Native-Alien Species Boundary / 原生外來邊界

Definition

Native-alien species boundary is the ecological and historical line used to decide whether a population belongs to a place by evolution or natural dispersal, or arrived outside its natural range through human action.

Current Synthesis

The Duanwen episode uses Taiwan mynas to show that this boundary is necessary but not self-executing. Classification requires a time baseline, a spatial unit, a route of movement, and sometimes a judgment about how far historical human activity matters.

The boundary becomes politically and ethically important because it can be mistaken for a moral division. The source distinguishes classification from harm: alien status describes origin, while invasive status requires evidence of negative ecological, economic, health, or safety effects.

Key Claims

• Native and alien status are relative to chosen time and space boundaries.
• Human-mediated movement is central to alien-species classification, but historical records and migration baselines can be ambiguous.
• Invasive status requires demonstrated negative effects, not alien origin alone.
• Classification should support concrete risk assessment rather than enemy-making.

Evidence

• Definition evidence: 「人人喊打」的八哥，與台灣的「外來物種」難題 lays out native, alien, and invasive definitions.
• Boundary evidence: 「人人喊打」的八哥，與台灣的「外來物種」難題 notes that baselines can vary from pre-human modification to pre-colonial or longer ecological timescales.
• Taiwan evidence: 「人人喊打」的八哥，與台灣的「外來物種」難題 contrasts clearly introduced common and white-vented mynas with the more historically debated crested myna.

Counterevidence & Qualifications

Some cases are much clearer than others. The episode treats common myna and white-vented myna in Taiwan as clear alien species, while using crested myna and regional white-headed bulbul movement to show boundary complexity.

What Changed

• Created the classification-boundary concept from the Duanwen myna episode.

Related Concepts

• Invasive Species Management - management field that depends on classification but cannot stop at classification.
• Invasive Species Moralization / 外來種道德化 - failure mode when classification becomes moral ranking.
• Bird Dispersal Ecology - natural movement context for species-range change.
• Urban Ecology - human-modified habitat context that can shift species distributions.