Invasive mammals are responsible for the majority of native species' extinctions on islands. While most of these extinction events will be due to novel interactions between species (e.g. exotic predators and naive prey), it is more unusual to find incidences where a newly invasive species cause the decline/extinction of a native species on an island when they normally coexist elsewhere in their overlapping mainland ranges.

We investigated if resource competition between two insectivorous small mammals was playing a significant role in the rapid replacement of the native pygmy shrew (Sorex minutus) in the presence of the recently invading greater white-toothed shrew (Crocidura russula) on the island of Ireland.

We used DNA metabarcoding of gut contents from >300 individuals of both species to determine each species’ diet and measured the body size (weight and length) during different stages of the invasion in Ireland (before, during, and after the species come into contact with one another) and on a French island where both species have long coexisted (acting as a natural ‘control’ site). Dietary composition, niche width, and overlap, and body size were compared in these different stages.

The body size of the invasive C. russula and the composition of its diet change between when it first invades an area and after it becomes established. During the initial stages of the invasion, individual shrews are larger and consume larger-sized invertebrate prey species. During the later stages of the invasion, C. russula switch to consuming smaller prey taxa that are more essential for the native species. As a result, the level of interspecific dietary overlap increases from between 11–14% when they first come into contact with each other to between 39–46% after the invasion.

Here we show that an invasive species can quickly alter its dietary niche in a new environment, ultimately causing the replacement of a native species. In addition, the invasive shrew could also be potentially exhausting the local resources of larger invertebrate species. These subsequent changes in terrestrial invertebrate communities could have severe impacts further downstream on ecosystem functioning and services.

This is a metabarcoding dataset for Browett, S.S., Synnott, R., O'Meara, D., Antwis, R.E., Browett, S.S., Bown, K., Wangensteen, O., Dawson, D.A., Searle, J.B., Yearsley, J.M. and McDevitt, A., 2022. Resource competition drives an invasion-replacement event among shrew species on an island. bioRxiv. doi: https://doi.org/10.1101/2022.04.27.489660

Briefly, DNA was extracted from the gut contents of >300 shrews (Sorex minutus and Crocidura russula). The COI region was amplified using a primer set referred to as Gillet. There are eight multiplexed fastq files from each of the two sequencing runs. Four forward read files and four reverse read files for each run. Samples were multiplexed using primers with dual-index 8 base pair MID tags on them. The sequences contain the primer region and MID tags. A file with the list of tags and primer sequence is included. Sequencing adapters were ligated using a PCR-free method. The final library with a total of 303 samples, five extraction blanks, and 20 PCR blanks was sequenced on two Illumina MiSeq runs using V2 2x150 bp cycle kits, both loaded at 9pM with a 5% PhiX (v3, Illumina) spike

For full details on data collection, preparation and sequencing, see https://doi.org/10.1101/2022.04.27.489660 (and forwarding link to published article) and https://github.com/ShrewlockHolmes/

Further information on samples is also available from https://github.com/ShrewlockHolmes/

The list containing the MID tags and individual sample names for each library are included. The columns are

1: Primer used

2: Sample ID

3: Forward MID tag

4: Reverse MID tag

5: Forward primer sequence

6: Reverse primer sequence

7:9 misc info required for pipeline used for the article.