I will admit that far from every zoo does uses it's megafauna even close to their maximal potential nor mixes it enough with smaller animals. Maybe my local area is also not really a great sample of this with many zoos highly involved in in-situ conservation, something I didn't really consider up to this point. Though Olmen/Pakawi is a great example I believe of a Belgian zoo not using this potential at all. They don't contribute to in-situ conservation and they barely contribute to proper ex-situ conservation. They do have a lot of small species, but little of conservational importance. This does seem to go hand in hand with their highly outdated enclosures showcasing too many species for the size of their park, so maybe the next owner will finally make real change (or with much luck the current new owner, though I have my doubts as it's the son of the previous one).
That is an interesting observation, I don't know much about Olmen zoo but I would say that if it doesn't perform well in terms of ex-situ and in-situ conservation then it is hardly alone in that and in fact most zoos underperform in this regard.
That total income is what I think matters very much. Zoo Antwerpen and Planckendael could certainly keep less megafauna and more smaller animals, at the cost of it's visitor numbers and total net income however. By mostly being two parks with multiple species megafauna they are able to generate far more net income however. Whilst this might decrease their importance in ex-situ conservation of smaller species this does allow them to invest more in in-situ conservation. This in-situ role is something I value much more then their ex-situ role in most species (wether it is small or large). If thus for the purpose of generating in-situ funds I believe keeping a large amounts of megafauna is justified, even when it comes at the expense of ex-situ keeping of smaller species. The KMDA does seems to balance a bit between the two, with both decent in-situ work but to a certain extent also ex-situ programs with birds, amphibians and reptiles. I do think that zoos each have the option to choose their own balance between an important role of ex-situ conservation (thus more small species, often behind the scenes to reduce costs) or towards in-situ. Only in Planckendael I think adding some small species could make it more attractive, but rather as an addition to their megafauna and not at the cost of it.
But do you really a reduction of megafauna would translate into a loss of visitor numbers ?
I do agree with you about the importance of in-situ conservation often being greater than ex-situ efforts.
That said, I would say that it is very important to investigate further and think critically about what actions zoos state they are doing in-situ and to ask whether this is actually accurate because often it is insufficient.
I suppose I would somewhat disagree with you there on the issue of ex-situ keeping of smaller species by zoos and that keeping megafauna often translates into greater returns in terms of in-situ conservation. It is very much a case by case situation and each zoo and its merit in this regard must be judged separately.
However, this benefit doesn't scale up, as at a certain point small species become repetitive for your average visitor. Especially non-mamalian species suffer this fate, as for many people every frog is just a frog, every beetle just a beetle and every snake just a snake. So at a certain point visitors drop interest, and adding more of those exhibits doesn't lead to an increase in visitor numbers anymore. The way of displaying these creatures does matter a lot, and spreading them out alongside megafauna is one of the ways that people keep being interested in those smaller species cause it's unknown species after unknown species but a mixup. The same applies for megafauna too by the way, simply having megafauna alone without less popular filler species is also not the most optimal. Small side-exhibits give visitors more to explore, something both us hardcore zoofans and regular visitors do seem to appreciate. Especially when well-integrated into these megafauna-exhibits, alternating viewing points of the same megafauna with several smaller side-species makes people both stay interested in small species and spend more time with those megafauna. But this way those small species are thus reliant on megafauna. In certain places like a small reptile zoo or an aquarium (though there sharks and large fish fulfill similar roles as megafauna) this can work, but in non-aquaria this greatly limits their size and thus their total net income generated.
Again, yes, income is very important but the question is how much of it reaches in-situ conservation efforts ?
It was once estimated that about 3 % of the budget of over 200 accredited zoos in the USA actually goes directly to in-situ conservation. At most zoos it is even less and is at 1% of their annual budget to in-situ which just doesn't cut it IMO. If it was 10 % then a lot more could be done in terms of in-situ and there would be far more to feel proud about but at the moment, if we are honest it just isn't enough.
When the Los Angeles zoo built their elephant enclosure they spent $42 million dollars on constructing this and can you imagine what could be done with money of that kind in terms of in-situ efforts for elephants or indeed ex-situ for smaller taxa ?
Moreover, if the argument hinges on the economic benefits, does the keeping of elephants do anything for the conservation of the species either in ex-situ terms or in-situ if so little zoo money actually reaches these species in the wild ?
My answer to that would be no and if they are not there for any reason other than because the public like elephants and if the money generated is insufficient for in-situ then why not focus on the ex-situ of a smaller species that does in fact need to be there and is compatible with being held under captivity ?