Invasive Species in Tropical Ecosystems: Patterns, Impacts and Needs Susan Cordell Institute of Pacific Islands Forestry USDA, Forest Service USDA-FS R&D Workshop State of Science for Non-native Invasive Species December 8-11, 2015 Phoenix, AZ
Tropical forests: Background contain more that ½ of the worlds biodiversity play an increasingly important role is carbon storage, climate mitigation, and provisioning of ecosystem services are expected to suffer extraordinarily from global change ~100 million ha converted to farmland between 1980-2012* 24% intact 46% fragmented 30 % degraded Invasion debt exists and is likely increasing** *Gibbs et al 2010, Hansen et al 2013 **Simberloff 2014
Hawaii and Pacific Islands Low species diversity but high endemism (e.g., 90% of plants and 98% of insects in Hawai`i). Island endemics have small populations with limited distributions. Over 476 internationally recognized T&E species.
Natural dispersal over 4.1 million years accounts for 272 introductions and gave rise to the Hawaiian flora FLOWERING PLANTS Species 1304 Endemic (90%) 1160 Extinct 106 T/E 282 FERNS Species 150 Endemic (70%) 105 Clermontia hawaiiensis (Lobeliaceae)
HAWAIIAN PLANT INTRODUCTIONS Polynesians (300 AD): 32 species naturalized Post Capt. Cook (1778): >4600 introductions 1100 naturalized >100 invasive
What we know 13,168 or 3.9 % of the extant global vascular flora have become naturalized somewhere else as a result of human activity* Pacific Islands show the fastest increase with respect to land area Continents with the largest tropical regions have fewer naturalized alien species then temperate ones *M van Kleunen et al. Nature 000, 1-4 (2015) doi:10.1038/nature14910
We also know A meta analysis of trait differences between invasive and non invasive plant species No single invasion hypothesis or trait difference explains invasions in general Most likely mechanisms work synergistically to promote invasion From van Kluenen et al 2010 Ecology Letters Volume 13, Issue 2, pages 235-245
Axis 2: 15% of the variance Hawaiian lowland forest example Cumulative variance explained: 46% 15 natives (in blue) 16 non-natives (in gold) 13 invasives (in red) 3. Foliar P 2. Stature (field height) 1. Seed mass, *PCA developed using quartiles 2. Foliar N Axis 1: 31% of the variance 1. Foliar C:N 3. LMA
And Invasive species can be classified by the type and degree of their impact Impact scheme of the Global Invasive Species Database, implemented by the IUCN Species Survival Commission (SSC) Invasive Species Specialist Group. Blackburn TM, Essl F, Evans T, Hulme PE, Jeschke JM, et al. (2014) A Unified Classification of Alien Species Based on the Magnitude of their Environmental Impacts. PLoS Biol 12(5): e1001850. doi:10.1371/journal.pbio.1001850
What we don t know about invasive species roles/impacts Interaction with climate change Dependent on species and ecosystem type - see Loarie SR, Duffy PB, Hamilton H, Asner GP, Field CB, Ackerly DD (2009) The velocity of climate change. Nature 462:1052-1055 Trophic interactions Invasive plants had reducing or neutral effects but data is limited - see Schirmel J, Bundschuh M, Entling MH, Kowarik I, Buchholz S (2015) Impacts of invasive plants on resident animals across ecosystems, taxa, and feeding types: A global assessment. Global Change Biology Long term dynamics The effects of invasive plants will increase, decrease, or be maintained - see Flory SL, D Antonio CM (2015) Taking the long view on the ecological effects of plant invasions. American Journal of Botany 102:817-818
More on long term dynamics Short term results don t always equate to long term outcomes see Cordell et al. (in Press).Quandaries of a decade-long restoration experiment trying to reduce invasive species: Beat them, join them, give up, or start over? Restoration Ecology
Needs Whole ecosystem approach experimental manipulations in natural and human modified systems (see Fayle TM, Turner EC, Basset Y, Ewers RM, Reynolds G, Novotny V (2015) Wholeecosystem experimental manipulations of tropical forests. Trends in Ecology & Evolution) Manipulations: Weather and climate Key ecological groups Water and nutrients Simulations of disturbance Restoration
More Needs Novel approaches to reduce invasive species impacts Functional trait based restoration (see - Drenovsky RE, Grewell BJ, D'Antonio CM, Funk JL, James JJ, Molinari N, Parker IM, Richards CL (2012) A functional trait perspective on plant invasion. Annals of Botany; Ostertag R, Warman L, Cordell S, Vitousek PM (2015) Using plant functional traits to restore Hawaiian rainforest. Journal of Applied Ecology) Expanded genetic and bio-control tools (see- Webber BL, Raghu S, Edwards OR (2015) Opinion: Is CRISPR-based gene drive a biocontrol silver bullet or global conservation threat? Proceedings of the National Academy of Sciences 112:10565-10567) Plant pathogens to manage invasions (see - Flory SL, Clay K (2013) Pathogen accumulation and long-term dynamics of plant invasions. Journal of Ecology 101:607-613)
More on trait based approaches Pro-bowl for ecologists: How to pick a winning team of plants to restore Hawaii s lowland wet forests Design and create multi-use, self-sustaining hybrid ecosystems with an experimental design that: addresses management needs in Hawaii and Pacific provides an approach that is transferable to other ecosystems (functional traits) tests fundamental questions about community assembly
Conclusions Research on invasive species in the tropics should be a priority. Investments in long term and whole ecosystem approaches should be emphasized. Novel approaches should be explored to reduce invasive species impacts.
Mahalo