Does probability of occurrence relate to population dynamics?

Area of Science:

• Ecology
• Population Biology
• Biogeography

Background:

• The realized niche defines environments where populations persist with competitors, correlating with positive intrinsic growth rates (r).
• Quantitative links between range-wide demographics and occurrence probability are crucial for understanding species niches and improving distribution models.
• Previous research has not extensively assessed how demographic parameters influence species occurrence probability across diverse regions.

Purpose of the Study:

• To analyze the relationship between demographic parameters (intrinsic growth rate r, carrying capacity K), population density (N), and occurrence probability (Pocc).
• To investigate if these relationships vary based on species' competitive ability, using shade tolerance as a proxy.
• To assess the influence of demographic factors on species' realized niches and geographic distributions.

Main Methods:

• Estimated demographic parameters (r, K), population density (N), and occurrence probability (Pocc) for 108 tree species.
• Utilized data from four temperate forest inventory surveys (Québec, Western US, France, Switzerland).
• Employed shade tolerance as an indicator of competitive ability in forest environments.

Main Results:

• Demographic parameter relationships with occurrence probability showed little variation across shade tolerance levels and regions.
• Intrinsic growth rate (r) was generally negatively correlated with occurrence probability (Pocc).
• Population density (N) and carrying capacity (K) were generally positively correlated with occurrence probability (Pocc).

Conclusions:

• Temperate forest trees exhibit highest occurrence probability in areas with high population density and slow intrinsic growth rates.
• Species' competitive ability (shade tolerance) did not significantly alter the observed demographic-occurrence relationships.
• Uncertainty in demographic estimations necessitates caution when integrating species distribution and demographic models.