Monitoring Movement Into and Through a Newly Planted Rainforest Corridor Using Genetic Analysis of Natal Origin

RESEARCH REPORT doi: 10.1111/j.1442-8903.2009.00490.x Monitoring movement into and through a newly planted rainforest corridor using genetic analysis of natal origin By David Paetkau, Ella Va´zquez-Domıńguez, Nigel I. J. Tucker and Craig Moritz This work was undertaken at a time when David Summary Genetic analysis of individual origins works best with populations that are Paetkau and Ella Vázquez-Domínguez were Post- genetically distinct but which exchange a high rate of immigrants, conditions that don’t nor- doctoral fellows with Craig Moritz at the Depart- mally coexist since immigration acts to prevent the accumulation of genetic differences. We ment of Zoology and Entomology, University of provide empirical results from a newly constructed habitat linkage to illustrate the unique Queensland, St. Lucia 4072, Qld, Australia. David is suitability of such analysis to monitoring the re-establishment of connections between previ- now President and Molecular Artificer with Wild- ously isolated populations. Donaghy’s Corridor links a previously isolated 498 ha fragment of life Genetics International (Box 274, Nelson, BC, rainforest to an adjacent 80 000 ha of intact forest. Starting in the final year of the planting Canada V1L 5P9; Tel +1-250-352-3563; Email: programme that established the corridor, we trapped two species of native small mammals, [email protected]). Ella is a Research Pro- the Bush Rat (Rattus fuscipes) and the Cape York Rat (Rattus leucopus), within and nearby fessor with the Instituto de Ecologıá, Universidad the linkage. We used genetic data from ear clippings to determine which side of the corridor Nacional Autońoma de Me´xico (Ap. Postal 70-275, individual animals originated from, and by comparing this information to trap locations, we Ciudad Universitaria, Me´xico DF 04510, Mexico); identified 16 long-distance movements through the corridor. As genetic analysis of origins and Craig is a Professor at the Museum of Verte- allowed movements to be detected from a single capture event and as it reflected movement brate Zoology, University of California (Berkeley, CA since birth, this approach yielded considerably more data than capture records alone. The 94720-3160, USA). Nigel, at the time coordinating combination of movement and capture records allowed species-specific assessment of corri- the Donahy’s Corridor restoration project, is now dor function, revealing that the use and occupation of the corridor was higher for Bush Rat Director and Principle with Biotropica Australia (PO than for Cape York Rat and was neither symmetrical nor uniform. Long-distance movements Box 866, Malanda, Qld, Australia). The study was through the corridor were most common immediately after habitat restoration, dropping off as undertaken with the goal of developing individual- the reconstructed habitat was colonized. based genetic techniques that would yield practical information on current landscape usage; with Dona- Key words: dispersal, genetic assignment, microsatellite, wildlife corridor. ghy’s Corridor providing a testing ground for these genetic methods. event, may have potential to bridge this balance between genetic drift and migra- Introduction gap in some population systems. tion is near equilibrium, genetic analysis of ispersal is a focal parameter in popula- Genetic assessment of origins has a pro- origins is frustrated by the paradox that Dtion genetics (Wright 1951) and land- ven capacity to assign individuals to their migration limits the very population differ- scape ecology (Wiens 1997) and this population of origin when those popula- entiation which enables the identification intersection has encouraged a search for tions experience little or no ‘migration’ of immigrants (e.g. Manel et al. 2002; Pae- practical management applications of (the geneticist’s term for any movement of tkau et al. 2004); if allele frequencies in genetic movement data. Traditional popu- genes between populations). This capacity two populations have been homogenized lation genetics, which treats populations has been applied to such problems as iden- through gene flow, then the members of as the units of analysis and uses models tifying movement between and coloniza- those populations cannot be distinguished that assume long-term equilibrium, does tion of habitat patches (Eldridge et al. using genetics. not generate the fine-scale, individual- 2001; Berry et al. 2005), identifying the ori- One context in which movement data based, contemporary movement data that gin of hunted animals in the context of have been particularly sought after but dif- are provided by established field tech- management and law enforcement (Manel ficult to obtain (Rosenberg et al. 1997; niques, and that are generally required