🪻Section Two: more life histories

charts and charts and more charts!

🪻Photoperiod

Day length. A reliable cue organisms use to predict seasonal changes, because it changes the same way every year.

🪻Phytochrome

The plant pigment that senses day length by switching between two forms (Pr and Pfr) depending on red vs. far-red light.

🪻Grama grass flowering by latitude

At 47°N it flowers in late summer at 16 hours of daylight; at 30°N it flowers in autumn at 13 hours. Northern plants must flower while days are still long because winter comes earlier.

🪻Daphnia diapause by location

Alaska populations enter diapause at 20 hours of daylight; Michigan populations at 12 hours. Shows heritable, locally adapted cues.

🪻Diapause

A dormant resting state an organism enters to survive unfavorable conditions.

🪻Phenotypic plasticity

The ability of one genotype to produce different phenotypes depending on the environment it experiences.

🪻Frog metamorphosis with high food

Tadpoles grow fast and metamorphose early and large (point A).

🪻Frog metamorphosis with low food

Tadpoles compromise, metamorphosing somewhat later and somewhat smaller (point C), instead of same age but tiny (B) or same size but very late (D).

🪻Trade-off in frog metamorphosis timing

Metamorphosing early means earlier first reproduction; being bigger means better ability to escape predators.

🪻Snails with crayfish predators

Snails delayed first reproduction (about 77 vs. 59 days) and were about twice as big (213 vs. 110 mg), too big for crayfish to crush. Lifetime egg production did not change.

🪻Phenology

The timing of seasonal life history events, such as flowering, leaf-out and migration.

🪻Walden Pond flowering data

Plants now flower earlier than in Thoreau's time; warmer spring temperatures mean earlier flowering.

🪻Phenological mismatch

Species shift timing at different rates (leaf-out about 18 days earlier, insects about 13, birds only about 3), so birds may arrive after the food they need has peaked.

🪻Why birds shift less than plants

Birds time migration partly by day length, which hasn't changed, while plants and insects respond to temperature, which has.