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| The subalpine fir has a mutualistic relationship with belowground fungi. Photo Credit: Khilav Majmudar, University of Minnesota |
Scientific Frontline: Extended "At a Glance" Summary
The Core Concept: Mutualism is a cooperative interaction where species exchange benefits to aid each other's survival, such as nutrient exchange between plants and fungi. Recent research analyzes how this dependence influences the ability of non-native species to invade new environments.
Key Distinction/Mechanism: Unlike general competition or predation models, this research utilizes integro-difference equations (IDEs) to simulate how "mutualism dependence"—the degree to which a species relies on a partner—impacts range expansion. The findings indicate that while moderate dependence can accelerate invasiveness, supporting too many partners creates a high metabolic cost that can actually halt an invasion.
Major Frameworks/Components:
- Mutualism Dependence: A metric defining the extent to which a species relies on a partner for growth.
- Obligate vs. Facultative Mutualists: A classification distinguishing between species that are highly dependent (obligate) versus those with lower dependence (facultative) on their partners.
- Integro-difference Equations (IDEs): Mathematical models used to project spatial growth and dispersal patterns over long periods.
- Invasional Meltdown: A theoretical feedback loop where mutualists accelerate one another's invasion, hastening native extinctions.
Branch of Science: Ecology and Environmental Science.
Future Application: Conservationists may use these models to identify specific mutualist partners, such as soil fungi, that facilitate plant invasions. Targeting these partners for biological control could slow the spread of invasive species.
Why It Matters: Invasive species drive the extinction of native flora and fauna; understanding the specific "tipping points" of mutualistic relationships allows scientists to prevent rapid ecosystem collapse known as "invasional meltdown."
Cooperation between species to help each other's survival is known as mutualism. It is seen among many types of organisms, such as plants and fungi that exchange nutrients with one another, plants that provide bees with nectar in exchange for pollination, and sea anemones that provide protection for clown-fish in exchange for excreted nutrients. Recently, scientists have found evidence that some invasive plants become even more invasive in the presence of helpful partners, as can happen with certain pine trees and fungi or fig trees and wasps. But other studies have suggested that species that didn't rely on mutualist partners were more invasive.
Recent research at the University of Minnesota, published in the journal Ecology, attempted to identify the conditions under which a mutualistic partner could make a species more or less invasive. To study this, they built mathematical models called integro-difference equations (IDEs). IDEs take into account the effects of mutualism on growth and dispersal of species and are useful tools to model spatial processes. Mathematical models are helpful in understanding ecological processes like invasion that occur over many years and can be difficult to study in the field.
The team modeled a phenomenon called mutualism dependence, which measures how much a species depends on benefits from its partner for growth. Highly dependent species are often called 'obligate mutualists' and lower dependent species are called 'facultative mutualists.' They then tried to understand how the invasive ability of a species varied as a function of its dependence on its partner.
The research found that:
- Based on how much nutrition (or other benefits) a partner provides, being more or less dependent on a partner could increase a species' invasiveness, as measured by its range expansion speed.
- Having too many partners could stop a species' invasion, as there is a large cost associated with supporting them.
- Mutualistic dependency modifies a species’ spatial distribution, impacting whether it is more populous at the edges or center of its range.
- As invasive species become more widespread, this research could eventually help protect native habitats from mutualistic invaders. Understanding the mutualistic properties of an invasive species could help researchers identify ways to slow the invasion.
“Understanding the role of mutualisms is critical to preventing ‘invasional meltdowns’ which is a process by which mutualists accelerate each other's invasions in a positive feedback loop,” said lead author Naven Narayanan Venkatanarayanan. “Invasional meltdowns greatly speed up extinction of native species and communities. Future applications of this research include identifying and biologically controlling populations of mutualist partners of the invasive species, such as fungi.”
Reference material: What Is: Mutualism | Invasive Species
Funding: This research was supported by the National Science Foundation.
Published in journal: Ecology
Title: Mutualisms impact species' range expansion speeds and spatial distributions
Authors: Naven Narayanan, and Allison K. Shaw
Source/Credit: University of Minnesota
Reference Number: es101923_02
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