No. From my fairly comprehensive database of 476 ecological meta-analyses, here’s a graph of weighted mean effect size vs. meta-analysis publication year:
This graph is very crude. It includes meta-analyses based on different effect size measures. And it’s not showing you error bars around those means (as you’d expect, the means that are farther from zero tend to have bigger error bars). But better graphs wouldn’t change the basic picture: there’s no trend over time. It’s not the case that ecologists decades ago discovered all the big effects, so that now we’ve all moved on to studying smaller effects.
This result doesn’t surprise me, and I’m guessing it doesn’t surprise most of you either. There’s an infinity of effects that ecologists could study. The supply of big effects is not some exhaustible finite resource. And ecologists’ choices about what effects to study don’t have much to do with how big those effects are on average.