Preface
This post will address death & pain separately. Both death without pain and pain without death are possible.
This post will use scriptures of The Church of Jesus Christ of Latter-day Saints, but it does not represent official teachings of the church.
Animals have an afterlife
In Revelation chapter 4, John sees a vision of heaven which includes animals. The following are questions Joseph Smith asked, and answers he received from the Lord, which pertain to animals in the afterlife:
2 Q. What are we to understand by the four beasts, spoken of in the
same verse? [Revelation 4:6]
A. They are figurative expressions, used by the Revelator,
John, in describing heaven, the paradise of God, the happiness of man,
and of beasts, and of creeping things, and of the fowls of the air;
that which is spiritual being in the likeness of that which is
temporal; and that which is temporal in the likeness of that which is
spiritual; the spirit of man in the likeness of his person, as also
the spirit of the beast, and every other creature which God has
created.
3 Q. Are the four beasts limited to individual beasts, or do they
represent classes or orders?
A. They are limited to four individual
beasts, which were shown to John, to represent the glory of the
classes of beings in their destined order or sphere of creation, in
the enjoyment of their eternal felicity. (Doctrine & Covenants 77:2-3)
Other animals are not created in the image of God, they are not the children of God, and they are not potential heirs of God, like humans are (for these characteristics of humans, see Romans 8:16-17, Genesis 1:26-27). They are not moral agents in the way that humans are (2 Nephi 2:14,16,26). But they are creations of God (see Genesis 1:20-25). God's creations are not abandoned to this temporary, fallen world (see passage quoted above, also Isaiah 11:6-9, Ezekiel 36:35, Hosea 2:18, 2 Peter 3:13). Jesus Christ overcame this fallen world and through the resurrection rescues all His creations from physical death (rescue from spiritual death is another matter that will not be covered here).
Animals will not inherit everything humans have the capacity to inherit, but they are destined for an afterlife characterized by felicity. The fact that their destiny in God's plan is different from that of humans does not mean that for them there is no purpose and there is no plan.
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Death
To borrow an idea from Albus Dumbledore=), to the well organized mind, death is but the next great adventure.
To assume there is no afterlife, and on the basis of that assumption reject the existence of God, is to argue in a circle. This circularity exists whether the subject is the death of humans or the death of animals.
If animals have an afterlife (discussed above), then the arguments that human death is not irredeemably unjust or irreconcilable with a loving God are also applicable to animals. For animals, this mortal life is just a brief stop along a journey. Progressing to the next portion of that journey is not in and of itself inherently bad.
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Addressing a counter-argument
To be sure, if death without suffering were philosophically problematic on its own, the concerns identified in the OP with respect to animals would be equally relevant to plants. I've yet to encounter anyone arguing that a loving God cannot be reconciled with so much death among broccoli.
The hedonistic counter-argument, that the purpose of life is pleasure, which animals can experience (to varying degrees), but plants cannot, is morally bankrupt. It's an awful slippery slope. The extreme to which I have seen this argument taken (I will not share links because I do not wish to give clicks to those espousing this view) includes those who believe that the purpose of life is sexual pleasure. I emphatically reject this shallow, short-sighted, life-deprecating view. It leads to prioritizing one's own temporary pleasure over the well-being of others. Such a view is rejected ethically here and theologically here.
The purpose of life is far more enduring than fleeting fun (see 2 Nephi 2:25-27, Romans 8:16-17, Moroni 7:48). If there is nothing in this world that cannot be improved upon in eternity, death is not at all inconsistent with a loving God.
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An important clarification
This does not mean killing people or animals just to send them on to eternity is good or sanctioned by God. This life is a sacred gift from God. What He gives He can take away (see Job 1:21). Animals were created for the use of man, not the abuse of man (Genesis 1:29, Doctrine & Covenants 104:17-18). Killing innocent humans is condemned by God (see Exodus 20:13).
One of the most significant pieces of progress in human philosophy was recognizing legally what God had already revealed centuries before: life is a God-given, natural human right (Recommended reading includes Richard Hooker, John Locke, and Thomas Jefferson, whose world-changing ideals--which they wrote and aspired to but didn't always live up to--were inspired by none other than...the Bible). Taking away human life isn't simply wrong if it inflicts pain, it is man assuming for himself that which is the prerogative of God. God gave man dominion over the animals, not dominion over other men. Murder deprives God's children of valuable learning experiences during the time of probation and preparation that mortal life occupies in the plan of salvation.
