You have a herbivore and a carnivore. If there is no carnivore, the herbivores eat themselves into starvation and cease to exist. If there is no herbivore, the carnivores starve and no longer exist. Both are interdependent on the other to sustain their relationship and the wider ecosystem of relationships they participate in. There are contradictions in that interdependence, places where resource scarcity and social conflict favour the needs of one group over the other. These contradictions will mount- drought driving waterway changes driving vegetation distribution driving caloric availability and shelter- until there’s a catastrophic rupture. Suddenly the population of rabbits stalls and the foxes have nothing to eat. Either new relationships are formed to meet the needs of those former intertwined groups, the groups in their current state die out, or their relationship finds a new equilibrium. As you study how the natural resources drive those interconnected relationships in the ecosystem, you’re doing dialectical materialism. As you study that change over time you’re doing historical materialism.