Ecological Effects of Leaf Mining Plant Performance and Trophic Dynamics Diane Wagner LTER Symposium February 2014
Acknowledgements Collaborators Pat Doak Knut Kielland Tom Clausen Linda Defoliart Jenny Schneiderheinze Graduate students Brian Allman Brent Mortensen Jonathon Newman Adam Watson Brian Young 2
Local leaf miner and chewers densities on deciduous trees 250 Number insects m -2 200 150 100 50 0 Leaf miners External chewers 1975 1980 1985 1990 1995 2000 2005 2010 Year BC LTER: Defoliating Insect Population Levels Werner & Kruse
1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 Area infested (ha) Major leaf miner outbreaks across Alaska 350,000 300,000 250,000 200,000 150,000 100,000 50,000 0 Aspen leaf miner Willow leaf blotch miner Aerial Insect Detection Survey USFS
Outline Why did ALM outbreak last so long? What caused the end of the ALM outbreak? How does aspen leaf miner (ALM) affect aspen performance? New experiment: Long term ecosystem consequences of insect herbivory, mammalian browsing, and their interaction
Aspen leaf miner moth (Phyllocnistis populiella) North American native One generation per year Larvae consume epidermal cell layer Restricted to one side of a single leaf until adulthood Adults emerge in June, overwinter under spruce 7
Why did the ALM outbreak last so long? High plant tolerance of herbivory Nutrient stores Insect behavior Larvae unable to attack foliage produced late in growing season (one generation, larvae immobile) Aggression towards conspecifics prevents decimation of food supply
Pupal mass (mg) Probability of individual survival Estimated number surviving Percent of leaf surface mined (a) 80 Competition 60 40 14 12 20 10 0 8 (b) 0.56 Eggs per leaf 0.44 2 0.3 0 0.2 0.1 (c) 1 2006 2007 max n survivors 2008 2009 2010 2011 0.0 Pupal mass of survivors (mg) 2012 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Leaf area mined (%) 70 60 50 40 30 20 10 0 2006 2007 2008 2009 2010 2011 2012 0.8 0.6 0.4 0.2 0 0 5 10 15 Initial number of larvae Initial larvae per leaf Doak & Wagner in review
Pupal mass (mg) Probability of individual survival Estimated number surviving Percent of leaf surface mined (a) (b) (c) 80 60 Eggs per leaf 40 14 12 20 10 0 8 0.56 0.44 2 0.3 0 0.2 0.1 2006 2007 max n survivors 2008 2009 2010 2011 0.0 Pupal mass of survivors (mg) 1 0.8 0.6 0.4 0.2 Competition 2012 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Leaf area mined (%) 70 60 50 40 30 20 10 0 2006 2007 2008 2009 2010 2011 2012 Intense interference competition: Prevents food limitation Allows some larvae to survive leaf overpopulation Preserves leaf function 0 0 5 10 15 Initial number of larvae Initial larvae per leaf Doak & Wagner in review
What ended the outbreak? Phenological mis-match Adult overwintering survival Egg mortality Larval parasitism Larval and pupal predation (ants, birds) Larval and pupal mortality unassigned (other predators, pathogens, plant quality)
What ended the outbreak? Phenological mis-match Adult overwintering survival Egg mortality Larval parasitism Larval and pupal predation (ants, birds) Larval and pupal mortality unassigned (other predators, pathogens, plant quality)
Survivors per leaf 1.0 0.8 0.6 0.4 0.2 What ended the outbreak? 0.0 2006 2007 2008 2009 2010 2011 2012 2013 Percent of individuals 100 80 60 40 20 0 2006 2007 2008 2009 2010 2011 2012 Dead in leaf Removed Parasitized Survived Indirect effect of WLBM increase? Doak & Wagner in review
How does leaf mining affect aspen Methodology performance? Experimental suppression of leaf miner density on aspen < 2m 2 sites: Bonanza Creek and Ester Dome; mixed stands 7 years 15
How does leaf mining affect aspen performance? Mortality No effect of leaf miner suppression Growth and size Strong effects
Effects of leaf mining across 7 years Height (cm) 160 140 120 100 80 60 40 Insecticide Control Diameter at 20 cm (mm) 20 18 16 14 12 10 8 20 2005 2012 6 2005 2012 Implications for browsing, competition Wagner & Doak 2013
Mechanisms of ALM-caused aspen decline Early leaf abscission (Wagner et al. 2008) Leaf mining reduces photosynthesis by disrupting stomatal function (Wagner et al. 2008) Mining disrupts water balance (unpubl.) Mining induces ineffectual defenses Phenolic glycosides (Young et al. 2007) Extrafloral nectar (Newman & Wagner 2013) Both increase costs
Willow leaf blotch miner (Micrurapteryx salicifoliella)
One generation Multiple Salix hosts Willow leaf blotch miner (Micrurapteryx salicifoliella) Larvae consume mesophyll Mobile will move to new leaves within plant
Wide variation in susceptibility among willow species % Leaf mining 100 80 60 40 20 0 2010 2011 MYRT ALAX GLAU BEBB NIPH PSMY ARBU W illow species INTE PULC LASI PSMO
Questions What are the individual and combined effects of invertebrate and vertebrate herbivores on the early successional plant community & ecosystem? Do invertebrate and vertebrate herbivore interact indirectly through effects on plant: Production Plant chemistry / palatability E.g. Summer insect leaf herbivory may affect availability or palatability of species preferred by mammals in winter
Experiment: Impact of, and interactions between, invertebrate & vertebrate herbivores Started spring 2012; ~10 year duration Invertebrate suppression (insecticide) x exclusion of moose/hares (fencing) Dependent variables: Willow herbivory, browse, litter production, chemistry Community composition Soil nutrients, decomposition Tanana River
Impact of, and interactions between, insect & vertebrate herbivores Preliminary results Suppressing insect herbivory increased woody browse production (~ 50% in 2012) No effect of insect suppression on browse C/N, tannin PPC No effect of insect suppression on browsing removal No notable changes in community composition to date
Summary Why did ALM outbreak last so long? Strong interference competition reduced food limitation and plant damage What caused the end of the ALM outbreak? Juvenile mortality by biotic agent How does aspen leaf miner (ALM) affect plant performance? Weak effects on outright mortality; strong negative effects on plant size New experiment: Long term consequences of invertebrate herbivory, vertebrate browsing, and their interaction Underway, more to come