Wild Animal Suffering is the biggest problem, by far in the entire world. Now, first I want to say that it is not just one problem; if we consider malaria (one problem) cases in humans (one species), in children (one age group), in Sub-Saharan Africa (one area) to be one problem, then think about this; there are 8 million SPECIES of animal on earth, many with vastly more members than humans, with much higher mortality rates, and there are far more diseases and problems than Malaria that contribute to their suffering, which is in far more than Sub-Saharan Africa. This means that if we can get that specific with animals with their problems too, then there are probably hundreds of trillions or more of Wild Animal Suffering problems, which we simply group into one group. If we group all of those hundreds of trillions of problems into one, it is by far, easily, without a doubt the biggest problem in the world; we estimate there are 20,000,000,000,000,000,000, or 20 quintillion wild animals on earth; about 2500000000x the number of humans!
So if this is easily the biggest "problem" on earth, dwarfing all others, surely we prioritize it when we give, right? Nope. The problem that is 2500000000x bigger than all human problems combined gets astronomically less funding (I am not even going to look up the statistic, because almost anyone who researches effective altruist charities, or charities in general, knows that we give huge amounts to relatively small human problems (which I know is controversial to say because the scale of human suffering is completely unimaginable; but it is still hugely outnumbered by this), also huge amounts to charities that deal with problems caused by humans to other animals (like factory farming), but very little to charities that deal with wild animal suffering!
Now, why is this? After all, we already know that wild animal suffering most likely severely outweighs wild animal happiness. A popular strategy in the wild used by many animals is the r-strategy, where they produce thousands of offspring, provide little care, and the vast majority die slow, painful deaths by the time they reach adulthood. However, the main excuse for us not helping is that we have literally no idea what we are doing!
First, we do not know which animals have the capacity to suffer and which don't; especially with the small ones. Copepods (small, very simple ocean-dwelling invertebrates) make up the majority of all animal life on earth, but we do not know if they can feel basic pleasure or pain! We aren't even sure about the much, much more complicated and intelligent ants! We don't know how sentient they are relative to humans, or anything! However, there is a solution to this: pour research money into the research on the sentience of the smallest, most populous animals; the ones that pose the biggest problems. We do not need more research on pigs, cows, rats, or even chickens. We need it more on insects; ants, bees, and other small, extremely populous animals. But we need it most on the animals where there are such huge amounts that they outnumber everything else, and are simpler than arthropods (like copepods!), but they might, just might have the ability to experience basic pain and pleasure, in which case their suffering is the most important problem on planet earth. We need welfare ranges for the smallest, least sentient animals first.
Second, we don't know what will happen when we change the ecosystem; we could very easily do something to change the ecosystem to prevent suffering and cause it on an unimaginable scale instead! However, the solution to this is simple; research! A few hundred years ago, we prescribed deadly leeches for medical problems, and knew very little about the human body. However, through research, we figured out how to eliminate diseases, remove tumors, and so much more. We could do the same thing we did for the human body for ecosystems if we just put research into finding interventions to prevent suffering.
I think if we pour research money into those two causes, we will soon be able to figure out how to prevent suffering on an unimaginable scale, and produce the best, cheapest, most utilitarian interventions/charities to prevent suffering ever created.
