How to seek for available genetic data relevant to ecology and evolution?
As a bioinformatician, one of my tasks is quite often to get information from databases or find the correct database to compare to. There are several big databases around, but even those are way too many for any single person to know.
There are databases specialising on genetic data, some specialising on taxonomic information, some on ecological information and then there are species specific databases which collect all kinds of data from a given species, genus or clade.

For me the biggest source of generalised information would be the NCBI databases, including GenBank for nucleotide sequence, their Protein database and maybe dbSNP for, well, SNPs. Then there are multiple 16S databases I have used, there is UCSC for the basic data about the human genome, flyBase for Drosophila,... I think the point should be clear. And those are only the ones that just sprang to my mind.

If you don't have a very exact question to answer like "Is there a gene similar to gene x from Drosophila present in any Bacteria?" it can be very hard to both choose the correct database and also find the important information in it efficiently. 

Then there is the problem of metadata. I might be able to find sequencing data from the gut microbiome of a human treated with antibiotics quite easily. If I am looking for a specific antibiotic given over a minimal time of seven days to a different healthy humans, preferably including at least one breastfed child and it's mother (which was the one taking the antibiotics, not the child), then it's getting complicated. Here it is generally way easier to scan PubMed for some relevant publications on the matter and find out if they used published datasets or published their own.