José Antonio Barrientos

TERRITORIALITY IN A CANNIBALISTIC BURROWING WOLF SPIDER

Field experiments to test the hypothesis that a cannibalistic species is territorial are rare. We conducted two field experiments to test the hypothesis that adult females of the Mediterranean tarantula, Lycosa tarentula (L.) are territorial. In a relatively long-term experiment we placed a female intruder in an artificial burrow within the hypothesized territory of a resident. The intruders disappeared from their burrows at 7× the rate of spiders in a reference and two control treatments. Residency status, not relative size, determined whether the intruder or the resident remained, and evidence suggests that the winner frequently cannibalized the loser. We also conducted a short-term field experiment in which we induced encounters between females. The results were consistent with territorial defense because escalation was more likely if spiders were similar in size, and cannibalism, the outcome of one-third of the encounters, occurred only after escalation. Thus, adult females of the Mediterranean tarantula are territorial, and cannibalism may be a consequence of territorial defense.

Ant versus bird exclusion effects on the arthropod assemblage of an organic citrus grove

1. Predation‐exclusion experiments have highlighted that top‐down control is pervasive in terrestrial communities, but most of these experiments are simplistic in that they only excluded a single group of predators and the effect of removal was evaluated on a few species from the community. The main goal of our study was to experimentally establish the relative effects of ants and birds on the same arthropod assemblage of canopy trees.

Differential ant exclusion from canopies shows contrasting top-down effects on community structure

Predators have far-reaching effects on communities by triggering top-down trophic cascades that influence ecosystem functioning. Omnivory and intraguild interactions between predators give rise to reticulate food webs and may either strengthen or dampen trophic cascades depending on context. Disentangling the effects of multiple predator species is therefore crucial for predicting the influence of predators on community structure. We focused on ants as dominant generalist predators in arthropod communities and set up a differential ant exclusion from canopies to examine its effects on assemblage species composition and densities of five arthropod groups (psocopterans, aphids, spiders, heteropterans and beetles). We coupled a glue band with tubes allowing only the ant Lasius grandis to reach the canopies to isolate its effect from the rest of crawling predators (ants, earwigs) and compared it against a full exclusion and a control. L. grandis alone had widespread effects on assemblage species composition, with contrasting species-specific responses within groups, where some species affected by L. grandis presence were not further affected by the presence of the whole crawling predator assemblage, and vice versa. Overall, L. grandis caused two- to threefold decreases of generalist predators and a threefold increase of aphids. However, it lacked further top-down effects on primary consumers, which only emerged when all crawling predators were present. This differential exclusion demonstrates the distinctive and widespread intraguild effects on community structure of a single ant species that contrast with the top-down effects exerted by the whole crawling predator assemblage.

Interacción de la red áfido-parasitoide-hormiga en plantas asociadas a un cultivo ecológico de cítricos

Fallas Henriquez, A., Molina-Murillo, S. 2017. Methodological proposal to quantify and to compensate the agroecosystem services generated by the good agricultural practices of small-farmers. Ecosistemas 26(3): 89-102. Doi.: 10.7818/ECOS.2017.26-3.11 A diversified and less intensive management of agricultural systems produces agroecosystem services that are often not estimated nor compensated in developing countries. The main objective of this study was to create a tool that allows quantification of agroecosystemic services (SAgro) generated in agroforestry peasant farms, and additionally estimate compensation values. Following an initial test in 2013 on 10 farms, an important bibliographical review was carried out, the consultation of experts, and the evaluation in 2015 of 50 farms at the national level, most of them members of the National Agroforestry Union (UNAFOR) of Costa Rica. As a result, a tool was developed to measure in an agile, flexible and economical way the ecosystem services generated by good agricultural practices produced by small producers (peasants) both for their agricultural system as well as the forest system. We also found that the size of farms is not necessarily the determining factor for the production of agroecosystem services, but rather the type of management practices and investments made. In this process, it was estimated that with an average compensation of US

Intriguing compensation by adult female spiders for food limitation experienced as juveniles

271.6 per agricultural hectare per year, the production or maintenance of agroecosystem services could be encouraged through good agricultural practices.