How Rapidly Do Invasive Birch Forest Geometrids Recruit Larval Parasitoids? Insights from Comparison with a Sympatric Native Geometrid
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Biol Invasions (2013) 15:1573–1589 DOI 10.1007/s10530-012-0393-8 ORIGINAL PAPER How rapidly do invasive birch forest geometrids recruit larval parasitoids? Insights from comparison with a sympatric native geometrid O. P. L. Vindstad • T. Schott • S. B. Hagen • J. U. Jepsen • L. Kapari • R. A. Ims Received: 22 May 2012 / Accepted: 20 December 2012 / Published online: 12 January 2013 Ó The Author(s) 2013. This article is published with open access at Springerlink.com Abstract Two related issues in studies of biological Several parasitoid groups were shared between two invasions are how quickly the enemy complexes of or more of the geometrids. Total larval parasitism rates invasive species become as species-rich and efficient were similar in all three geometrid species, and as those of native species and how important enemy comparison with published studies on larval parasit- release is for the establishment and spread of invaders. ism in Western Europe suggested that O. brumata and We addressed these issues for the geometrid moths A. aurantiaria do not suffer lower parasitism rates in Operophtera brumata and Agriopis aurantiaria, who our study region than in their native ranges. Our results invaded the coastal mountain birch forest of northern indicate that accumulation of larval parasitoids on Norway by range expansion approximately a century invasive geometrids in coastal mountain birch forest and 15 years ago, respectively. This was done by may reach completion within a few decades to at least comparing larval parasitoid species richness and a century after the invasion, and that establishment and prevalence among the invaders and the native geome- spread of such invaders is unlikely to be facilitated by trid Epirrita autumnata. We found that E. autumnata release from larval parasitism. Our investigations also and O. brumata both hosted seven parasitoid species uncovered a high degree of spatiotemporal synchrony groups, whereas A. aurantiaria hosted only one. between the total larval parasitism rates of O. brumata and A. aurantiaria, suggesting that larval parasitism of different geometrid species in the study system is Electronic supplementary material The online version of this article (doi:10.1007/s10530-012-0393-8) contains governed by some common external factor. supplementary material, which is available to authorized users. Keywords Agriopis Á Altitudinal gradient Á & O. P. L. Vindstad ( ) Á T. Schott Á S. B. Hagen Á Enemy release Á Geometrid Á Invasion Á J. U. Jepsen Á L. Kapari Á R. A. Ims Department of Arctic and Marine Biology, University Parasitoid Á Range expansion of Tromsø, 9037 Tromsø, Norway e-mail: [email protected] Introduction S. B. Hagen Bioforsk Soil and Environment, Svanhovd, Norwegian Institute for Agricultural and Environmental Research, Invasions by alien insect species, facilitated by climate 9925 Svanvik, Norway change or human introduction, are reported from a growing number of ecosystems worldwide. Under- J. U. Jepsen Norwegian Institute for Nature Research, Fram Centre, standing the ecological dynamics of such invasions is 9296 Tromsø, Norway a challenge (Snyder and Evans 2006; Kenis et al. 123 1574 O. P. L. Vindstad et al. 2009; Engelkes and Mills 2011). One fundamental residence times and a native ‘‘reference species’’ question is how rapidly invasive insects recruit within the same system. This may suggest how rapidly effective enemy communities in their invaded ranges. the parasitoid complexes of the invaders are converg- If enemy recruitment is slow, the establishment and ing to a native level, without the potential problems of spread of invaders can potentially be facilitated by comparing different geographical areas. Such within- enemy release and there might be increased risk of range comparisons rely on the assumption that the invaders becoming high-density pests (Torchin et al. parasitoid complexes of the invasive hosts will 2003; Colautti et al. 2004; Torchin and Mitchell 2004; eventually become as species-rich and efficient as Roy et al. 2011). Insects generally suffer heavy the complex of the native host (i.e., that the parasitoid mortality from parasitoids (Godfray 1994; Quicke complexes of the native and invasive hosts are 1997), which therefore make particularly suitable inherently similar). This assumption is not necessarily model systems for testing these ideas. justified, since parasitoid complexes can differ sub- It is typically found that invasive insects (i.e., hosts) stantially even between closely related host species initially suffer lower parasitism rates and are attacked (e.g., Askew 1994). Thus, in order to make inferences by fewer parasitoid species in their invaded