How climate gradient and land use affect insects

Urbanization and agriculture without green planning lead to decrease in insect biomss and richness

Insects are important players in ecosystems, and for human related activities. From pollination to pest suppression, their contributions have high economic value and their declines are therefore gaining evermore global attention. Even though the decline in insect biodiversity and its indication that ecosystems are suffering are generally accepted facts, there is little evidence for this process in the form of data due to the efforts needed for designing projects and collecting data to show the insect decline. The ideal projects are long term, cover a wide range of locations which makes them costly and time consuming. But long-term monitoring is necessary in order to help improve policies and to validate if implemented policies are having the desired effects. Space-for-time studies help to fill in gaps for lack of long-term data in the short term. This is because such studies include large number of sampling locations which allows the assessment of climate and land-use impact on all land-use types: semi-natural, agricultural, and urban.

In light of this, research groups in Germany — i ncluding University of Würzburg, Technical University of Munich, AIM GmbH and others — have joined forces in a large project covering different parts of the country across time in order to check what variables are most important for insects to thrive.

This was done by collecting insects using Malaise-traps in 179 sites along a climate gradient and then using AIM’s DNA metabarcoding methodology to identify the species present in the samples.

Figure from Uhler et al (2021): Relationship of insect biomass and richness with land use along a climate gradient. Nature Communications, Open Access, 12 October 2021, doi.org/10.1038/s41467–021–26181–3

The research groups performed many comparisons and analysis. The main take-away results are:

1. Insect richness and biomass increases with increasing temperature;
2. Semi-natural and urban environments that differ the most in biomass: ongoing urbanization leads to decline in biomass;
3. Semi-natural and agricultural environments differ the most in species richness: conversion to agriculture leads to decline in species richness.

From these results we can suggest that insects need more green spaces in urban environments so their populations can be supported. In agricultural areas, the existing agro-environmental schemes should be further expanded to increase habitable areas for insects which will lead to increased diversity.

Vocabulary:

Biomass: the mass or weight of living tissue, the mass of living biological organisms in a given area or ecosystem at a given time.

Species richness: the number of species within a defined region, simply a count of species, and it does not consider the abundances of the species or their relative abundance distributions.

Space-for-time (SFT) study: spatially separated sites selected based on either ecological or environmental gradients serve as proxies for predicting ecological time-series.

Publication

Uhler et al (2021): Relationship of insect biomass and richness with land use along a climate gradient. Nature Communications, Open Access, 12 October 2021, doi.org/10.1038/s41467–021–26181–3