# Tipping Phenomena and Points of No Return in Ecosystems: Beyond Classical Bifurcations

## TL;DR

This paper analyzes critical transitions in ecosystems under environmental change, introducing criteria for nonautonomous tipping points, and explores how different bifurcations and basin instabilities influence ecosystem resilience and tipping behavior.

## Contribution

It provides new criteria for identifying nonautonomous tipping points and introduces basin instability as a key concept in understanding ecosystem responses to environmental changes.

## Key findings

- Identification of nonautonomous tipping criteria using autonomous system properties
- Discovery of tipping tongues and wiggling bifurcation curves in parameter space
- Insights into points of no return and return tipping in ecosystem dynamics

## Abstract

We discuss tipping phenomena (critical transitions) in nonautonomous systems using an example of a bistable ecosystem model with environmental changes represented by time-varying parameters [Scheffer et al., Ecosystems, 11 (2008), pp. 275--279]. We give simple testable criteria for the occurrence of nonautonomous tipping from the herbivore-dominating equilibrium to the plant-only equilibrium using global properties of the autonomous frozen system with fixed-in-time parameters. To begin with, we use classical autonomous bifurcation analysis to identify a codimension-three degenerate Bogdanov-Takens bifurcation: the source of a dangerous subcritical Hopf bifurcation and the organizing center for bifurcation-induced tipping (B-tipping). Then, we introduce the concept of basin instability for equilibria to identify parameter paths along which genuine nonautonomous rate-induced tipping (R-tipping) occurs without crossing any classical autonomous bifurcations. We explain nonautonomous R-tipping in terms of maximal canard trajectories and produce nonautonomous tipping diagrams in the plane of the magnitude and rate of a parameter shift to uncover intriguing R-tipping tongues and wiggling tipping-tracking bifurcation curves. Discussion of nontrivial dynamics arising from the interaction between B-tipping and R-tipping identifies "points of no return" where tipping cannot be prevented by the parameter trend reversal and "points of return tipping" where tipping is inadvertently induced by the parameter trend reversal. Our results give new insight into the sensitivity of ecosystems to the magnitudes and rates of environmental change. Finally, a comparison between "tilted" saddle-node and subcritical Hopf normal forms reveals some universal tipping properties due to basin instability, a generic dangerous bifurcation, or the combination of both.