Context dependent pollinator limitation Evolutionary Ecology of Multispecific Interactions in Changing Environments ATBC 2007, Morelia, Michoacan, MEXICO Context dependent pollinator limitation Carol C. Horvitz1, Johan Ehrlén2 and David Matlaga1 1University of Miami, Coral Gables, FL 33124 USA 2Stockholm University, SE-106 91 Stockholm, SWEDEN

Supplemental pollination = higher plant fitness? Issue Supplemental pollination = higher plant fitness?

Demographic, biotic, abiotic variability in the environment Contexts Demographic, biotic, abiotic variability in the environment Ecological, evolutionary and conservation consequences of pollen limitation e.g. Ashman et al. 2004

Candidate currencies for measuring fitness Fitness components Reproduction Survival Growth Population growth rate Stochastic growth rate

Demographic transitions and fitness in a constant world N(t+1) = A N(t) A is a population projection matrix Transitions and contributions between stages, aij = fitness components λ = population growth rate

Demographic transitions and fitness in a variable world N(t+1) = X(t) N(t) X(t) is a random variable A1, A2, A3…AK , K environmental states Transitions and contributions in each environment, aijβ λS = stochastic growth rate Tuljapurkar 1982, 1990

In a variable world: sequences, frequencies and new sensitivities Environmental dynamics sequences along sample paths an expected long run stationary distribution λs is sensitive to perturbations of means, variances, and transitions in particular environmental states Eδ, Eμ, Eβ and others… Tuljapurkar et al. 2003 Am Nat Horvitz et al. 2005 Ecology

Lathyrus vernus Long lived perennial forest herb Ranges from central and northern Europe to Siberia Particularly well-studied example http://caliban.mpiz-koeln.mpg.de/~stueber/thome/band3/tafel_135_small.jpg

not exactly tropical… Deciduous forest Quercus, Fraxinus, Betula Tullgarnsnäset SW of Stockholm 58º6’ N, 17º4’ E Deciduous forest Quercus, Fraxinus, Betula

Bruchus (seed predator) Demographic costs of seeds and beetles Players Bombus (pollinator) Bruchus (seed predator) Demographic costs of seeds and beetles

Field experiment λ was negatively affected Supplemental pollen increased seed set within the year BUT Next year’s flower production and growth reduced λ was negatively affected Ehrlen and Eriksson 1995, Ecology 69:652-656

End of story? NO! Changing the demographic context can offset costs to λ In variable environments the currency for measuring the effects is λs frequency and sequence of high pollination years relative to other kinds of years determine outcome

Stages seeds seedlings small intermediate large vegetative large flowering dormant rhizome http://www.paghat.com/vetch.html Ehrlen and Eriksson 1995, Ecology 69:652-656

Open-pollinated Ehrlen and Eriksson 1995, Ecology 69:652-656

Hand-pollinated Ehrlen and Eriksson 1995, Ecology 69:652-656

Costs to fates of large flowering plants and to λ More seeds Shrink Go Dormant Flower Less Data in Ehrlen and Eriksson 1995, Ecology 69:652-656

But 53% of seeds had been lost to beetles (both open and hand pollinated plants) Observed seeds = “Gross Seeds” - Beetles Beetles cost as much as seeds… Observed fates really for “Gross Seeds” Data in Ehrlen and Eriksson 1995, Ecology 69:652-656

Elimination of seed predators lessens negative effect on λ Data in Ehrlen and Eriksson 1995, Ecology 69:652-656

Demographic context: single constant environment Using λ to measure fitness Δ Seed survival Δ Germination Δ Seedling survival Using λs to measure fitness Some years High Pollination Some years Low Pollination High germination year added Δ Frequency Δ Sequence (All simulations that follow use the predator-absent scenario)

Higher seed survival can compensate for cost

Higher germination can compensate for cost

Higher seedling survival can NOT compensate for cost

Demographic context: multiple environmental states Using λ to measure fitness Δ Seed survival Δ Germination Δ Seedling survival Using λs to measure fitness Some years High Pollination Some years Low Pollination High germination year added Δ Frequency Δ Sequence (All simulations that follow use the predator-absent scenario)

2-state model for variable environment Probability rules that generate environmental sequences Columns sum to 1 Dot size indicates probability Color coded for environmental state to which the system transitions Env at time t+1 Env at time t

2-state IID models Increasing probability of going to a high pollination year

Variable environments: Increasing frequency of high pollination year decreases fitness

Focus on world with 70% high, 30% low pollination What is the outcome of adding some high germination years among the low pollination years?

Now there are three environments Low pollination (as before) High pollination (as before) Low pollination accompanied by High (9x) germination λ = 1.063 λ = 1.055 λ = 1.157

3-state IID models High germination any time

3-state Markov models High germination only after high pollination

Variable environments: increasing frequency of high germination years increases fitness Sequence matters

Changing the demographic context can offset costs to λ Conclusions Changing the demographic context can offset costs to λ In variable environments the currency for measuring the effects is λs frequency and sequence of high pollination years relative to other kinds of years determine outcome

Thanks Rodolfo and John 2006-08 NSF OPUS Uppsala University Stockholm University