals were to quantify the seeds of Prosopis flexuosa , P. chilensis and P. torquata contained in the faeces of native [mara ( Dolichotis patagonum ), guanaco ( Lama guanicoe )] and exotic [donkey ( Equus asinus ) and hare ( Lepus europaeus )] mammals, and to determine the mortality, germination percentage and germination speed of seeds borne in faeces, compared with those collected from trees. In 2006, seeds were collected directly from trees or removed from mammal faeces. Seeds were counted and classified as apparently healthy or damaged. P. torquata and P. flexuosa seeds were found in the dung of guanaco, hare and mara, whereas only P. flexuosa seeds appeared in donkey faeces. P. chilensis seeds were only found in guanaco faeces. There was a notable relative abundance of seeds contained in small herbivore faeces in comparison to the large herbivores. The passage through the digestive tract of animals modified seed germination capacity and speed, with great variability between animal species. Guanacos had greater effects than donkeys on mortality, germination percentage and germination speed. Differences between the effects of both smaller-sized herbivores on seeds were much smaller.

Niche segregation between wild and domestic herbivores in Chilean Patagonia.

Competition arises when two co-occuring species share a limiting resource. Potential for competition is higher when species have coexisted for a short time, as it is the case for herbivores and livestock introduced in natural systems. Sheep, introduced in the late 19th century in Patagonia, bear a great resemblance in size and diet to the guanaco, the main native herbivore in Patagonia. In such circumstances, it could be expected that the two species compete and one of them could be displaced. We investigated spatial overlap and habitat selection by coexisting sheep and guanaco in winter and in summer. Additionally, we studied habitat selection of the guanaco in a control situation free from sheep, both in summer and winter. We also determined overlap between species in areas with different intensity of use (named preferred and marginal areas) in order to further detect the potential level of competition in the case of overlapping. Guanaco and sheep showed significantly different habitat preferences through all seasons, in spite of their spatial overlap at landscape scale. Additionally, the habitat used by guanaco was similar regardless of the presence or absence of livestock, which further indicates that sheep is not displacing guanaco where they coexist. These results suggest that habitat segregation between guanaco and sheep is due to a differential habitat selection and not to a competitive displacement process. Therefore, the potential for competition is considered low, contrary to what has been previously observed, although this could be a density-dependent result.

Density and habitat use at different spatial scales of a guanaco population (Lama guanicoe) in the Monte desert of Argentina

Abstract The first density estimates of a peripheral guanaco population and its habitat use at different spatial scales are presented for a protected area of Monte desert, Argentina. Transects were surveyed in the wet and dry seasons of 2005. All guanaco herds observed during systematic surveys using roads and tracks were GPS located and their habitat use was identified. Herd size differed significantly between the dry and wet seasons. Population densities differed between wet (0.10–0.12 individuals/km2) and dry seasons (0.60–0.75 individuals/km2). The population estimates ranged from 75 individuals (dry season) to 388 individuals (wet season). Guanacos showed differential habitat use, the first determinant being abiotic factors, such as topography, soil characteristics or microclimate conditions, animals being detected in rougher rocky substrata in the dry season and in open flat terrain in the wet season, followed by a mesoscale selection defined by plant communities. At the latter scale, guanaco preferentially used mixed creosote bushland and saltbush more intensively during the wet season, and open scrub and columnar-cactus slopes in the dry season. The estimated population of this protected area was small but its population density was within the range of other populations and was relatively high for this dry and unproductive area.

Potential ballistic dispersal of Cytisus scoparius (Fabaceae) seeds

Cytisus scoparius (L.) Link (Fabaceae) has a ballistic type of primary seed-dispersal mechanism in which its legumes dehisce suddenly when they dry. This paper presents an experimental approach to the measurement and modeling of distances reached by seeds under optimum dispersal conditions. Branchlets of the species carrying mature legumes were collected and attached to 1.20-m-high platforms on a flat roof terrace. For 2 weeks, daily measurements were made of distances attained by seeds ejected from legumes in the previous 24 h. Seeds were found at a distance of 2343 ± 113 mm (mean ± s.e., n = 245), with 10.2% of recorded distances greater than 5 m and some about 7 m. The mixture model fitted to the distances traveled by seeds allows the mathematical isolation of two underlying processes, the ballistic projection of seeds by dehiscent legumes (nearly 49% of seeds, reaching 3686 ± 1797 mm) and the barochorous dispersal of the remaining seeds in the platform environs (1254 ± 1254 mm). Modeling shows that seeds dispersed ballistically reach locations at some distance from the shrub crown, with low densities of sibling seeds—a potential advantage for the establishment of new individuals.

Abiotic gradients drive floristic composition and structure of plant communities in the Monte Desert

La definicion de comunidades discretas de plantas en zonas deserticas es complejo debido tanto a su homogeneidad a gran escala como a su heterogeneidad a pequena escala, lo que acaba generando dificultades para la toma de decisiones de conservacion. En este trabajo analizamos las comunidades de plantas del sector mas arido del Desierto del Monte en funcion de su estructura y composicion floristica. Se han utilizado tambien variables ambientales estimadas a pequena escala como la pendiente o la superficie de roca, suelo desnudo y hojarasca, asi como variables que operan a mayor escala como la diversidad de especies, la composicion floristica y la similitud dentro y entre localidades. Los analisis de composicion floristica resaltaron la dificultad para segregar diferentes comunidades debido al elevado nivel de heterogeneidad interna y de solapamiento floristico entre las distintas localidades estudiadas. Solo la comunidad situada en el extremo del gradiente de humedad edafica, el algarrobal, se segrego del resto. La ordenacion realizada sobre las variables estructurales en funcion del tipo de sustrato y de la cobertura arborea y de matorral segrego mejor las diferentes comunidades. Nuestros resultados muestran la dificultad para diferenciar comunidades de plantas en desiertos templados, sugiriendo la existencia de ensamblajes de especies relativamente estables en los extremos de los gradientes y de una gran heterogeneidad dentro y entre localidades. Las comunidades de plantas, por tanto, no pueden ser definidas unicamente por variables floristicas, sino que es preciso incluir informacion ambiental.

Community Response of Mammalian Predators and Their Prey to Motorways: Implications for Predator–Prey Dynamics

Understanding the interactions between predators and prey is essential for predicting the effects of disturbances to ecosystems. Motorways produce changes in the surrounding biotic and abiotic environment and hence have multiple impacts on wildlife. Some species are known to change their activity patterns in the proximity of motorways but the implications for the structure of food webs are unknown. This study analyzes the activity patterns of both mammalian predators and their prey species near nine motorways in attempt to clarify how motorways affect the mammalian community. Habitat structural variables were also sampled to control the effects of microhabitat on relative prey abundance. Our results revealed different activity patterns of both predators and prey near motorways that are independent of structural differences in microhabitat. Both the red fox and small mammals were found to use the zone close to the motorways more frequently, whereas lagomorphs and mustelids were less active there. These differences suggest that motorways favor the population of the predator that is most tolerant of human activity, the red fox, whose activity could have both direct and indirect effects on that of other members of the predator and prey community. On the one hand, the red fox seems to act as “top predator” and mustelids to follow a “safety match” strategy avoiding the area close to the motorway where fox is more active. On the other hand, abundances of prey species are negatively associated with the activity of their most frequent predators. This study is the first to assess how the proximity to motorways affects the activity of mammals in two levels of the food web and opens the field for research to understand the processes driving the detected patterns. Moreover, such effects at the community scale should be taken into account when evaluating the impacts of motorways on the surrounding ecosystems.