DNA extraction, PCR and sequencing
For this study, we focused on nectar and fruit eating species, which produced faecal samples consisting of either seeds or digested fruit pulp. For the DNA extraction, PCR and sequencing of the samples we followed standard protocols for plants and all works was conducted by the Canadian Centre for DNA barcoding (CCDB) following these procedures (Ivanova, Kuzmina, & Fazekas, 2011). In brief, dried plant material from faeces (fruit pulp or seed) was placed in a sterile strip-tube with pre-aliquoted sterile stainless steel beads and the tissue was ground using a Tissue Lyser (Qiagen, USA). The ground material was incubated with 2x CTAB buffer at 65°C for 1 hour and DNA extraction was performed using a semi-automated glass fiber filtration method (Ivanova, Fazekas, & Hebert, 2008; Fazekas et al. 2012). Following established methods, we amplified a 552 bp fragment of the 5’ end of the large subunit of RuBisCO (rbc L) and the ~350 bp second nuclear encoded internal transcribed spacer (ITS2) flanking by the partial 5.6S and 26S ribosomal genes. Sanger sequencing was performed using a ABI 3730xl capillary sequencer (Ivanova, DeWaard, Hajibabaei, & Hebert, 2005; Ivanova & Grainger, 2006; Kuzmina & Ivanova, 2011a; Kuzmina & Ivanova, 2011b; Fazekas et al. 2012). Although plant DNA barcoding yields lower species resolution compared to fungi and animals (Hollingsworth, Graham, & Little, 2011), generally it provides robust results for identification of vascular plants at the genus level (Kress et al. 2009; Parmentier et al. 2013; Braukmann, Kuzmina, Sills, Zakharov, & Hebert, 2017). For the samples from the normal year, plant specimens collected on the sites were identified using rbcL andmatK and the supplementary non-coding plastid regiontrnH-psbA (see Clare et al. 2019 for full methods).