In my world, there is a region of land that is highly windy, but at high altitudes. This makes it highly likely that many plants and animals of the region will use this to it's potential. I have thought of many different designs for plants and animals such as a cat with wings that are designed to prey on the regions birds. However, I feel a lot is missing from this ecosystem. So my question is: what would the animals an plants be like in this ecosystem and how would they function in symbiosis in a marshy island located in the center of a river? Note that the ground is also cold and windy, and it has a river flowing right through the center. Also, there are many big mountains as well as towering forests.
First, its not good for trees to be tall in windy places, the taller they are the more force they have to resist till eventually they cant any longer. (big reason why you don't see many tall trees on a windy plain)
Anyways, many plants use the wind to carry seeds or pollen so they can reproduce more effectively. These seeds and pollen can be a food source and it can be a dense one. You could have insects that eat this. You could have different sizes of flying filter feeders who eat the insects or pollen/seeds kind of like a flying whale.
Then you could have creatures that eat the filter feeders and so on and so forth.
As with any ecosystem, you start with organisms that take in energy and do something. Then you make organisms that eat them and bigger organisms that the little ones till eventually you have Lions.
You may want to rethink the wind factor of your environment if you've decided on the flying animals. High wind conditions are very difficult for winged creatures. The usual populations of high wind areas are going to be wingless insects, ground-dwelling animals, and only those powerful birds which can build the most secure nests.
Depending on how dry the area is, soil erosion could be a big problem. Too dry, and this may turn into a barren wasteland. However, some of the more windy places on Earth can have flourishing ecosystems of the kind you seem to be looking for, but the wind is less powerful. Overall, however, the availability of water will be the greatest determining factor of the type of ecosystem.
Another thing to consider is that even the windiest places will not have wind blowing constantly. At most, it'll be around 70% of the time.
This source has a ton more information about high wind effects on ecosystems:
Wind caused airflow across the surface of leaves leads to increased transpiration and gas exchange between leaf and atmosphere. The displacements of branches and leaders leads to responses such as more flexible wood, increased thickening of stems and roots (probably structural), and reduced shoot extension. Short story, windy environments produce roots with improve root anchorage, and shorter, thicker and less slender trunks and branches in order to better resist to deflection.
Also, there is a lot of tree breaking and steam snaping in those environments, a lot of trees death... But on the other hand, they are often able of resprouting. Dead standing and downed trees are very commom in windy forest ecosystems, and they are the basis of a huge ecosytem on their own... e.g. habitat and substrate for microbial, insect, plant and animal communities... This environment provided by dead trees is very dinamic once they are under decomposition process
You can explore wind pollinated tree species... Their flores often have hairy and or sticjy flower stigmas, in order to trap pollen. And also, wind disperser fruits and seeds are ofen small, very light, dry and very aerodynamic.
For animals as well, think about aerodinamic, anti wind adaptations, and wind based traps... (e.g. spider webs in positions to catch insects flying around)
You might want to read this very good reference to learn more about windy ecosystems:
S.J. Mitchell; Wind as a natural disturbance agent in forests: a synthesis, Forestry: An International Journal of Forest Research, Volume 86, Issue 2, 1 April 2013, Pages 147–157, https://doi.org/10.1093/forestry/cps058