Spatial and temporal dynamics of two cacti seed banks in a xerophytic shrubland in Mexico City

Background: Soil and aerial seed banks directly affect recruitment in plant populations. Soil banks result as the balance between seed inputs and outputs. Seed bank dynamics vary by species and environmental conditions. Few records on cacti seed banks are available. Questions: What types of seed banks do two cacti genera form in a lava-field reserve? Does seasonality influence the seed bank dynamics? Are inputs and outputs associated to the microenvironment? Studied species: Opuntia tomentosa, O. lassiacantha, Mammillaria haageana subsp. san-angelensis, M. magnimamma. Study site and dates: Xerophytic shrubland in the “Reserva Ecológica del Pedregal de San Ángel” in Mexico City. 2016 to 2018. Methods: We collected soil samples from four microenvironments during the rainy and the dry seasons, searched for seeds and tested their viability. We compared the number of inputs, outputs and viable seed by microenvironment and season. For M. magnimamma, each month we registered fruit maturation and searched for seeds remaining between tubercles. Results: Opuntia seed bank inputs occurred in all microenvironments and in both seasons. Rain favored inputs in hollows by secondary seed dispersal. We registered a large number of outputs caused by germination, granivory and loss of viability. Opuntia seed bank was developed in headland, plain and slope. No Mammillaria seed inputs were found, neither an aerial bank in M. magnimamma. Conclusion: Opuntia seed banks were restricted to microenvironments that provided “safe sites” which stored viable seeds. Mammillaria seed dynamics may hinders recruitment for their populations.

Indirect restoration of ecological interactions: reintroduction of a dung-beetle associated primate increases the recruitment of large seeds

The biased loss of large and medium frugivores alters seed dispersal and plant regeneration. Species reintroductions have been proposed as a strategy to reverse the consequences of species loss. However, the effects of reintroductions on ecological processes are seldom accessed, which hinders the comprehension of reintroductions’ potential to reestablish functioning ecosystems. In this study, we investigate the effect of howler monkey (Alouatta guariba) reintroduction on the plant regeneration of Tijuca National Park (TNP), a defaunated Atlantic Forest fragment. Howlers are folivore-frugivore primates, whose large clumped defecations attract dung beetles, which provide secondary dispersal by burying seeds present in the howlers’ feces. Thus, we expect that the fate of seeds dispersed by howlers will differ from those dispersed by other frugivores present in the Park. We followed the fate of seeds between 3 and 14mm in diameter in three steps of the seed dispersal loop, each one consisting of a different experiment. First, we estimated secondary seed dispersal and burial depth probabilities according to the frugivores’ defecation pattern; then, predation probability in different burial depths and defecation patterns; and, finally, recruitment probability in different burial depths. Considering the final result of the three experiments, the howlers’ reintroduction affected positively the regeneration of large seeds. The fate of 3mm seeds was little affected because they were seldom preyed upon at shallower depths anyway and could not recruit when deeply buried. On the other hand, seeds larger than 3mm reached the seedling stage more frequently when dispersed by howlers than when dispersed by other animals present in the Park. Thus, howler monkey reintroduction in defaunated areas, in addition to smaller frugivores, whose defecation patterns are less attractive for dung beetles, improves the regeneration of large seeds. We hope that this study will stimulate new howler reintroductions in defaunated areas.

The extent, frequency and ecological functions of food wasting by parrots

Anecdotic citations of food wasting have been described for parrots, but we lack a comprehensive knowledge about the extent of this behaviour, and its ecological and evolutionary implications. Here, we combine experimental and observational approaches to evaluate the spatial, temporal, typological and taxonomic extent of food wasting by parrots, to identify the ecological and evolutionary factors driving food wasting, and to assess the incidence of two ecological functions derived from food wasting, such as food facilitation to other animal species and secondary seed dispersal. We found that food wasting is a widespread behaviour found in all the studied parrot species. However, the proportion of food wasted differed among species and throughout the year. Parrots wasted more food during the non-breeding season, when they relied on exotic plants and on unripe fruits or seeds. We also recorded 86 animal species feeding on the food wasted by parrots, 27 of which potentially acted as secondary seed dispersers. Overall, our study emphasizes the universality of food wasting among parrots, and the important implications that this behaviour may have for the species involved (i.e., the parrot, the plant, the other species feeding on wasted food), and for the functioning of the whole ecosystem.