tropical forests and its biodiversity implications: What do we - PowerPoint PPT Presentation

Trophic downgrading in tropical forests and its biodiversity implications: What do we know? Nicole L. Michel, Ph.D. School of Environment & Sustainability University of Saskatchewan

Trophic cascades in tropical forests?  Predators keep the world green (Hairston et al. 1960)  Diversity, redundancy, weak links preclude cascades in tropical forests? (e.g., Strong 1992, Polis & Strong 1996) Photos by Nicole Michel, Smithsonian Wild 1960s

Janzen-Connell Hypothesis Photos by The Agouti Enterprise, 1970s Nicole Michel, Phylum Arthropoda Wikispaces

Tropical vertebrate community changes  Barro Colorado Island  Large predators, herbivores and frugivores declined, small mammals increased 1932-1937 (Enders 1939)  Abundant small- and mid-sized mammals? (Eisenberg & Thorington 1979, Glanz 1982)  Amazon  Large mammals defaunated (Emmons 1984) Photo from Smithsonian Wild 1930s - 1980s

Early trophic downgrading  Extinction of gomphotheres and other megafauna 10,000 years ago altered dispersal, distribution of large-seeded trees, e.g., Jicaro ( Crescentia alata ) (Janzen & Martin 1982)  Livestock compensate? Photos by Cody H., Travis S. 1980s

Vertebrates reduce seed, seedling survival  ~3x higher seed predation on protected BCI (DeSteven & Putz 1984)  Seedling density ~4x greater, and seedling survival, growth, and success greater on hunted mainland ( Sork 1987)  La Selva: 82% “seedlings” damaged, ~50% by vertebrates (Clark & Clark 1989) Photo from Plantacion Edelman 1980s

Do tropical apex predators regulate terrestrial herbivores & frugivores?  Wolves regulate  Do big things run the ungulates, e.g., moose on world in tropical forests? ( Terborgh 1988) Isle Royale (Peterson et al. 1984) Photos by Pete Dawson, Dennis Matheson 1980s

Trophic cascade on Barro Colorado Island?  Frugivores released from predation, reducing large-seeded plant recruitment? (Terborgh 1992)  Seed predation, seedling recruitment similar at BCI and Cocha Cashu ( Terborgh & Wright 1994)  BCI frugivore densities overestimated, felids do not limit frugivores long-term (Wright et al. 1994)  Felids incapable of limiting frugivores on BCI (Leigh 1999)  Felids do not maintain frugivores below famine-susceptible levels (Wright et al. 1999) …Yet the question of “just how different is BCI” continues today 1990s

The Empty Forest  “ We must not let a forest full of trees fool us into believing that all is well. Many of these forests are ‘living dead’ (Janzen 1988), and, although satellites passing overhead may reassuringly register them as forest, they are empty of much of the faunal richness valued by humans. An empty forest is a doomed forest .” (Redford 1992) Photos by Rodolfo Dirzo, Nicole Michel 1990s

Defaunation consequences context-dependent Effects on seed and seedling survival, recruitment, and density depend on plant traits, and consumer communities:  Low seed predation, low herbivory, high seedling density in hunted Los Tuxtlas plots (Dirzo & Miranda 1990, 1991)  100% seed predation, high herbivory, low seedling density on small Lago Gatun islands (Asquith et al. 1997) Photos by Rodolfo Dirzo, Nicole Michel 1990s

Primacy of predation or dispersal?  Janzen-Connell: mixed evidence for distance-dependent mortality, negative density-dependence not supported (Schupp 1992, Terborgh & Wright 1994)  Frugivores may predate 50-90%+ of seed crop  Assuming J-C effects, dispersal and escape by even 1-2% of seeds may be more important (Brewer et al. 1997) Photos by Rodolfo Dirzo, Nicole Michel 1990s

A new millennium  Plethora of defaunation studies  Special issues in Biotropica (2007) and Biological Conservation (2013)  Existing knowledge honed, new patterns emerging Photo by Robert Hruzek 2000 - today

The bushmeat crisis expands  22 of 30 large vertebrates declined by up to 75% across 13 heavily-hunted Amazonian sites (Peres & Palacios 2007)  Primate abundance 80% lower at hunted site outside Manu NP ( Nuñez-Iturri & Howe 2007)  Majority of tropical nature reserves may be Empty Forests ( Harrison 2011) Photos by Bongo Vongo, Paul Rosolie 2000 - today

Primacy of predation or dispersal context- dependent Relative importance of predation versus dispersal contingent on, e.g.:  Plant traits, e.g., seed size, toughness  Herbivore / frugivore body size  Abiotic conditions Photo by Christian Ziegler 2000 - today

