# The Relationships between the Population Density of Fir Bark Beetles and Niche Breadth

## TL;DR

This study explores how the population density of fir bark beetles affects their niche breadth, offering a method to monitor climate change impacts on beetle populations.

## Contribution

A new method for monitoring climate change impacts on bark beetle niche breadth with high precision and low estimation errors.

## Key findings

- The niche breadth of bark beetles is correlated with population density.
- Derived models explain 77–84% of the variation in niche breadth with estimation errors under 20%.
- The method can be used to model climate change effects on beetle population dynamics.

## Abstract

Determining the ecological niche breadth of various organisms is a key objective in contemporary biological research. Studies of this type play a significant role in describing biotic interactions, which is becoming particularly important in the context of observed climate change. A method has been developed that enables the monitoring of the impact of climatic changes at the local level, in specific tree stands. The statistical foundations of the method enable the computation of errors of estimation. The method offers a high precision and explains approximately 80% of the variation in the niche breadth of bark beetles on natural traps, while the mean relative errors of estimation do not exceed 20%. The niche breadth parameter obtained from the derived regression equations may be used in models that describe—for example—the impact of observed climate change on the population dynamics of bark beetles. The results suggest a need for further research to derive regression equations for firs growing in different regions of Europe.

Bark beetles are a significant link in the chain of diseases that lead to the accelerated dying of firs (Abies alba Mill.), a key species in the cultivation of stable mixed-tree stands. The aim of this work was to evaluate biotic interactions in populations of bark beetles that colonised natural traps made from firs. The tested hypothesis was that the niche breadth of the species increases with the increasing density of the population. The research was carried out in near-natural forests containing fir, growing in the Suchedniów-Oblęgorek Landscape Park in central Poland. Data were collected from 30 traps trees and 30 windfalls in the years 2010–2023. Cryphalus piceae Ratz. prefers heavily weakened trees, as shown by the fact that it colonised all of the natural traps, which lack any defensive reactions. The sampling method used in the study proved effective, as confirmed by the segregation of the niches of all of the bark beetles. Using nonlinear regression (linearisable model and piecewise linear regression), models were constructed that describe the niche breadths of the bark beetles. The niche parameter is correlated with the density of colonisation. The derived models explain around 77–84% of the variation in the niche breadth of bark beetles on natural traps. The mean relative errors of estimation do not exceed 20%. The niche breadth parameter obtained from the derived regression equations may be used in models that describe—for example—the impact of observed climate change on the population dynamics of bark beetles.