If the trials of mortal life were unnecessary, why didn't God just skip over that part and send us all directly to the next step? The development in this life and the receipt of a physical body are fundamental parts of the plan. They are not distractions from eternity, but preparation for eternity.
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Pain
Purpose of pain
It's tempting to think of pain as inherently bad. But what purpose does pain serve? It can certainly be a memorable instructor. It is also a protection. Pain guides an organism to avoid harmful behavior which can damage or destroy its physical body (e.g. the sharp recoil we exhibit upon feeling the pain of touching boiling water generally prevents prolonged exposure to boiling water, which would cause permanent scarring or death).
If mortal life in a physical body is an important part of God's plan -- even for animals -- then equipping animals with a defense mechanism that clearly warns against harmful behavior promotes the continuation and continuity of life.
From the perspective that animals are given for the use of man, the warning stimuli of pain promote animal survival so they didn't all die off in the first generation, but instead continue to provide sustenance and resources to man on through time.
From the perspective that animals are also on an eternal journey (to be sure, one that differs from the journey humans are on), pain provides protection that promotes the survival of the species, so more animals can obtain physical bodies and progress on that journey that runs through--but does not end with--mortal life.
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Suffering vs. pain
I've focused on pain because suffering is a somewhat murkier term. Certainly "pain" and "suffering" are often used as synonyms, but when we think of human suffering, we generally have something more in mind than just the conscious experience of pain. Fiction which portrays animals exhibiting the full array of conscious thought & experience of humans is misleading. E.g. Finding Nemo tells a great story with valuable lessons, but empathizing with a clownfish (because it is portrayed experiencing human emotions) to the degree that one believes clownfish should have the same rights as humans, is simply confusing fantasy with reality (in any event, the justification for human rights being unique to humans is not our level of cognitive development, but our identity as the offspring of God. Humans with cognitive impairment are just as deserving of human rights).
If suffering is understood to include at a minimum being in pain AND being aware that one is in pain, it is difficult to definitively assess the degree to which animals experience suffering. "Self-awareness" is the variable often used to distinguish between pain and this type of suffering (see discussion here). Some animals do appear to be self-aware; most animals do not (dolphins, elephants, and some primates are strong candidates for self-awareness, but this is not conclusive).
This is not to say animals do not experience pain. A dog and a human exhibit remarkably similar physical and physiological responses to being burned. But psychologically, there is more happening for the human. Thus, some philosophers have defined a distinction between pain (experienced by humans & animals) and suffering (unique to humans and potentially a few animals). I don't believe there's enough data to take a dogmatic position on this issue, but I acknowledge the reasons for distinguishing between pain and suffering.
It does appear that humans are capable of suffering to a degree that most/all animals are not.
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Eternal perspective
One of the most common responses to the existence of human pain is that it is a momentary part of a journey that leads somewhere far better. Experiencing misery (briefly) allows one to prize its absence. If animals have an afterlife characterized by felicity, this response can be applied to animals as well.
Like all of us in this fallen world, animals experience pain. The pain that does not make sense when all we can see is the window of a few years over which it was spread, is cast in a very different light and takes on a different magnitude when the denominator is eternity.
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Death Prior to the Fall
Does believing that evolution of life over many eons is probable require accepting that there was death before the Fall? Not necessarily.
Sections 2 & 3 in this post consider scenarios in which this would not be the case. I do not claim to know the answer on this one, I just don't see any inherent contradiction between a) God created a world in a paradisiacal state without death, and b) after the world exited that paradisiacal state mortal life developed in stages over a number of years (which number may have been large enough that it would have been both meaningless to Moses and impractical for him to try to write it down).
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Conclusion
This mortal life is worthwhile--even for animals--because it is not the destination, it is a step in the journey. If evolution was an effective means to generate progress in that journey, in which temporary pain opened the door to eternal felicity, it is not irreconcilable with a loving God.
