Journal of Tropical Ecology (2017) 33:205–212. © Cambridge University Press 2017 doi:10.1017/S026646741700013X Invasive Syzygium jambos trees in Puerto Rico: no refuge from guava rust Erin Burman 1,2 , James D. Ackerman 3, ∗ and Raymond L. Tremblay 4,5 1 El Verde Field Station, HC-05 Box 8974, R´ ıo Grande PR 00745–9601, USA 2 Department of Biology, Rhodes College, Box 2338, 2000 N. Parkway, Memphis TN 38112, USA 3 Department of Biology, University of Puerto Rico, P.O. Box 23360, San Juan PR 00931–3360, USA 4 Department of Biology, University of Puerto Rico, P.O. Box 860, Humacao PR 00791, USA 5 Center for Applied Tropical Ecology and Conservation, University of Puerto Rico, P.O. Box 23360, San Juan PR 00931–3360, USA (Received 17 February 2017; revised 7 May 2017; accepted 10 May 2017) Abstract: Biological invasions can have negative consequences for resident biota, particularly when disease-causing organisms are involved. Austropuccinia psidii, or guava rust, has rapidly spread through the tropics affecting both native and non-native Myrtaceae. In Puerto Rico, the rust has become common on Syzygium jambos, an invasive tree native to South-East Asia. What are the drivers of infection, and do refugia exist across a heterogeneous landscape? We address these questions using species distribution modelling and beta regressions. The realized and potential distribution of Syzygium jambos is extensive. The model produced an AUC of 0.88, with land-use categories and precipitation accounting for 61.1% of the variation. Predictability of S. jambos is highest in disturbed habitats, especially in mountainous regions with high precipitation. All 101 trees surveyed and measured across Puerto Rico showed signs of infection to varying extents. Infection severity was consistently associated with annual mean temperature in all top beta regression models, but was also commonly associated with tree size and precipitation variables. We found no safe sites for S. jambos. Many trees were extremely unhealthy and some were dead, suggesting that S. jambos may soon become extinct on the island or reduced to persistent stump sprouts. Native vegetation may benefit from the local demise of S. jambos. While the rust has not jumped to native Myrtaceae, vigilance is required, as host-shifts have occurred in other tropical regions. Key Words: guava rust, invasional collapse, invasive trees, island invasions, pathogen invasion, Puccinia, Syzygium, tropical forest, tree disease INTRODUCTION In native habitats, plant diseases are common, but rarely do they form epidemics with devastating consequences to host populations (Burdon 1987, Gilbert 2002, Mel´ endez & Ackerman 1993). However, where disease-causing organisms have invaded novel environments, epidemics can be pervasive with severe outcomes for host species and the ecosystems in which they reside (Gessler et al. 2011, Huang et al. 1998, Webber 2004). Under those circumstances, spread of diseases is dependent on a number of factors, such as host life-history stage, propagule pressure, environmental conditions and spatial heterogeneity (Gilbert et al. 1994, Meentemeyer et al. 2012, Plantegenest et al. 2007). Recent outbreaks of Austropuccinia psidii (G. Winter) Beenken, known as myrtle, pimento or guava rust, ∗ Corresponding author. Email: ackerman.upr@gmail.com have had severe consequences to species of Myrtaceae throughout the tropics and subtropics, including regions where the rust has not been previously reported (Coates- Beckford & Tennant 2013, Rayamajhi et al. 2013, Uchida & Loope 2009). The potential for further invasions by A. psidii is high. Distribution modelling using climatic variables suggests that its potential distribution in the Neotropics exceeds its known range (Booth et al. 2000). Furthermore, the rust is genetically diverse, and different genotypes often have different sets of host species. Consequently, infection dynamics differ among regions depending on which of the genotypes are present (MacLachlan 1938, Ross-Davis et al. 2014). On the Caribbean island of Puerto Rico, the A. psidii outbreak began in 2006 and continues to the present day, thus far only infecting Syzygium jambos (L.) Alston, probably reflecting a different strain than that initially reported for the island (Arthur 1915). Other than these observations, little is known of the drivers of guava https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S026646741700013X Downloaded from https:/www.cambridge.org/core. University of Puerto Rico -- Rio Piedras, on 16 Jun 2017 at 14:28:01, subject to the Cambridge Core terms of use, available at