Predator identity and prey size-structure shape immediate and cumulative costs of
risk-induced early hatching
B. Willink, M.S. Palmer, T. Landberg, J.R. Vonesh and K.M. Warkentin
Appendix 1: Model simplification
Table A1. Stepwise model simplification by a Akaike Information Criterion (AIC)
algorithm used to obtain minimal adequate models for tadpole survivorship, growth and
final length in our experimental design. At each step all possible simplifications were tested
but only the simplification with the lowest AIC score is shown.
Experiment
1: 24 h
Model
AIC
Saturated model
Survivorship Survivorship ~ Predator * Hatching age * Age structure
523.59
– Predator : Hatching age : Age structure
518.64
– Predator : Age structure
515.83
– Hatching age : Age structure
514.57
– Age structure
513.16
– Predator : Hatching age
544.20
Best model
Survivorship ~ Predator * Hatching age
513.16
1: 24 h
Saturated model
Growth
Growth ~ Predator * Hatching age * Age structure * Initial length -315.95
– Predator : Hatching age : Age structure : Initial length
-319.59
– Predator : Hatching age : Age structure
-322.49
– Hatch : Age structure : Initial length
-324.49
– Predator : Age structure : Initial length
-324.55
– Predator : Age structure
-327.31
– Age structure : Initial length
-328.94
– Hatch : Age structure
-330.45
– Age structure
-332.37
– Predator : Hatch : Initial length
-320.15
Best model
Growth ~ Predator * Hatching age * Initial length
1: 72 h
-332.37
Saturated model
Survivorship Survivorship ~ Predator * Hatching age
317.07
– Predator : Hatching age
350.02
Best model
Survivorship ~ Predator * Hatching age
317.07
1: 72 h
Saturated model
Growth
Growth ~ Predator * Hatching age * Initial length
-56.79
– Predator : Hatching age : Initial length
-59.94
– Hatching age : Initial length
-61.59
– Predator : Hatching age
-63.32
– Predator : Initial length
-66.12
– Initial length
-66.84
– Hatching age
-55.93
Best model
Growth ~ Predator + Hatching age
-66.84
Appendix 2: Effect of initial length on tadpole growth
Figure A1. Effects of initial length on tadpole growth over their first 24 h in the water.
Regression lines indicate where the slopes are significantly different from cero (α = 0.05).
The effect of initial length on tadpole growth differed among predatory environments and
hatching age classes. In environments with relatively strong predation (belostomatid and
aeshnid predator), smaller tadpoles grew faster within each age class. In environments with
relatively low predation risk initial size affected growth in only one hatching age class.
Appendix 3: Behavioral observations
We recorded tadpole activity – i.e. movement rate – 18 h after the onset of each 24 h
experiment in tanks with a single tadpole age class. Two independent observers recorded
the number of discrete tadpole movements over 2 min, and counted the number of visible
tadpoles. Individual movement rate was calculated for visible tadpoles only, since the
number of dead tadpoles at this point was unknown. We compared tadpole movement rate
across age classes using generalized linear models with quasipoisson error distribution. In
the presence of belostomatids late hatchlings were about 5 times more active than early
hatchlings (χ2 = 26.52, df = 1, P < 0.0001, Fig. A2). However, the effect of hatching age on
activity was only marginally significant in the libellulid (χ2 = 3.83, df = 1, P = 0.050, Fig.
A2) and aeshnid (χ2 = 2.88, df = 1, P = 0.090, Fig. A2), experiments in which all tadpoles
were less active.
Figure A2. Activity of early-hatched and late-hatched tadpoles after 18 h of exposure to an
aeshnid dragonfly nymph (open circles), a belostomatid giant water bug (open squares), or
a libellulid dragonfly nymph (filled circles). Late-hatched tadpoles apparently reduced their
movement rate in the presence of dragonfly nymphs. However, this was not as effective as
a defense against aeshnids as the very low activity of early hatchlings due to their less
developed state.