Defaunation effects on large-seeded plants driven by frugivore community  Large-seeded plants suffer from loss of dispersers across the Amazon, Atlantic Forest, southern Mexico, and Australia (Corlett 2007, Cramer et al. 2007, Nuñez-Iturri & Howe 2007, Peres & Palacios 2007, Donatti et al. 2009, Moran et al. 2009, Melo et al. 2010)  Large-seeded plants benefit from reduced seed predation in Los Tuxtlas, Costa Rica, and Panama (Dirzo et al. 2007, Wright et al. 2000, 2007; Hanson and Brunsfeld 2006) Photo by Reinaldo Aguilar 2000 - today

Defaunation consequences scale with frugivore body size?  Smaller-bodied seed dispersers (e.g., rodents) do not fully compensate for either mid-sized or large dispersers (Galetti et al. 2006, 2010, Kurten 2013)  Megafauna have larger total impacts: consume and disperse small-large seeds, trampling. Ecosystem engineers? (Wang et al. 2007, Johnson 2009, Vanthomme et al. 2010, Dunham 2008, 2011, Campos-Arceiz & Blake 2012, Jothish 2013) Photo from Safari Partners 2000 - today

Defaunation consequences contingent on abiotic conditions?  Herbivore effects on plant communities strongest with low rainfall, low productivity, high nutrient availability (Pringle et al. 2007, Asner et al. 2009, Goheen et al. 2013) Image from Asner et al. 2009, PNAS 2000 - today

Defaunation consistently reduces diversity  Regardless of biotic or abiotic context, defaunation reduces seedling diversity (Wright et al. 2000, 2007, Wright & Duber 2001, Wright 2010)  Negative density-dependence may allow declining tree species to rebound after forest is protected, seed dispersers and predators return (Muller-Landau 2007) Photo by Nicole Michel 2000 - today

Janzen-Connell  Results – especially for density-dependence – are mixed, hypothesis difficult to falsify? (Carson et al. 2008)  Meta-analysis of 40 studies: no distance effects (Hyatt et al. 2003)  Distance, not density, effects in seedlings at Cocha Cashu , distance and density effects in saplings (Swamy & Terborgh 2010)  Distance effects important, but limited rain of dispersed seeds precludes density effects at CC (Terborgh et al. 2011, Terborgh 2013)  Monkey gut passage more important than J-C effects in Amazon (Levi & Peres 2013) Yet Janzen-Connell “essentially correct” (Terborgh 2013)  Image from The Agouti Enterprise 2000 - today

“Ecological Meltdown”  While less common, apex predator loss, restricted hunting, ample food may facilitate short- or long-term herbivore, frugivore population growth  Howler monkeys, leaf-cutter ants at Lago Guri, Venezuela (Terborgh et al. 1999, 2001, 2006)  Bearded pigs, primates, rodents at Ganung Palung National Park, Borneo (Curran et al. 1999, Curran & Leighton 2000)  Wild pigs at Pasoh Forest Reserve, Malaysia (Ickes 2001, Ickes et al. 2001) Photos by Nicole Michel, John Terborgh 2000 - today

Collared peccaries ( Pecari tajacu ) Peccary Density 14 (per km 2 ) Site (number of pictures 100 days-1) 12 Relative Abundance Index 3.0 1 Gigante 10 8 Barro Colorado 6.7 - 12.4 2 6 Amazon unhunted 6.6 + 1.3 3 4 2 La Selva ? 0 Gigante BCI La Selva 1 Wright et al. 2000; 2 Eisenberg and Thorington 1973, Glanz 1982, Wright et Photo by Geoff Gallice al. 1994, 2000; 3 Peres & Palacios 2007; RAI: Hurtado & Jansen 2012, TEAM

La Selva Biological Station LRR -0.53 -0.20 -0.20 25 A A A ** Mammals present 20 Mammals excluded Percent liana cover 15 10 5 0 BCI Gigante La Selva Photos by Nicole Michel 2000 - today

Cascading consequences of altered consumer communities  Lago Guri: howler monkeys increase bird density, richness (Feeley & Terborgh 2008)  La Selva: near-extirpated understory insectivorous birds forage in liana tangles reduced by peccaries (Michel 2012, Michel et al., in revision)  La Selva: greater litter herpetofauna abundance in presence of peccaries (Reider et al. 2013)  Defaunation reduces dung beetle richness (Nichols et al. 2009) Photo by Dominic Sherony 2000 - today

Research needs for the next 50 (1000?) years  Improve predictions of defaunation consequences based on plant traits, frugivore communities  Are consumer effects additive, interactive, redundant?  Is trophic downgrading stronger in the Afrotropics?  Will density-dependence compensate for reduced seedling diversity, maintaining canopy tree diversity?  Identify keystone seed dispersers, predators. In what range of abundance do they maintain plant diversity?  Defaunation impacts on carbon sequestration?  … Next 50+ years