The species is an important unit of conservation.

• Major legislation such as the Endangered Species Act (ESA) (CITES)
• Most people have an intuitive sense of what a species is, and can name quite a few.
• Compared to an ecosystem, a species is a relatively well-defined entity

However, many are unaware of the ambiguity in defining species.

Typological vs populational viewpoints

Definitions of Species

Biological species concept: "a species is a group of actually or potentially interbreeding individuals, which are reproductively isolated from other such groups."

difficult to use when species are geographically disjunct, for fossil species.

Morphological species concept: groups of morphologically similar individuals that can be clustered and distinguished from other such groups.

does not distinguish sub-species from species, could result in species status for every population.

Speciation in animal populations requires geographic isolation to create reproductive isolation

Understanding speciation helps us to think of species as reproductive units. This is why many biologists today favor the biological species concept. For further discussion see the speciation lecture of Global Change I

A Digression: What does speciation tell us about the geographic distribution of biological diversity?

Latitudinal gradients: more species occur in the tropics because speciation rates are higher, or extinction rates are lower, compared to higher latitudes. Re-examine the four reasons given last lecture for latitudinal diversity gradients, and you will see these refer to the balance between S and E.

Hotspots: likewise, hotspots must be locations that favor species formation, or species coexistence (less extinction). High habitat heterogeneity for a given area likely accomplished both.

Endemism: oceanic islands (and isolated lakes) have a higher proportion of endemics than land areas of the same dimensions. Colonization is a rare event, and subsequent speciation is likely due to isolation and unique island conditions.

What taxonomic level should conservation focus on?

Population? This is the actual evolutionary unit; genetic diversity and evolutionary potential of species resides in their multiple populations, each somewhat different genetically, and perhaps adapted to local conditions. But there may be several, ten’s, even thousands.

Species? This is the legally defined unit, and a useful "marker" – to be monitored. But is there are 30 million species, can we base conservation on a species approach? In addition, family-level diversity may be more fundamental in terms of body plan diversity.

Of 492 listings under the ESA from 1985-91, 80% were full species, 18% were subspecies, and 2% were populations.

Ecosystems? This seems more practical – protect species and their habitats; not just one species, but many; not when on the verge of extinction, but before seriously threatened. But the definition of ecosystem boundaries is difficult, and the implication that species matter less than ecosystems is troubling.

Two contrasting views:

Hughes, Daily and Ehrlich examine the extinction of populations rather than species. They suggest that while the median estimate for the world’s species is 14 million, the number of populations could exceed 3 billion. Relating population extinction to habitat loss, they estimate the loss rate at 1800 populations per hour (16 million/yr).

Nee and May examine the entire tree of life, and ask how well the tree itself can survive species deletions. If clumps of species get the chop, whole clades could be eliminated. If species extinction is random with respect to taxonomic groupings, much of the "real" diversity – what we see at the family level – will survive. As much of 80% of the basic tree can survive even if 95% of the species are lost.

Is speciation over?

Not in general, but for some organism groups – perhaps. Species formation is more likely to occur when species are widespread, as semi-isolated populations, experiencing different local environments. Species reduced to one or a few populations, in only a few locales (perhaps heavily managed), may be less likely to speciate.

SOME USEFUL DEFINITIONS

Taxonomy: naming of organisms, hierarchical grouping by suites of characters to discriminate among and between groups.

Taxon: unit of study (species, genus, etc.) and unit of taxonomic hierarchy.

Systematics: the logical, orderly presentation of relationships among taxa, with the intent of determining evolutionary relationships and sequence.

Phylogenetic tree: depicts the evolutionary relationships among a group of organisms, based on the pattern of ancestral and derived characters.

Characters used: morphological, genetic, behavioral, fossil.

Ancestral Characters: characters shared within a group because all members of that group share a common ancestor, and posses the trait for that reason.

Derived Characters: characters derived more recently, within one lineage of a sub-group, and not seen in other sub-groups.

Monophyly: all organisms in a group share a single, common ancestor.

Clade: a monophyletic group, which demonstrated that one has correctly discriminated ancestral from derived characters, and avoided incorrect identification of ancestral characters.

Homoplasy: refers to characters which are similar due to convergent or parallel evolution.

Polyphyly: organisms in a group are derived from more than one ancestor. Re-do your analysis (if you realize this has occurred), or acquire more dat

Links:

• The Tree of Life: A multi-authored, distributed Internet project containing information about phylogeny and biodiversity
• World Resources Institute: Another biodiversity web site full of great information.