than native about parasitoid accumulation and release in invasive ranges (Cornell and Hawkins 1993; Hawkins and hosts as robust as possible, within-range comparisons Cornell 1994; Scho¨nrogge et al. 2006; Menende´z et al. between native and invasive hosts should, ideally, be 2008; Grabenweger et al. 2010). Thus, release from combined with biogeographical comparisons of inva- parasitoids may potentially be important for the sive hosts in their native and invaded ranges. establishment and spread of many invasive insects. In the sub-arctic mountain birch forests (Betula However, it is largely uncertain how long-lasting such pubescens ssp. czerepanovii Orlova) of northern parasitoid release might be. There is evidence that Fennoscandia, a rare opportunity to implement such invasive hosts tend to accumulate additional parasitoid a dual comparative approach is provided by a system species with increasing time since the invasion of three sympatric geometrid moths (Lepidoptera: (Cornell and Hawkins 1993; Hawkins and Cornell Geometridae) with contrasting residence times: 1994), but the speed of this process is not well known. Epirrita autumnata (Bkh.) (Autumnal moth), a native Cornell and Hawkins (1993) and Hawkins and Cornell species; Operophtera brumata (L.) (Winter moth), an (1994) suggested that anywhere between 100 and invader from the south that expanded its range into this 10,000 years may be needed before the parasitoid system about a century ago [first recording near complexes of invasive hosts attain a species richness Tromsø (69°400N) in 1892]; and Agriopis aurantiaria and functionality that is equivalent to the complexes of (Hu¨bner) (Scarce umber moth), another southern native hosts. More precise estimates are difficult to species that invaded by range expansion only about obtain, owing to the extensive timescales involved. 15 years ago [See Jepsen et al. (2011) for details on However, the speed with which an invasive host geometrid invasions in this system]. Both O. brumata accumulates parasitoids can sometimes be assessed by and A. aurantiaria are well known pests of broad- comparing its parasitoid complex between areas leaved trees in their native ranges further south in where it has different residence times (e.g., Scho¨n- Europe (Kenis et al. 2005; Cross et al. 1999), and their rogge et al. 1995, 2006). Unfortunately, the results of parasitoid complexes in these ranges have been such biogeographical comparisons can be difficult to surveyed as part of biological control programs and interpret due to geographical gradients in parasitoid ecological studies. Thus, this three-species geometrid species richness and/or efficiency, which may affect system offers an excellent opportunity to compare the parasitoid complex of an invasive host indepen- parasitism between native and invasive hosts within dently of its residence time (Gro¨bler and Lewis 2008). the invaded range, as well as between invasive hosts in An opportunity to implement an alternative their native and invaded ranges. approach arises when several alien host species have Ongoing monitoring of the three sympatric geo- sequentially invaded a system that was already metrids in the coastal areas of northern Norway has occupied by a taxonomically and ecologically similar captured the invasion of A. aurantiaria in this region native host species. Parasitoid complexes can then be (Jepsen et al. 2011). In the present study, we synthe- compared among invasive hosts with different size the parasitism data gathered throughout the 123 Parasitism in invasive geometrids 1575 monitoring period to map and compare the species- distributions within the study system: E. autumnata composition and prevalence of the larval parasitoid is common in both coastal and continental sections of guilds attacking the three geometrids. Moreover, we the sub-arctic mountain birch system, while the two survey previously published studies on parasitism of invasive geometrids have so far been restricted mainly O. brumata and A. aurantiaria in Western Europe to to the coast [although there is evidence for recent compare the larval parasitoid guilds of these two continental range expansion in O. brumata (Jepsen invaders between their native ranges and our (invaded) et al. 2008)]. In the coastal regions of Troms County, study region in northern Norway. Our results allow us northern Norway, high-density populations of all three to assess how rapidly the larval parasitoid guilds of geometrids occur in sympatry. O. brumata and A. aurantiaria are approaching native levels of species richness and prevalence and to Species-composition and prevalence of larval evaluate the degree to which the establishment and parasitoid guilds in the study region spread of these invaders in the study region might have been facilitated by a release from larval Between 2001 and 2011, we reared parasitoids