If I am too cold for human friendship, I trust I shall not soon be too cold for natural influences. It appears to be a law that you cannot have a deep sympathy with both man and nature. Those qualities which bring you near to the one estrange you from the other. — Henry David Thoreau 
The idea that two similar species cannot coexist if their ecological niches completely overlap, also called the competitive exclusion principle, or Gause’s Law, lies at the core of the science of population evo-ecology in the same way that Occam’s Razor lies at the core of evolving cultures and languages; but the One Species, One Niche principle also has profound implications for our understanding of Humans and Nature, where the human technological ‘strategy’, by its very nature, subverts this principle.
This is how competitive exclusion, taken to be the organizing principle of the Natural World,  is introduced and it’s evolutionary implications developed in Darwin, Dogen, and the Extremophile Choice:
… the result is not death to the unsuccessful competitor, but few or no offspring. Sexual selection is, therefore, less rigorous than natural selection. —Charles Darwin 
From the ecological standpoint, a species is a population of organisms that can’t breed beyond itself without compromising the ability of offspring to compete for resources or withstand the elements and predators they are exposed to. The genetic traits of a species are generally fine-tuned to a set of resources and conditions that, in the aggregate, define its ecological niche. Since a deviation in these traits means an organism would likely be competing in the awkward area where its niche overlaps that of another species, the natural fact that disadvantaging traits aren’t likely to show up in a next generation ensures that there’s no unnecessary overlap among well-contested ecological niches. This competitive exclusion near the boundaries of a niche establishes what’s called a resource partition, and as long as ecosystems are undisturbed, the forms and behaviours of species will remain within their defining partitions.
But of course ecosystems are not always left undisturbed; sometimes an entire species disappears, leaving resources to spare; and sometimes whole new ecological vistas open up—as maritime or mountaintop ‘islands’. When a species then finds itself largely uncontested, some divergence in its species-normal set of genetic traits can be expected. And once a critical threshold of resource-use disparity has been reached within the niche—where hybrid compromises might be a disadvantage  —the splitting of its genepool, or its adaptive radiation into more efficient resource-sharing strategies, is accomplished very quickly in geological time.
If speciation events can be relatively quick, in geological time, it’s because selection, in its own way, uses ‘two hands’ for raising its partitions. In evolutionary terms, competitive exclusion implies not only that an organism’s immediate prospects must decline if its genetic endowment predisposes it to compete for resources better suited to another species, but its prospects for finding a mate will, by innate sexual preferences, become subject to selection as well. So when we now consider the critical stages of speciation, it should be kept in mind that this double jeopardy is encountered even when an organism competes across racial lines; and it is sexual selection, working directly on DNA ‘bloodlines’, which makes the definitive cut between single-species populations that are already branching due to a more immediate natural selection for the efficient use of resources. (There will be more about sexual selection as ‘definition’ later, but even here you might see how this evolutionary dynamic is similar to the way words define the more behaviourally nuanced concepts in human cultures. See https://www.extremophilechoice.com/2019/12/08/the-real-language-of-nature/ )
Do you see a problem here when human technology enters the mix? By its very nature, technology allows us to compete with all other species! And this competitive exclusion of entire biomes has been accelerating on a hyperbolic curve from the time Homo Sapiens Sapiens first started weaving baskets and flaking stone tools.
So is this an ‘end times’ problem? Or is it a ‘brave new world’ opportunity? Introducing https://www.extremophilechoice.com/wp-content/uploads/2018/12/Download-Quick-Tour.pdf
— a philosophy of Humans and Nature which, in contradiction to Thoreau’s “law”, might allow us after all to “have a deep sympathy with both man and nature”. (If you don’t happen to have time, at the moment, to view the whole presentation, please at least check out pp. 9 and 10 to ‘get straight to the point’ — so to speak.)
1. Thoreau Journal p. 400. Entry 11 Apr. 1852
2. As an ecological principle, competitive exclusion refers mainly to a species’ relationship to resources, and, as such, the principle has been shown in studies to work better in test tubes than it does in authentic ecosystems. This is because many factors in the Natural World come into play that fall outside the strict ecological meaning of ‘resource’; like relationship to croppers and predators (to which the species in question is itself a resource); like geographic range (plankton in the ocean have more opportunity to avoid competition than Gause’s yeast in a test tube); or like variability of conditions (a flash flood can create a carrion boon that the local specialists, i.e. vultures, can’t fully consume). Here I am using the broader meaning, where a species’ resources are the general conditions that favour its speci-fic existence; that is, where all these effects play out in the long term of evolutionary ecology to arrive at the ‘One Species, One Niche’ implications of the principle.
3. Darwin, 1968, The Origin of Species, Natural Selection, p. 136.
4. The original view of speciation assumed a certain degree of geographical isolation between two populations of a single species, which allowed for character displacement, followed by renewed contact; and from here it was supposed that competitive exclusion takes over. Throughout this book I am favouring a view closer to Paul Colinvaux’s (2007, pp. 121-122.) which gives far more credit to the subtlety of co-evolution. Isolation need not be so crudely “geographical” in very large and complex ecosystems. It is still generally assumed that novel traits favouring the exploitation of new resources, at the expense of more species-typical resources, will get quickly diluted by the interbreeding of a large population. But it was demonstrated by Patrick Bateson as early as 1982 (Gould, 1995, pp. 379-380, “The Great Seal Principle”) that sexual selection goes beyond the establishing of overt traits to ensure advantageous mating; and in fact a general rule for perhaps all sexual species is “maximal attraction to intermediate familiarity”. It’s understandable that avoidance of breeding with close family is adaptive, but why is mating with intermediate family more adaptive than mating with more distant relations, unless selection for racial disparity is at play here? Nature seems to have evolved ways to get around even “novelty dilution”, so who are we to insist on a model of speciation simply because it’s crude enough for us to represent?