ECOSYSTEM ECOLOGY - ORIGINAL PAPER Improved recruitment of a lemur-dispersed tree in Malagasy dry forests after the demise of vertebrates in forest fragments K. H. Dausmann Æ J. Glos Æ K. E. Linsenmair Æ J. U. Ganzhorn Received: 3 September 2007 / Accepted: 12 May 2008 / Published online: 4 June 2008 Ó Springer-Verlag 2008 Abstract The objective of this study was to examine how the processes of seed dispersal and seed predation were altered in forest fragments of the dry forest of Madagascar, where the usual seed dispersers and vertebrate seed pre- dators were absent, using a lemur-dispersed tree species (Strychnos madagascariensis; Loganiaceae) as an example. We then assessed how the changes in vertebrate commu- nity composition alter the regeneration pattern and establishment of this tree species and thus, ultimately, the species composition of the forest fragments. By using size- selective exclosures, data from forest fragments were compared with results from continuous forest where ver- tebrate dispersers and predators were abundant. Visits to the exclosures by mammalian seed predators were moni- tored with hair traps. In the continuous forest up to 100% of the seeds were removed within the 7 days of the experi- ments. A substantial proportion of them was lost to seed predation by native rodents. In contrast, practically no predation took place in the forest fragments and almost all seeds removed were dispersed into the safety of ant nests by Aphaenogaster swammerdami, which improves chances of seedling establishment. In congruence with these find- ings, the abundance of S. madagascariensis in the forest fragments exceeded that of the continuous forest. Thus, the lack of vertebrate seed dispersers in these forest fragments did not lead to a decline in regeneration of this animal- dispersed tree species as would have been expected, but rather was counterbalanced by the concomitant demise of vertebrate seed predators and an increased activity of ants taking over the role of seed dispersers, and possibly even out-doing the original candidates. This study provides an example of a native vertebrate-dispersed species apparently profiting from fragmentation due to flexible animal-plant interactions in different facets, possibly resulting in an impoverished tree species community. Keywords Seed dispersal and predation Á Fragmentation Á Regeneration Á Exclosure experiments Á Madagascar Introduction Fragmentation is considered to be one of the most impor- tant threats to biodiversity in tropical forest ecosystems (Smith and Hellmann 2002). While early studies concen- trated on the effect of habitat loss based on the hypotheses of island biogeography (reviewed by Laurance and Bier- regaard 1997), recent approaches emphasize synergistic effects in fragmented landscapes that have negative effects on native populations beyond the effect of area loss (Fahrig 2003). Plant and animal species that inhabit tropical forests have developed complex ecological interactions with one another over millions of years, and have thereby shaped these forests. There is a sudden interruption of these Communicated by Jacqui Shykoff. Electronic supplementary material The online version of this article (doi:10.1007/s00442-008-1070-6) contains supplementary material, which is available to authorized users. K. H. Dausmann Á K. E. Linsenmair Department of Animal Ecology and Tropical Biology, Biozentrum, Am Hubland, Julius-Maximilians-University Wu ¨rzburg, 97074 Wu ¨rzburg, Germany K. H. Dausmann (&) Á J. Glos Á J. U. Ganzhorn Department of Animal Ecology and Conservation, Biozentrum Grindel, University of Hamburg, Martin-Luther-King-Platz 3, 20146 Hamburg, Germany e-mail: kathrin.dausmann@uni-hamburg.de 123 Oecologia (2008) 157:307–316 DOI 10.1007/s00442-008-1070-6