Variability in the estimation of ungulate group sizes complicates ecological inference

Area of Science:

• Ecology
• Evolutionary Biology
• Animal Behavior

Background:

• Adaptive social behavior in animals is studied in relation to group living costs and benefits.
• Animal groups are key units in ecology and evolution, but definitions of group size are subjective and variable.
• Lack of investigation into the extent and implications of variability in animal group size estimation.

Purpose of the Study:

• To assess prevailing practices in determining ungulate group sizes.
• To examine variability in spatial and temporal definitions of ungulate group sizes.
• To provide recommendations for improving consistency in ungulate group size estimation.

Main Methods:

• Conducted a literature review of 171 peer-reviewed studies on terrestrial Cetartiodactyla and Perissodactyla (ungulates) published between 1962 and 2018.
• Analyzed group size definitions, including spatial (nearest neighbor distance) and temporal extents.
• Examined group size data for 61 ungulate species.

Main Results:

• Observed considerable variability in spatial estimates (1.4m to 1000m nearest neighbor distance), weakly correlated with ungulate body size.
• Found even broader variability in temporal extents, ranging from 3 minutes to 24 hours.
• This variability complicates study comparison, replication, and evaluation of group living theories.

Conclusions:

• Variability in defining ungulate group sizes hinders scientific progress.
• Researchers should clearly describe spatiotemporal extents used for group size definition.
• Standardizing these extents will facilitate cross-system comparisons and hypothesis testing in animal sociality.