Context dependent pollinator limitation Carol C. Horvitz 1, Johan Ehrlén 2 and David Matlaga 1 1 University of Miami, Coral Gables, FL USA 2 Stockholm University, SE Stockholm, SWEDEN Evolutionary Ecology of Multispecific Interactions in Changing Environments ATBC 2007, Morelia, Michoacan, MEXICO

Issue Supplemental pollination = higher plant fitness?

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 oFitness components oReproduction oSurvival oGrowth oPopulation growth rate oStochastic growth rate

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

o N(t+1) = X(t) N(t) o X(t) is a random variable A 1, A 2, A 3 …A K, K environmental states o Transitions and contributions in each environment, a ijβ o λ S = stochastic growth rate Tuljapurkar 1982, 1990 Demographic transitions and fitness in a variable world

In a variable world: sequences, frequencies and new sensitivities o Environmental dynamics o sequences along sample paths o an expected long run stationary distribution o λ s is sensitive to perturbations of means, variances, and transitions in particular environmental states o E δ, E μ, E β and others… o Tuljapurkar et al Am Nat o Horvitz et al Ecology

Lathyrus vernus Long lived perennial forest herb Ranges from central and northern Europe to Siberia Particularly well- studied example

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

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

Field experiment 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:

End of story? NO! o Changing the demographic context can offset costs to λ o In variable environments o the currency for measuring the effects is λ s o 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 Ehrlen and Eriksson 1995, Ecology 69:

Open-pollinated

Ehrlen and Eriksson 1995, Ecology 69: Hand-pollinated

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

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:

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

Demographic context: single constant environment (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 (All simulations that follow use the predator-absent scenario)

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

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

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

Thanks o Rodolfo and John o NSF OPUS o Uppsala University o Stockholm University