# A comprehensive phase diagram for logistic populations in fluctuating environment

## TL;DR

This paper provides a detailed phase diagram for logistic population models under environmental fluctuations, identifying three distinct phases with different extinction time behaviors and analyzing the effects of demographic and environmental stochasticity.

## Contribution

It offers a comprehensive analysis of population phases considering both demographic noise and environmental variability, including phase transitions and breakdown of continuum approximation.

## Key findings

- Three distinct phases with different extinction time scalings
- Identification of phase transition points and breakdown of continuum approximation
- Insights applicable to ecological time series and conservation management

## Abstract

Population dynamics reflects an underlying birth-death process, where the rates associated with different events may depend on external environmental conditions and on the population density. A whole family of simple and popular deterministic models (like logistic growth) support a transcritical bifurcation point between an extinction phase and an active phase. Here we provide a comprehensive analysis of the phases of that system, taking into account both the endogenous demographic noise (random birth and death events) and the effect of environmental stochasticity that causes variations in birth and death rates. Three phases are identified: in the inactive phase the mean time to extinction $T$ is independent of the carrying capacity $N$, and scales logarithmically with the initial population size. In the power-law phase $T \sim N^q$ and the exponential phase $T \sim exp(\alpha N)$. All three phases and the transitions between them are studied in detail. The breakdown of the continuum approximation is identified inside the power-law phase, and the accompanied changes in decline modes are analyzed. The applicability of the emerging picture to the analysis of ecological timeseries and to the management of conservation efforts is briefly discussed.