---
title: "species, subspecies, and the population in one creek"
canonical_url: https://ensurance.app/guide/species-subspecies-population
markdown_url: https://ensurance.app/guide/species-subspecies-population.md
subtitle: a purpose can zoom in as far as the life does
category: natural-capital
---

# species, subspecies, and the population in one creek

*a purpose can zoom in as far as the life does*

Species vs subspecies, in short: under one common definition, the biological species concept, a **species** is a group of organisms that can interbreed and produce fertile young, kept apart from other such groups. A **subspecies** is a recognized geographic form within a species, a population that looks or behaves distinctly in one part of the range but could still interbreed with the rest. The biological species concept is one of many, and where the lines fall is argued, often hard. Cutthroat trout are a standing example: some sources treat the greenback cutthroat as a subspecies of one cutthroat species, and newer classifications split cutthroat into several species, so even its scientific name differs from source to source.

The law draws its own line. Under the US Endangered Species Act, "species" is a legal category, not only a biological one: "The term 'species' includes any subspecies of fish or wildlife or plants, and any distinct population segment of any species of vertebrate fish or wildlife which interbreeds when mature" (16 U.S.C. §1532(16)).

So one small trout in one small creek can matter to a biologist, to the law, and to the people who keep the creek cold. That trout already exists and already depends on cold water and clean gravel, whether or not anyone names it. **[Ensurance](https://ensurance.app/?from=guide)** is how the purpose you name gets funded to keep working. It is not the trout.

:::johnson
**a purpose can zoom in as far as the life does.** A species, a subspecies, a lineage, one creek: the same account shape holds at every rung.

[see the cutthroat trout account →](/cutthroat-trout.syndicate?from=guide)
:::

## species, subspecies, population: the terms side by side

| term | what it means | who draws the line |
|---|---|---|
| Species | A group that can interbreed, under the biological species concept (other concepts use shared ancestry or distinct traits) | Taxonomists, and they disagree |
| Subspecies | A recognized geographic form within a species | Taxonomists, often case by case |
| Distinct population segment | A population of a vertebrate species that is discrete and significant to the rest of its taxon | US wildlife agencies, under a 1996 joint policy |
| Population | The individuals of a species living in one place and breeding with each other | Field biologists, by survey |

The law already zooms in to one population. A subspecies can be listed on its own. A distinct population of a fish, bird, or mammal can be listed on its own. Pacific salmon are a familiar case, with many runs listed separately rather than as whole species.

## the greenback, from species to one creek

Here is the ladder in one fish, as the sources report it.

**The species.** Cutthroat trout are native trout of western headwaters. The protocol's [cutthroat-trout.syndicate](/cutthroat-trout.syndicate?from=guide), a purpose account with a wallet deployed, describes them as now at a fraction of their historic range, with hybridization, warming streams, and barriers deciding whether pure lineages hold.

**The subspecies.** The greenback cutthroat is Colorado's state fish. It was first listed as endangered and was moved to threatened in 1978, its status as of the agency's last published review. For decades, recovery work stocked fish believed to be greenbacks.

**The lineage.** In 2012 a genetic study led by Jessica Metcalf at the University of Colorado Boulder, published in *Molecular Ecology*, compared modern trout with historical museum specimens. The study reported that greenbacks were native only to the South Platte River basin, that much of the recovery stock was not greenback at all, and that the only pure greenback population left lived in Bear Creek, a small stream on the southwest edge of Colorado Springs, in the Arkansas River drainage, outside its native range. The fish are thought to have been carried there from the South Platte in the late 1800s.

**What later work found.** A 2014 Colorado Parks and Wildlife workshop summary treated the Bear Creek fish as a unique lineage that appears to represent the native South Platte cutthroat, and noted that taxonomic revisions were still needed. Offspring of Bear Creek fish were raised in hatcheries. From 2016 the agency stocked young greenbacks in Herman Gulch, inside the native South Platte drainage, and in September 2022 it announced that those fish were reproducing on their own there, the first of the reintroduced populations to do so. The agency said it would keep stocking.

**One creek.** So the purpose zoomed from a species across the West, to a subspecies, to one lineage, to one stream near a city, and then back out to a second creek where the fish now spawn without help. At every rung someone could name it and keep it. None of this was done by the protocol, and the syndicate does not fund any restocking. Biologists, the state, federal agencies, and anglers did the work.

## the same rungs, as accounts

| rung | example | account in the catalog |
|---|---|---|
| Species, range-wide | Cutthroat trout across western headwaters | [cutthroat-trout.syndicate](/cutthroat-trout.syndicate?from=guide), purpose, wallet deployed |
| A different subspecies in its watershed | Colorado River cutthroat, a different cutthroat from the greenback, which the watershed account's own description names among its residents | [roaring-fork-river.basin](/roaring-fork-river.basin?from=guide), place, wallet deployed |
| Population in one creek | Bear Creek's greenbacks; the Herman Gulch fish | None today; a keeper could [propose one](/agents/create?from=guide) |

Elk run the same ladder at a larger animal's grain. [elk.syndicate](/elk.syndicate?from=guide) holds the species-wide aim, and its own description names winter range in the Roaring Fork and Eagle valleys and around Yellowstone. A herd that winters in one valley is a population in place. [salmon.syndicate](/salmon.syndicate?from=guide) is an address for salmon recovery across the North Pacific and Atlantic, with no wallet yet.

