In broad strokes adult organisms play a more significant role in supporting the flourishing of many beings than the unborn/seeds. I don't really look at it in terms of "more valuable" - all beings have their role within the Weave. The long thread that weaves through and touches many things has a greater impact when severed on the integrity of the whole than the short thread that touches but a few. The acorn might survive to become the oak and the acorn serves to sustain many other beings as foodstuffs, but most acorns will die and perish and without the oak there are no more acorns. Both the acorn and the oak are important, but preserving the oak is necessary to sustain that part of the Weave.
No. For me there is no "deciding factor" (singular). I'm not that simplistic in my assessments. Thinking in terms of the whole web of being necessitates deeper consideration of the whole. No one thing is determinative, certainly not species (I'm not speciesist). That's why I say the scenario doesn't present enough information or context. There are many things to weigh when considering the flourishing of the Weave. That's thinking like an ecologist - you don't keep the lake clean and forget to mind the river that feeds it. It's all interconnected.
Fair enough. No, I don't find killing of animals (or anything) to be wrong in of itself. Death, destruction, and decay are inherent and necessary properties of the reality we live in. There is no creation without destruction - matter is not created or destroyed it only changes form. Death is required for life, always. To declare unequivocally that "killing is wrong" is to declare unequivocally that "the universe and all reality is wrong." Perhaps some lifeways and religious traditions are comfortable with such proclamations. I am not - the dance and cycles of death-life-death-life are a reality I accept and celebrate.
It's less an equation than the fact that I view all things as bearing equal intrinsic value. This isn't uncommon for environmental ethicists. The value of a thing is on its own merit, intrinsic, and independent of whatever some human wants to say about it. As such, I don't rank order things. I don't say "oh, those kittens are more valuable than that stand of oak saplings." That's nonsense to me. They are both sacred, holy, and divine. Life is holy, death is holy, wellness is holy, sickness is holy, it all serves its role within the Weave.
That doesn't mean I have the same relationship to different things, though. All humans will prioritize that which they have deeper relationships with. I am far from an exception to that. Because I work deeply with the Green and the Land itself, I consider it more deeply than most other humans are going to. I'm not gonna go into the mystical stuff in this thread, but I have had a lot of profound experiences communing with plants and the land. It's a Druid thing. It suffices to say that when you actually take the time to relate to everything in the world around you as a being it... you understand through experience how "person" applies to more than "human" or "animal."