Interactions between Ants and Non‐myrmecochorous Fruits in Miconia (Melastomataceae) in a Neotropical Savanna

The aim of this study was to evaluate the role of ants as secondary seed dispersers of six primarily bird‐dispersed Miconia species in the cerrados of southeastern Brazil. Vertebrate exclosure and seed germination experiments were performed for M. albicans, M. alborufescens, M. corallina, M. ferruginata, M. ibaguensis, and M. irwinii. Excluding vertebrates did not significantly alter fruit removal rate for any of the Miconia species relative to open controls. Fruits on stalks and fallen fruits were removed and transported to nests mainly by species of Atta, Acromyrmex, and Ectatomma (dispersal distance ranging from 0.1 to 45.2 m), while Camponotus ants tended to be observed removing the fruit pulp (seed cleaning) where the fruits were found. Seed manipulation by Atta decreased germination of M. irwinii, but not M. ferruginata. Germination did not occur in intact fruits, and thus seed cleaning was an important service provided by the ants. Ant nest soils did not inhibit germination of any of the Miconia species, suggesting they are a good substrate for long‐lived Miconia seeds. We conclude that ant activity could have important effects on the fate of Miconia seeds adapted for bird dispersal.     

When condition trumps location: seed consumption by fruit‐eating birds removes pathogens and predator attractants

Seed ingestion by frugivorous vertebrates commonly benefits plants by moving seeds to locations with fewer predators and pathogens than under the parent. For plants with high local population densities, however, movement from the parent plant is unlikely to result in ‘escape’ from predators and pathogens. Changes to seed condition caused by gut passage may also provide benefits, yet are rarely evaluated as an alternative. Here, we use a common bird‐dispersed chilli pepper (Capsicum chacoense) to conduct the first experimental comparison of escape‐related benefits to condition‐related benefits of animal‐mediated seed dispersal. Within chilli populations, seeds dispersed far from parent plants gained no advantage from escape alone, but seed consumption by birds increased seed survival by 370% – regardless of dispersal distance – due to removal during gut passage of fungal pathogens and chemical attractants to granivores. These results call into question the pre‐eminence of escape as the primary advantage of dispersal within populations and document two overlooked mechanisms by which frugivores can benefit fruiting plants.     

Relationships of subalpine forest fires in the Colorado Front Range with interannual and multidecadal‐scale climatic variation

Aim An understanding of past relationships between fire occurrence and climate variability will help to elucidate the implications of climate‐change scenarios for future patterns of wildfire. In the present study we investigate the relationships between subalpine‐zone fire occurrence and climate variability and broad‐scale climate patterns in the Pacific and Atlantic Oceans at both interannual and multidecadal time‐scales. Location The study area is the subalpine zone of Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa), and lodgepole pine (Pinus contorta) in the southern sector of the Rocky Mountain National Park, which straddles the continental divide of the northern Colorado Front Range. Methods We compared years of widespread fire from AD 1650 to 1978 for the subalpine zone of southern Rocky Mountain National Park, with climate variables such as measures of drought, and indices such as the El Niño–Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the Atlantic Multidecadal Oscillation (AMO). Results Years of extensive subalpine‐zone fires are significantly related to climate variability, phases of ENSO, the PDO, and the AMO, as well as to phase combinations of ENSO, the PDO, and the AMO at both interannual and centennial time‐scales. Main conclusions Years of extensive fires are related to extreme drought conditions and are significantly related to the La Niña phase of ENSO, the negative (cool) phase of the PDO, and the positive (warm) phase of the AMO. The co‐occurrence of the phase combination of La Niña‐negative PDO‐positive AMO is more important to fire occurrence than the individual influences of the climate patterns. Low‐frequency trends in the occurrence of this combination of climate‐pattern phases, resulting from trends in the AMO, are the primary climate pattern associated with periods of high fire occurrence (1700–89 and 1851–1919) and a fire‐free period (1790–1850). The apparent controlling influence of the AMO on drought and years of large fires in the subalpine forests of the Colorado Front Range probably applies to an extensive area of western North America.     

Selection on fruit traits is mediated by the interplay between frugivorous birds,fruit flies,parasitoid wasps and seed‐dispersing ants

Every organism on Earth must cope with a multitude of species interactions both directly and indirectly throughout its life cycle. However, how selection from multiple species occupying different trophic levels affects diffuse mutualisms has received little attention. As a result, how a given species amalgamates the combined effects of selection from multiple mutualists and antagonists to enhance its own fitness remains little understood. We investigated how multispecies interactions (frugivorous birds, ants, fruit flies and parasitoid wasps) generate selection on fruit traits in a seed dispersal mutualism. We used structural equation models to assess whether seed dispersers (frugivorous birds and ants) exerted phenotypic selection on fruit and seed traits in the spiny hackberry (Celtis ehrenbergiana), a fleshy‐fruited tree, and how these selection regimes were influenced by fruit fly infestation and wasp parasitoidism levels. Birds exerted negative correlational selection on the combination of fruit crop size and mean seed weight, favouring either large crops with small seeds or small crops with large seeds. Parasitoids selected plants with higher fruit fly infestation levels, and fruit flies exerted positive directional selection on fruit size, which was positively correlated with seed weight. Therefore, higher parasitoidism indirectly correlated with higher plant fitness through increased bird fruit removal. In addition, ants exerted negative directional selection on mean seed weight. Our results show that strong selection on phenotypic traits may still arise in perceived diffuse species interactions. Overall, we emphasize the need to consider diverse direct and indirect partners to achieve a better understanding of the mechanisms driving phenotypic trait evolution in multispecies interactions.