**What stays the same:** the account shape, and the fact that the fish needs cold, connected water at every rung. **What changes:** the evidence (a range map, then a genetic test, then a redd count in one creek), the keepers (a regional coalition, then a state agency, then the people who walk one stream), and the risk (a lineage in one creek can be lost to one fire or one flood).

A species is a purpose that lives in places. That is why the trout account sits on the purpose leg and the creek account on the place leg, and why a population is the purpose in one place. For why a species list alone misses this, read [a species list is a headcount](/guide/a-species-list-is-a-headcount?from=guide). For why the account is not the animal's own, read [can an animal have a bank account](/guide/can-an-animal-have-a-bank-account?from=guide).

## what to take from it

If the law and the science both zoom to one population, a purpose can too. Name the size you actually care about. If it is the whole species, there is an account for that. If it is the trout in the creek behind your house, that creek is a place, the trout in it is a purpose, and you may be one of its people.

Several accounts can serve the same fish. None of them speaks for it, and none replaces the agencies, tribes, anglers, and landowners already doing recovery work. The next post leaves use behind entirely: [some things are kept for no price](/guide/some-things-are-kept-for-no-price?from=guide). If you keep a creek or a run and want it named, [tell us about it](/contact?from=guide&topic=ppp-purpose).

## frequently asked questions

### what is the difference between a species and a subspecies?

Under the biological species concept, a species is a group that can interbreed and produce fertile young. A subspecies is a recognized geographic form within that species that could still interbreed with the rest. Taxonomists often disagree on where the lines fall.

### does the endangered species act protect subspecies?

Yes. The Act defines "species" to include any subspecies of fish, wildlife, or plants, and any distinct population segment of a vertebrate species that interbreeds when mature. The greenback cutthroat trout, a subspecies, is listed as threatened, as of the agency's last published review.

### can one population of a species have its own account?

It can be named as one. On ensurance a species-wide aim sits on a purpose account like `cutthroat-trout.syndicate`, and a population lives in a place, so a creek or watershed account carries it on the ground. No account exists yet for Bear Creek or Herman Gulch.

## sources

[Endangered Species Act, 16 U.S.C. §1532, Definitions (US Government Publishing Office)](https://www.govinfo.gov/content/pkg/USCODE-2011-title16/html/USCODE-2011-title16-chap35-sec1532.htm) — paragraph (16), the definition of "species."

[US Fish and Wildlife Service and NOAA, Policy Regarding the Recognition of Distinct Vertebrate Population Segments, 61 FR 4722, 1996](https://www.govinfo.gov/content/pkg/FR-1996-02-07/html/96-2639.htm) — the discreteness and significance tests for a distinct population segment.

[University of Colorado Boulder, "New CU-Boulder study clarifies diversity, distribution of cutthroat trout in Colorado," 24 September 2012](https://www.colorado.edu/today/2012/09/24/new-cu-boulder-study-clarifies-diversity-distribution-cutthroat-trout-colorado) — on Metcalf et al., *Molecular Ecology*, 2012: museum-specimen genetics, native range in the South Platte basin, the Bear Creek population.

[Colorado Parks and Wildlife, 2014 Greenback Cutthroat Trout Workshop Summary](https://cpw.state.co.us/Documents/Research/Aquatic/CutthroatTrout/2014GreenbackCutthroatTroutWorkshopSummary.pdf) — the Bear Creek lineage as the apparent native South Platte cutthroat; taxonomic revisions still needed.

[Colorado Public Radio, "Colorado's state fish, once considered extinct, is reproducing naturally in native waters," 26 September 2022](https://cpr.org/2022/09/26/colorado-extinct-greenback-cutthroat-trout-reproducing) — Herman Gulch stocking from 2016 and natural reproduction announced in 2022.

[US Fish and Wildlife Service, Final Determination of Threatened Status for the Greenback Cutthroat Trout, 43 FR 16343, 1978](https://www.fws.gov/species-publication-action/final-determination-threatened-status-greenback-cutthroat-trout-0) — the move from endangered to threatened.

[US Fish and Wildlife Service, five-year review notice for the greenback cutthroat trout](https://www.fws.gov/story/2005-12/us-fish-and-wildlife-service-announces-initiation-5-year-review-greenback-cutthroat) — the agency's most recent published review notice found.

## the series

1. [what counts as a purpose?](/guide/what-counts-as-a-purpose?from=guide) — read first
2. [a flow is a purpose](/guide/a-flow-is-a-purpose?from=guide)
3. [an ecosystem is a purpose too](/guide/an-ecosystem-is-a-purpose-too?from=guide)
4. [species, subspecies, and the population in one creek](/guide/species-subspecies-population?from=guide) — you are here
5. [some things are kept for no price](/guide/some-things-are-kept-for-no-price?from=guide)
6. [every purpose needs people who keep it](/guide/every-purpose-needs-people-who-keep-it?from=guide)

## the three series

1. [what counts as a place?](/guide/what-counts-as-a-place?from=guide) — place
2. [what counts as a purpose?](/guide/what-counts-as-a-purpose?from=guide) — purpose
3. [who counts as people?](/guide/who-counts-as-people?from=guide) — people
4. [what do you want to ensure?](/guide/what-do-you-want-to-ensure?from=guide) — where the three began