1) Organic matter is recycled in an ecosystem by decomposers. Decomposers are organisms such as bacteria and fungi that break down the organic matter in the dead bodies of plants and animals. As the decomposers feed from the dead animals, they break down the organic compounds into simple nutrients.
2) By removing the jaguar from the food web, we are removing one of the predators. This can cause a surplus in both the population of the mammals ( rabbit and the other one) because there is not something that is actively eating and keeping the numbers at bay. Essentially, if you remove the jaguar you will mess up the loop, causing an increase of population that could possibly cause harm. Also, by taking the jaguar out of the food web, the decomposers would not be able to decompose fecal, animal carcasses, etc. because the jaguar is not actively killing something and furthering along this process. Hope this helps!