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Welcome to our page. This infographic will walk through various topics relating to biodiversity, ecosystem function, and biological invasions, and how they are occasionally all interconnected. By the end of it, you will hopefully have a better grasp on how to try to answer the question: what are the zoogeochemical impacts of invasive species?

This infographic flows from top to bottom. We begin by providing brief backgrounds on:

1.  The importance of biodiversity
2. The threat of biological invasions
3. The impact of invasive species on biodiversity
4. The relationship between biodiversity and ecosystem function
5. The role of zoogeochemistry in ecosystem function
6. The potential zoogeochemical threats of invasive animals

We finish by discussing our knowledge gap: how can we assess the zoogeochemical impacts of invasive animals? We briefly discuss some innovative, futuristic tools that could eventually be used in a perfect world to address the question. We then provide a brief literature review discussing some current tools that could potentially be used to partially fill this gap today.

Enjoy!

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Biodiversity is extremely important and can improve the resilience, resistance, and function of ecosystems across the globe, as shown in this video.

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Why is biodiversity so important? - Kim Preshoff

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One threat to biodiversity is that posed by biological invasions. Biological invasions are capable of causing considerable environmental change (Vitousek et al. 1996). When established, invasive species commonly thrive and dominate in new ecosystems, profoundly altering native communities (Lowe et al. 2000; Gurevitch et al. 2004). They are considered second only to habitat loss as the leading cause of species endangerment and extinction (Clavero & Garcia-Berthou 2005; Clout & Williams 2009).

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The threat of invasive species - Jennifer Klos

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Global Invasion Threat for the Twenty-First Century

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Global Invasion Threat for the Twenty-First Century

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As seen in the graphic below (Regan et al. 2016), the United States presents some of the highest risk sites for biological invasions. As such, it is especially pertinent to broaden our knowledge of invasive species impacts within the systems they are introduced to.

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Invasive species are considered one of the greatest threats to an ecosystem because of their ability to cause biodiversity loss (Sala et al. 1999; Mainka et al. 2010). At the local level, the introduction of a new species may actually appear to improve biodiversity by increasing the net species richness of the area. However, despite some arguably positive effects on biodiversity at the local level, overwhelming evidence indicates that invasive species have profoundly negative impacts on species and genetic diversity at both the local and global level (McNeely et al. 2001). If we think of biodiversity as a net, when an extinction occurs because of an invasive species, a knot is untied within that net making the ecosystem more fragile and prone to collapse. As such, these introductions can cause severe disruptions of native communities which can in turn lead to a negative influence of the indigenous species’ genetic diversity.

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The Many Drivers of Biodiversity Loss, Including Invasive Species

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The Many Drivers of Biodiversity Loss, Including Invasive Species

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Relationship Between Biodiversity and Ecosystem Function

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Relationship Between Biodiversity and Ecosystem Function

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Ecosystem function reflects the collective life activities of plants, animals, and microbes, and the effects these activities (e.g., feeding, growing, moving, excreting waste, etc.) have on the physical and chemical conditions of their environment (Naeem et al. 1999). Biodiversity is now known to be a major determinant of community and ecosystem dynamics and functioning (Tilman et al. 2014). Biodiversity improves ecosystem function via interspecific complementarity, greater use of limiting resources, decreased herbivory and disease, and nutrient-cycling feedbacks that increase nutrient stores and supply rates over the long term (Tilman et al. 2014). It is well known through numerous studies that highly diverse ecosystems can produce much more than ecosystems that are dominated by monocultures. Crops are a good example of this. Homogenization, sometimes coined ‘biological pollution’, increases the vulnerability of species to both native and exotic pests and disease (McNeely et al. 2001). If we once again think of biodiversity as a net, reducing the biodiversity reduces the number of knots in the net. By reducing the knots in their diversity net, these monoculture systems become more fragile, which can eventually lead to cascading effects on the surrounding ecosystems.

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So, What Is Zoogeochemistry and What Does It Have To Do With This?

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So, What Is Zoogeochemistry and What Does It Have To Do With This?

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Zoogeochemistry aims to examine the effects of animals on the biogeochemistry of an ecosystem (Schmitz et al. 2018). Biogeochemistry is a major facet of ecosystem function, which is closely intertwined with biodiversity. Many direct effects of animal invasions on biodiversity have been thoroughly studied, but many indirect effects remain largely unexplored, including the impact on the biogeochemistry. Biogeochemistry is an interdisciplinary science that aims to examine the chemical, geological, physical, and biological processes that underlie proper functioning of the ecosystem (Schlesinger 2005). Animals play an important role in these biogeochemical processes, as they store, transport, and exchange nutrients across the landscape (Schmitz et al. 2018). These zoogeochemical, or animal-mediated, effects are capable of substantially influencing the cycling of nutrients throughout the ecosystem, which is essential for ecological productivity (Schmitz et al. 2014; Atwood et al. 2015).

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The site below describes some of the various biogeochemical processes and how they can be influenced by hydrology, geology, flora, and fauna.

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Click on elements of the model or select from the tabs below

The hydrology of floodplain tree swamps is related to a site's topography, substrate type and position within the catchment (see Hydrology-landscape Position). Climatic factors (especially those related to rainfall) also play a significant role in the regularity, seasonality, duration and amount of water entering and leaving the wetland.