for et al. 2002; Maudet et al. 2002), or assign- Beier & Noss 1998) is in evaluating the effi- practical assessment of landscape function. ing harvested fish in mixed fisheries to cacy of restored habitat linkages (wildlife Genetic analysis of individual origins (Pae- their breeding stocks (Primmer et al. 1999; corridors) for re-establishing connectivity. tkau et al. 1995; Rannala & Mountain Roques et al. 1999). The approach has Such linkages have been identified as one 1997; Cornuet et al. 1999; Pritchard et al. even documented movement between of the major tools of conservation biology 2000; Guinand et al. 2002), which seeks to conterminous but discretely defined popu- (Tewksbury et al. 2002), but the lack of identify individuals’ place of birth and thus lation fragments in Grizzly Bears (Ursus data surrounding their effectiveness has to detect lifelong movements by individu- arctos;Proctoret al. 2005). However, in been a source of criticism (e.g. Simberloff als that are known from a single capture most population systems, where the et al. 1992). 210 ECOLOGICAL MANAGEMENT & RESTORATION VOL 10 NO 3 DECEMBER 2009 ª 2009 Ecological Society of Australia RESEARCH REPORT From a genetic perspective, the popula- Our goal was to test empirically rainforest-specialist species would not tions on either side of a new habitat link- whether the unique combination of popu- have crossed between Gadgarra and Lake age have been drifting apart in isolation, lation parameters associated with new hab- Barrine since 1931, when the intervening and the role of the linkage is to re-establish itat linkages would provide a practical forest was removed (Tucker 2000a). gene flow. The genetic drift that precedes application of direct genetic analysis of The monitoring program that was habitat restoration creates a scenario with movement. The linkage that we selected applied at Donaghy’s Corridor involved greater initial population differentiation for this purpose (Donaghy’s Corridor) is birds, reptiles, amphibians, invertebrates than would eventually be expected if located in the Wet Tropics World Heritage and mammals (Tucker 2000b). We elected the restoration successfully re-establishes Area of northern Queensland, Australia, to study two species of small, native mam- movement. This unusual and transient and was established between 1995 and mals, Cape York Rat (Rattus leucopus)and combination of relatively high population 1998 along a 1.2-km riparian strip (Tucker Bush Rat (R. fuscipes). These animals were differentiation and – one hopes – relatively 2000a; Fig. 1). The purpose of Donaghy’s selected because they had been captured high-frequency movement could endow Corridor was to reconnect the 498 ha Lake in large enough numbers to enable a genetic assignment methods with the Barrine section of Crater Lakes National genetic study to be undertaken without capacity to detect individual movements. Park with the 80 000 ha of contiguous initiating a new trapping program, and For example, such an approach was used tropical rainforest in the Gadgarra Forest because we expected these forest species to show more or less unidirectional move- section of Wooroonooran National Park. to have been affected by the fragmentation ment into and through a habitat corridor The previously continuous forest in this event. Neither species is noteworthy for its from a rapidly expanding Black Bear region was fragmented during clearing for conservation priority. (U. americanus)population(Dixonet al. agricultural settlement in the early 1900s, The study species are difficult to distin- 2006). and it was our expectation that many guish in the field, but one or both can be found in the wet eucalyptus forest that occurs adjacent to the rainforest, although they are more abundant in the latter (Wil- liams et al. 2002). It has been suggested that the Cape York Rat is more tolerant of forest edge than its congener, and that small forest fragments tend to contain only one or the other of these two species (Lau- rance 1994). Our laboratory analysis made use of highly variable microsatellite markers, and the statistical interpretation of the resulting data employed several of the rapidly evolv- ing methods that use genetic data to draw inference about individual origins. Methods Donaghy’s Corridor Donaghy’s Corridor was established by planting approximately 18 000 rainforest plants (103 species) in four blocks, one block planted each year between 1995 and 1998 (Tucker 2000a,b; Tucker & Simmons 2009; Fig. 1). The linkage varies between 70 m and 120 m in width, and is bounded on either side by a 15-m windbreak ⁄ agro- forestry zone of Hoop Pine (Araucaria Figure 1. Donaghy’s Corridor. This habitat linkage was planted in four sections between 1995 ). The 1995 planting and 1998. It follows a natural stream

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