Short-term seasonal habitat facilitation mediated by an insect herbivore
Harvey, Jeffrey A. ; Ode, Paul J. ; Malcicka, Miriama ; Gols, Rieta - \ 2016
Basic and Applied Ecology 17 (2016)5. - ISSN 1439-1791 - p. 447 - 454.
Clubiona phragmitis - Community - Earwig - Ecological interactions - Forficula auricularia - Porcellio scaber - Spider - Woodlice
In nature some organisms may facilitate others by creating shelter or other niches that they use for variable periods. We describe a natural multitrophic-species complex in the Netherlands involving a plant, the common hogweed (Heracleum sphondylium) a specialist chewing herbivore, the parsnip webworm (Depressaria pastinacella) and various arthropods associated with them. Larvae of D. pastinacella feed on H. sphondylium seeds and, after they have finished feeding, chew holes in the hollow stems where they pupate. In some areas of the country almost 50% of plants are attacked by webworms. The holes are used by other arthropods to gain access to the stems including herbivores, omnivores, predators and decomposers. The duration of plant occupancy varies between 3 and 4 months, until the plants die. Plants without moth-produced holes were always free of other arthropods, whereas plants with holes, in addition to pupae (and/or mummified-parasitized webworm larvae), often contained many woodlice, earwigs and/or spiders. Earwigs and woodlice perform important ecological functions as predators (in orchards) and decomposers respectively. Our results show that the simple biological activity of one herbivore species can have at least short-term effects on the local arthropod community. In der Natur können manche Organismen andere begünstigen, indem sie Refugien oder andere Nischen erschaffen, die sie für unterschiedliche Zeiträume nutzen. Wir beschreiben einen natürlichen multitrophischen Artenkomplex in den Niederlanden, der den Wiesen-Bärenklau (Heracleum sphondylium), die Pastinakmotte (Depressaria pastinacella) und verschiedene mit ihnen assoziierte Arthropoden umfasst. Die Larven der Pastinakmotte fressen an Bärenklausamen und beißen später Löcher in die hohlen Stengel, um sich darin zu verpuppen. Die Löcher werden von anderen Arthropoden genutzt, um Zugang ins Stengelinnere zu erhalten. Die Pflanze wird für etwa drei bis vier Monate besiedelt bis sie abstirbt. Pflanzen ohne Mottenlöcher wurden niemals von anderen Arthropoden besiedelt, während Stengel mit Löchern zusätzlich zu den Mottenpuppen bzw. parasitierten Larvenmumien häufig viele Asseln, Ohrwürmer und/oder Spinnen enthielten. Ohrwürmer und Asseln erfüllen wichtige ökologische Funktionen als Räuber in Obstplantagen bzw. als Zersetzer. Unsere Ergebnisse zeigen, dass die einfache biologische Aktivität einer Herbivorenart zumindest kurzfristige Auswirkungen auf die lokale Arthropodengemeinschaft haben kann.
Effects of intra- and interspecific competition on the sensitivity of Daphnia magna populations to the fungicide carbendazim
Arco, Ana Isabel Del; Rico Artero, Andreu ; Brink, P.J. van den - \ 2015
Ecotoxicology 24 (2015)6. - ISSN 0963-9292 - p. 1362 - 1371.
Carbendazim - Competition - Ecological interactions - Ecological risk assessment - Pesticides
The ecological risk assessment of pesticides is generally based on toxicity data obtained from single-species laboratory experiments and does not take into account ecological interactions such as competition or predation. Intraspecific and interspecific competition are expected to result in additional stress and might increase the sensitivity of aquatic populations to pesticide contamination. To test this hypothesis, the effects of the fungicide carbendazim were assessed on the population dynamics of the micro-crustacean Daphnia magna under different levels of intraspecific and interspecific competition for an algal food resource, using the rotifer Brachionus calyciflorus as competing species. The experiments were performed in glass jars with three different carbendazim concentrations (i.e., 50, 100 and 150 µg/L), and had a duration of 25 days, with a 4-day pre-treatment period in which competition was allowed to take place and a 21-day exposure period. The endpoints evaluated were D. magna total population abundance and population structure. Results of these experiments show that competition stress on its own had a significant influence on shaping D. magna population’s structure, however, a different response was observed in the intraspecific and interspecific competition experiments. The use of a 4-day pre-treatment period in the intraspecific experiment already led to an absence of interactive effects due to the quick abundance confluence between the different intraspecific treatments, thus not allowing the observation of interactive effects between competition and carbendazim stress. Results of the interspecific competition experiment showed that rotifers were quickly outcompeted by D. magna and that D. magna even profited from the rotifer presence through exploitative competition, which alleviated the original stress caused by the algal resource limitation. These experiments suggest that competition interactions play an important role in defining population-level effects of pesticides in a more complex way than was hypothesized (“increasing competition leading to a sensitivity increase”), as the interspecific experiment showed. Therefore, these should be taken into account in the extrapolation of single-species toxicity data to protect higher levels of biological organization.