Paleoecology has been an aspect of paleontology since the earliest days of the scientific study of fossils as people sought to understand what the world might have looked like across geological timescales. What did a brontosaurus eat? What did a forest of tree ferns look like? Viewed through that lens, paleontology combined with ecology, climatology, and biology gives us a powerful means of understanding our environment's history. When we start taking underlying geology and overlaying it with past climates, we provide a window into how ancient communities adapted (or not) and came to be in the present day. They expanded or contracted, shifted spatially, and changed their specific composition as time passed.
If you start digging (literally) around in New Mexcico's history, you discover that things were much more mesic back in the day... say, 12,000 years ago. Here's the Pleistocene map side-by-side with an admittedly low-resolution modern vegetation map.
As the last ice age passed and the world grew more clement (from a human's point of view), the alpine areas retreated to above 12,000' and mixed conifer forests shrank right behind. Most obviously though, large areas of yellow pine, aka, Pinus ponderosa, aka Ponderosa pine, insinuated themselves between the piñon-juniper forests and the spruce-fir mountain tops.
As New Mexico warmed, it also dried out. What is now the Chihuahuan Desert contains a large number of landlocked basins. What were once lakes, now became ephemeral playas and salt lakes, depending on what sorts of minerals were brought down out of the geological formations in the surrounding watershed.
And speaking of minerals in the nearby geological formations, limestone layers lifted from seas millions of years old, gypsum beds from long lost mineral-rich marine environments, granite outcrops from ages before the dinosaurs, and basaltic outpourings from many millions of years ago, all contribute to New Mexico's diversity. From these layers, soils of marvelous complexity have been derived.
These edaphic pockets have led to many speciation events in New Mexico. The high levels of endemism we have here are due to the complexity of the environmental matrix: temperature ranges, moisture regimes, soil types, and vegetative history. If you want to find a species new to science and maybe get immortalized with a specific epithet of your very own, the places to look are these weird, isolated habitats with odd soils.
When we toss in human interaction, both pre- and post-1598 (Juan de Oñate's arrival in NM), we add still more variable to the environmental matrix. Once transoceanic vessels began carrying cargo to the New World, it became a foregone conclusion that invasive species would arrive from other continents. From that point on, we've been mucking around with the natural environment in a much accelerated way.
I've just finished reading an article on range size and extinction probabilities (https://onlinelibrary.wiley.com/doi/full/10.1111/geb.13003). Their conclusion:
Although it is expected that species with smaller ranges will be more vulnerable to global extinction from habitat loss than widespread ones, because the drivers of threat are more likely to affect the entire range of these species, we emphasize that there is a lack of studies that quantify this expectation at different spatial scales. Here, we find that relatively small-ranged species are more vulnerable to extinction from habitat loss even at a local scale. This will necessarily cause a disproportionate effect of range size on the risk of extinction at broader spatial scales. Understanding and quantifying the mechanisms that determine local extinction risk from anthropogenic change, how these depend on spatial scale and how local extinction risk, in turn, can be used to predict the consequences of range loss will be imperative for the conservation of species.
The bottom line is that New Mexico's geography, geology, climatology, and history have conspired (in a manner of thinking) to produce a state where we have lots of small-ranged plants that are very diverse yet threatened. Even wide-ranging plants are often only found in localized pockets, for example, cienegas or gypsum outcrops. Scale becomes important in assessing threats.
Here's a map from NatureServe (https://explorer.natureserve.org/) published in the NY Times last week. They've overlaid landuse, in particular, protection status, with the number of endangered species. The result is a glimpse at the general state of play in terms of conservation status.
The Grey Lady had other maps that showed the distribution of endangered or imperiled species at the national level. New Mexico has lots of red splashed over it, which is not necessarily a good thing.
There's a lot going on here, so I'll just leave this for the moment. Suffice it to say, biodiversity isn't as straight-forward as one might think. In an up-coming essay, I'll return to how people are coming up with these maps. Then I'll do a deep dive into the spatial distribution of NM's rare and endangered plants.
More to come.
