Mutualisms impact species' range expansion speeds and spatial distributions

Area of Science:

• Ecology
• Evolutionary Biology
• Theoretical Ecology

Background:

• Mutualisms, or mutually beneficial interactions between species, are crucial in shaping ecological communities and population dynamics.
• The degree of partner dependence in mutualisms ranges from complete obligacy to generalist interactions, influencing species' ecological roles.
• While empirical evidence suggests partner dependence affects range expansion speed, a theoretical framework is lacking to explain these dynamics.

Purpose of the Study:

• To develop a theoretical model investigating how mutualisms and varying degrees of partner dependence influence the speed and spatial distribution of species range expansion.
• To identify the conditions under which mutualistic benefits enhance or hinder range expansion rates.
• To explore how spatial dynamics can lead to the formation of species' range limits through mutualistic interactions.

Main Methods:

• Developed a spatially explicit model incorporating the population dynamics of two dispersing, mutualistically interacting species.
• Simulated range expansion across a gradient of dependence, from complete independence to obligacy.
• Analyzed the impact of mutualistic benefit magnitude on expansion speed and spatial distribution.

Main Results:

• Species range expansion speed is influenced by the degree of mutualist dependence, with complete, no, or intermediate dependence potentially leading to maximal expansion rates.
• The magnitude of benefits exchanged in a mutualism can either hinder or enhance the speed of range expansion.
• Different levels of interspecific dependence alter the spatial distribution of expanding populations, and can lead to exploitative interactions and range limits.

Conclusions:

• Mutualistic interactions and partner dependence play a significant role in determining species' range expansion dynamics and spatial distributions.
• Understanding the spatial context of mutualisms is key to predicting species' range limits and overall distributions.
• The interplay between dependence, benefit magnitude, and spatial dynamics can transform mutualisms into exploitative relationships, shaping community structure.