A methodological roadmap to quantify animal‐vectored spatial ecosystem subsidies

Abstract

Ecosystems are open systems connected through spatial flows of energy, matter, and nutrients.Predicting and managing ecosystem interdependence requires a rigorous quantitative understanding of the drivers and vectors that connect ecosystems across spatio-temporal scales. Animals act as such vectors when they transport nutrients across landscapes in the form of excreta, egesta, and their own bodies. Here, we introduce a methodological roadmap that combines movement, foraging, and ecosystem ecology to study the effects of animal-vectored nutrient transport on meta-ecosystems. The meta-ecosystem concept -the notion that ecosystems are connected in space and time by flows of energy, matter, and organisms across boundaries -provides a theoretical framework on which to base our understanding of animalvectored nutrient transport. However, partly due to its high level of abstraction, there are few empirical tests of meta-ecosystem theory, and while we may label animals as important mediators of ecosystem services, we lack predictive inference of their relative roles and impacts on diverse ecosystems. Recently developed technologies and methods -tracking devices, mechanistic movement models, diet reconstruction techniques and remote sensing -have the potential to facilitate the quantification of animal-vectored nutrient flows and increase the predictive power of meta-ecosystem theory. Understanding the mechanisms by which animals shape ecosystem dynamics may be important for ongoing conservation, rewilding, and restoration initiatives around the world, and for more accurate models of ecosystem nutrient budgets. We provide conceptual examples that show how our proposed integration of methodologies could help investigate ecosystem impacts of animal movement. We conclude by describing practical applications to understanding cross-ecosystem contributions of animals on the move.

Landscapes shaped from the top down: predicting cascading predator effects on spatial biogeochemistry

“…1). Evaluations will need to test spatially explicit hypotheses by directly linking ecosystem measurements with animal movement data (Ellis‐Soto et al 2021). Specifically, the hypothesis could be tested by comparing soil and plant nutrient data at carcasses (sensu Bump et al 2009a, Keenan et al 2018) versus at non‐carcass sites.…”

“…Furthermore, remote sensing techniques are becoming ever more sophisticated, enabling real‐time tracking of animal movement (Harvey et al 2016, Wilmers et al 2016, Steenweg et al 2017) and hyperspectral analysis of plant and soil properties (Asner and Vitousek 2005, Wang et al 2009). These new tools can and should be combined to conduct research on the relationship between animal movement and biogeochemical cycling (Ellis‐Soto et al 2021). By combining experimental studies with large‐scale, landscape‐level observations, researchers should be able to uncover how interactions between predators and prey can play a role in shaping the spatial heterogeneity of the ecosystems they inhabit.…”

Effects of ungulate density and sociality on landscape heterogeneity: a mechanistic modeling approach

“…While eventually any system would become nutritionally limited without nutrient inputs from some source, or simulations reveal that ungulate populations in nutritionally homogeneous environments may not be as resilient if the ecosystem is a nutritional source rather than sink. This has interesting implications when animals act as vectors of nutrient translocation (McInturf et al 2019, Ellis‐Soto et al 2021) and particularly for caribou, as the majority of populations of caribou are in (Vors and Boyce 2009). Indeed, our modeling suggests the lack of biogeochemical hotspots may be a contributing factor of ungulate population declines in nutritionally homogeneous environments.…”

“…More recently, studies have begun investigating the direct effects of ungulates on nutrient spatial patterns via resource inputs, focusing on the types of nutrients deposited, rates of nutrient recycling and ecosystem productivity at the local scale (Frank and Evans 1997, Coetsee et al 2011, Sitters and Andriuzzi 2019, Subalusky and Post 2019). However, the cumulative effects (grazing and nutrient inputs) of ungulates on nutrient redistribution at the landscape scale remain less well studied (Augustine et al 2003, Seagle 2003, Sitters et al 2017, Veldhuis et al 2018, Ellis‐Soto et al 2021) and currently, there is no consensus regarding the impacts of large ungulates on landscape dynamics (Monk and Schmitz 2021).…”

Patchy indirect effects: how predators drive landscape heterogeneity and influence ecosystem dynamics via localized pathways

“…Nutrients transported by animals are deposited at different rates, locations, and directions (i.e., against natural gradients) compared to passive resource subsidy sources (McInturf et al 2019;Subalusky & Post 2019). Animals that transport nutrients are therefore drivers of landscape-scale patterns in nutrient cycling and storage (Schmitz et al 2018;Ellis-Soto et al 2021), and predators are particularly important subsidy vectors because they transport by carrying them by mouth or in stomachs prey remains high in limiting nutrients (e.g., calcium, nitrogen, phosphorous) (Schmitz et al 2010;Monk & Schmitz 2022). When predators concentrate nutrients derived from prey remains (prey-derived nutrients) into certain areas, they can generate biogeochemical hotspots with patchy effects on other species.…”