Grassland Invertebrates
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Increase presence and abundance
Data collection in progress
Kakheti Steppes
Georgia
Problem: Combined pressures in this landscape such as overgrazing, increasing temperatures and less rainfall, leading to erosion and desertification, are contributing to less diverse and less abundant insect communities.
Action: SABUKO is working with farmers and shepherds to increase their participation in rotational grazing, which means that portions of the pastures will be left ungrazed at any given time to recover from the grazing season. This will promote increases in the diversity, cover and biomass of grassland plants, which will in turn benefit the invertebrate populations.
Indicator: Grassland invertebrates are excellent indicators of grassland quality due to the various functions they perform in that ecosystem, such as nutrient cycling, pollination, and herbivory. The rate at which arthropod diversity recovers following the change in management practices indicates the rate at which a healthy grassland and its ecosystem function recovers.
Methods
SABUKO is monitoring the insect orders in four land management types shown on the map below (Fig. 1), including conventionally grazed grasslands (control area) and different types of rotationally grazed grasslands (treatment areas):
- Control: overgrazing, business as usual.
- Rotational grazing implemented since 2019.
- Rotational grazing – restrictions applied since 2019.
- Rotational grazing to be implemented in future.
Figure 1: Map of sampling sites across different land management interventions.
For each management type, two plots were established, each containing three sampling subplots. Each subplot was 50 x 50 m and distance between sub-plots was 200 m (see Fig. 2).
Figure 2: An example of the sampling design, depicting the two plots in the Rotational Grazing – to be implemented in the future management type. Each red circle depicts the plot, and the yellow squares depict the sub-plots.
In each sub-plot, sampling was performed for one hour with one expert making observations for each of the following insect orders:
- Diptera
- Hymenoptera
- Hemiptera
- Coleoptera
- Orthoptera
- Lepidoptera
- Araneae
The first sampling took place in July 2023. Specimens were collected by hand and by sweep netting and stored in 96% ethanol, or in the case of Lepidoptera, preserved dry. Identifications were then made in the lab to species level, and the sum of individuals in each order, across the three subplots per plot were computed as a final variable. Additionally, an indicator species analysis was conducted in R (Dufrene and Legendre, 1997; De Caceres et al., 2010, 2012; De Caceres and Legendre, 2020) to see which species are most strongly associated with which management types. Monitoring will be repeated in July 2027 to assess any change over the project timeframe, since rotational grazing has been underway.
Results
Despite data collection occurring in July, when unfortunately there were almost no flowering plants available and therefore a general absence of the major pollinator groups, SABUKO collected 13,567 specimens in total. Total abundance of insects (see Fig. 3 below, left panel) differed significantly between sites under different management types (χ2(3) = 1399.8, p < 0.001). Despite equal sampling effort, the control site and the rotational grazing to be implemented site had higher overall abundances than the two sites where rotational grazing is already implemented. These baseline results suggest that more intense grazing has some beneficial impact on insect abundance. In contrast, species richness (see Fig. 3 below, right panel) did not differ significantly between sites with different management strategies (F(3,20) = 2.7; p < 0.08). When this data is reassessed in the coming years, it will be interesting to see if species richness remains unchanged across all management types, or increases where rotational grazing has continued to be implemented.
Figure 3: Total abundance and Shannon-Wiener diversity index of invertebrates in sites under different management types. The Shannon-Wiener index quantifies species richness, and here is calculated for taxonomic orders rather than species.
Follow up
The project will repeat this monitoring in 2027 to learn how insect abundance and diversity has changed in each site over time.
References
De Caceres, M., Legendre, P., Moretti, M., 2010. Improving indicator species analysis by combining groups of sites. Oikos 119, 1674–1684.
De Caceres, M., Legendre, P., Wiser, S.K., Brotons, L., 2012. Using species combinations in indicator value analyses. Methods Ecol. Evol. 3, 973–982.
De Caceres, M., Legendre, P., 2020. How to Use the Indicspecies Package (ver. 1.7.8). R Project, 30.
Dufrene, M., Legendre, P., 1997. Species assemblages and Indicator species: the need for a flexible asymmetrical approach. Ecol. Monogr. 67, 345–366.
