The producers of this food web are plants; they can produce their own food. The first-order consumers are nematodes, fungi and bacteria. The high-order consumers are birds, animals and arthropods. The decomposers are bacteria and fungi. After an organism dies, they rot and gets, well, decomposed by the decomposers (i.e. fungi & bacteria). The 2 spieces which compete each other for food are birds and animals (maybe). The 2 spieces which doesn't have a preadator are birds and animals.
That was Part A, so I wasn't finished yet. This is Part B:
If the foxes disappeared, then the rabbits will over-populate and the grass might be extinct. If the predaceous insects disappeared, then the toads will all die out or have to eat something else. If the spiders disappeared, then the predaceous insects' population will stay the same because the spider isn't the only preadator of the predaceous insect. If the foxes & snakes disappeared, then nothing will happen to the hawks & owls because nothing's connected to them & the foxes (maybe). The population of the foxes will decrease if the population of the hawks & owls increases because the hawks & owls eat the same types of food as the foxes. The 2 speices which compete with each other for food are foxes & hawks. 2 of the first-order consumers are rabbits and seed eating birds. 2 of the preadators are spiders and toads.