Global Change Ecology: Ranges, Phenology and Regime Shifts

You have separated suitable conditions from the ability to reach them. Warming often moves cool conditions poleward or uphill, but responses vary by region and species. A species may expand, contract or shift its range. Conditions for survival and reproduction, not temperature alone, determine which places are suitable.

Phenology is the timing of seasonal events. A phenological mismatch reduces useful overlap between partners whose timing shifts differently. Khan Academy describes Greenland sanderling chicks hatching after peak invertebrate food, with lower survival. Subtract the food-peak day from the hatching day. In a hypothetical season, food peaks on day 12 and chicks hatch on day 17: 17 - 12 = 5 days.

Heat stress can cause corals to lose symbiotic algae and bleach. Bleached corals are stressed, not necessarily dead. They can recover if conditions improve, while prolonged stress can cause mortality. Bleaching alone does not prove that a reef has entered a persistent alternative ecosystem state.

A threshold response can turn a gradual pressure into an abrupt change. Below a threshold, a system may absorb increasing stress. Beyond it, rapid change can occur. The speed of the pressure therefore does not determine the speed of the response. An abrupt change is not automatically irreversible.

A regime shift is a substantial, persistent change in ecosystem structure or function. In an urchin barren, urchins can survive on other food and graze new kelp. That feedback can hinder kelp recovery after heat eases. Recovery may require reduced grazing as well as cooler conditions. Different thresholds for collapse and recovery are called hysteresis.