Agricultural intensification and cereal aphid–parasitoid–hyperparasitoid food webs: network complexity, temporal variability and parasitism rates

Abstract

Agricultural intensification (AI) is currently a major driver of biodiversity loss and related ecosystem functioning decline. However, spatio-temporal changes in community structure induced by AI, and their relation to ecosystem functioning, remain largely unexplored. Here, we analysed 16 quantitative cereal aphid–parasitoid and parasitoid–hyperparasitoid food webs, replicated four times during the season, under contrasting AI regimes (organic farming in complex landscapes vs. conventional farming in simple landscapes). High AI increased food web complexity but also temporal variability in aphid–parasitoid food webs and in the dominant parasitoid species identity. Enhanced complexity and variability appeared to be controlled bottom-up by changes in aphid dominance structure and evenness. Contrary to the common expectations of positive biodiversity–ecosystem functioning relationships, community complexity (food-web complexity, species richness and evenness) was negatively related to primary parasitism rates. However, this relationship was positive for secondary parasitoids. Despite differences in community structures among different trophic levels, ecosystem services (parasitism rates) and disservices (aphid abundances and hyperparasitism rates) were always higher in fields with low AI. Hence, community structure and ecosystem functioning appear to be differently influenced by AI, and change differently over time and among trophic levels. In conclusion, intensified agriculture can support diverse albeit highly variable parasitoid–host communities, but ecosystem functioning might not be easy to predict from observed changes in community structure and composition.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-012-2366-0) contains supplementary material, which is available to authorized users.

Local and Landscape Drivers of Ant Parasitism in a Coffee Landscape

“…Different taxa vary in response to increases in tree diversity, canopy shade, and decreased agrochemical use (Moguel and Toledo 1999, Mas and Dietsch 2003, García Estrada et al 2006, Gagic et al 2012; thus, some taxa may be more sensitive to agricultural landscape changes and act as indicators of habitat simplification (e.g. Pocock andJennings 2008, De la Mora and.…”

Landscape scale study of diversity and interaction in cereal aphids - parasitoids system (Homoptera; Hymenoptera)

“…U tom slučaju se heterogenost sastava najčešće zapravo posredno izražava preko procenta prirodnih i poluprirodnih staništa. Ovaj pristup je iskoriščen u velikom broju studija (Marino & Landis, 1996;Menalled et al, 1999Menalled et al, , 2003Thies & Tscharntke, 1999;Tscharntke, 2000;Kruess, 2003;Steffan-Dewenter, 2003;Costamagna et al, 2004;Bianchi et al, 2005Bianchi et al, , 2006Thies et al, 2003Thies et al, , 2005Thies et al, , 2011Purtauf et al, 2005;Roschewitz et al, 2005;Schmidt & Tscharntke, 2005b;Tscharntke et al, , 2007Brewer et al, 2008;Schmidt et al, 2008;Vollhardt et al, 2008;Holzschuh et al, 2010;Perović et al, 2010;Chaplin-Kramer et al, 2011;Gagic et al, , 2012Winqvist et al, 2011;Caballero-López et al, 2012;Jonsson et al, 2012;Rand et al, 2012;Woltz et al, 2012a,b;Al Hassan et al, 2013;Rusch et al, 2013;Veres et al, 2013). Heterogenost konfiguracije predela pokazuje kakvi su prostorni odnosi pojedinačnih elemenata bez obzira na tip elemenata.…”

“…Ovakav sastav vrsta i velika zastupljenost velike žitne vaši je u skladu sa rezultatima nekoliko prethodnih studija (Petrović, 1996;Sigsgaard, 2002;Schmidt et al, 2003;Roschewitz et al, 2005;Thies et al, 2005;Gagic et al, 2011Gagic et al, , 2012Kos et al, 2012;Al Hassan et al, 2013), ali i u suprotnosti sa studijama koje su zabeležile drugačije odnose relativne zastupljenosti (Tomanović et al, 2008;Caballero-López et al, 2012;Lohaus et al, 2012) kao i drugačiji sastav vrsta (Brewer & Elliott, 2004;Brewer et al, 2008;Caballero-López et al, 2011). Najmanje zastupljena vrsta je bila S. maydis koja je bila prisutna samo u dva kompleksna predela u toku jedne godine.…”

“…Pregledom rezultata sličnih studija (Tomanović & Brajković, 2001;Sigsgaard, 2002;Roschewitz et al, 2005;Vollhardt et al, 2008;Tomanović et al, 2008;Caballero-López et al, 2011, 2012Gagic et al, 2011Gagic et al, , 2012Lohaus et al, 2012;Kos et al, 2012) može se zaključiti da sastav i struktura gilde parazitoida biljnih vašiju značajno varira ne samo između regiona, već i između godina u okviru istog regiona. Imajući u vidu različito ponašanje porazitoida i njihovu preferenciju ka biljnim vašima (Powell & Zhi-Li, 1983;Mackauer & Völkl, 1993;Bueno et al, 2003;Lo Pinto et al, 2004;Langley et al, 2006;Rehman & Powell, 2010) kao i biotičke odnose, pre svega kompeticiju, unutar gilde parazitoida (McBrien & Mackauer, 1990;Brodeur & Rosenheim, 2000), prisustvo ili odsustvo određenih vrsta parazitoida, kao i njihova relativna zastupljenost mogu imati veliki uticaj na uspešnost biološke kontrole biljnih vaši.…”

“…Objašnjenje ovog fenomena se može naći u biologiji prisutnih vrsta Hipoteza da će u kompleksnim predelima procenat parazitiranost biti veći je potvrđena iako efekat nije bio konstantan tokom godina. Ovo je u skladu sa rezultatima nekoliko sličnih studija Thies et al, 2005;Gagic et al, 2011Gagic et al, , 2012Rand et al, 2012‚ i delom u Thies et al, 2011 koje ukazuju da u kompleksnim predelima postoje elementi koji pozitivno utiču na paraziotoide. Veći diverzitet vrsta biljnih vašiju koje žive na prirodnim i poluprirodnim staništima može pozitivno uticati na parazitoide obezbeđujući veći izbor alternativnih domaćina.…”