Water Inputs

Floodplain wetlands can be flushed with water from overbank flow, streams leading directly to the site, sheet flow across the floodplain, rainfall, run-off from the local watershed, hyporheic flow and other groundwater discharge, or a combination of these sources.

If groundwater table levels and substrate permeability permit, this can lead to more constant systems. This wetland habitat type can play a role in groundwater recharge/discharge.

An important point to note is that hyporheic flow and groundwater flow tend be clear (not turbid), compared to surface water flow.

Water Outputs

Evaporation, transpiration and groundwater recharge can lead these systems to dry out, often completely (see dry model).

Overbank floods move out onto the floodplain or back to the channel, connecting the wetland habitat to other wetland habitats in the floodplain. Water may also flow out to the ocean via distributary channels, depending on topography.

Water Quality

More research is needed to demonstrate the effects these wetland habitats have on the hydrology and water quality of the broader system. It is suspected that the water leaving these wetlands, entering other wetlands or returning to streams would have differences in turbidity, Coloured Dissolved Organic Matter (CDOM), acidity, Dissolved Oxygen (DO), conductivity and organic matter. These effects are complicated and site dependent, and could have an appreciable effect on water quality in downstream waterways.

Connectivity

The inlet and outlet of water flow for these wetland habitats can be different. Drainage points can go back into a creek and/or go in another direction, connecting the wetland to other swamps, lakes, streams, estuaries or the sea, and may even break catchments.

Under low or no flow conditions, local factors determine water quality and can act like non-floodplain systems when not hydrologically connected to stream systems.

Hydrology and Vegetation

Hydrology can play an important role in influencing the growth and distribution of vegetation communities. Melaleuca trees can be temporarily inundated with water for three to six months of the year. Areas that are inundated for longer periods tend to shift towards grass, sedge, herb-dominated wetlands. In the Wet Tropics coastal lowlands, annual rainfall is high enough (greater than 3000 mm annually) for palm swamps to grow on very wet, poorly drained soils.
This page should be cited as:
Department of Environment and Science, Queensland (2013) Coastal and subcoastal floodplain tree swamp-Melaleuca spp. and Eucalyptus spp. - Hydrology, WetlandInfo website, accessed 24 September 2020. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/ecology/aquatic-ecosystems-natural/palustrine/floodplain-tree-swamp/hydrology.html

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Coastal and subcoastal floodplain tree swamp-Melaleuca spp. and Eucalyptus spp.

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Click on elements of the model or select from the tabs below The hydrology of floodplain tree swamps is related to a site's topography, substrate type and position within the catchment (see Hydrology-landscape Position). Climatic factors (especially those related to rainfall) also play a significant role in the regularity, seasonality, duration and amount of water entering and leaving the wetland.

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The Zoogeochemical Threats of Invasive Animals

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The Zoogeochemical Threats of Invasive Animals

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As we've learned, invasive animals are capable of impacting local abundances of native species (Wilcove et al. 1998; Parker et al. 1999 ), and occasionally cause severe population declines (Dorcas et al. 2012). In especially extreme cases, such as with invasive Brown Treesnakes (Boiga irregularis) on the Island of Guam, animal invasions can lead to local extinctions (Savidge 1987). The impacts that invasive animals have on local abundances of native populations can potentially disrupt the underlying biogeochemical processes that those native species influence.

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An invasive Brown Treesnake (Boiga irregularis) eating a native white tern (Gygis alba).

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Zebra mussels are a great example of a species that have altered biogeochemical flow in a system. By filtering out large amounts of plankton and detritus from the water column, they alter the nutrient flow by transferring energy to the benthic zone, making more nutrients available to bottom-dwelling species. Expanding on our knowledge gap, this is one species where the nutrient shift's secondary impacts remain relatively unstudied.

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The Knowledge Gap: What Are the Zoogeochemical Impacts of Animal Invasions and How Do We Measure Them? 

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The Knowledge Gap: What Are the Zoogeochemical Impacts of Animal Invasions and How Do We Measure Them? 

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Direct effects of animal invasions, including impacts on local prey populations, are commonly researched and frequently detected. However, further impacts, including indirect effects, are far less studied. Changes in native fauna can cause changes in the trophic ecology of an ecosystem, which can have profound impacts on ecosystem function. Exploring these effects requires deep knowledge and understanding of not only the trophic relationships within an ecosystem, but also the impacts each species has on proper ecosystem function, such as the amount of nutrients each species is responsible for inputting or transporting. This challenge remains unresolved due to the difficulties associated with understanding these relationships.

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With no limitations, we could get a perfect measurement of the biogeochemical impact of invasive species. This is what that might look like:

Drone imagery at the satellite level to census every individual animal in a system, so we have exact measurements of every single individual in a species. We would do this before the introduction of an invasive species, and after.

From there, we would measure the amount of energy and nutrients each individual puts into, and takes out of, a system. An ideal tool would be almost like an x-ray machine, but which breaks down the chemical makeup of the individual. This would be applied to the animal itself, excrement, and carcasses, measuring multiple individuals across all of the species to get averages for each. This includes the invasive species after introduction to the system of interest. It would also scan various aspects of the physical environment, like detritus inputs, soil composition, and water values.

Thus, we would have precise data about how a system changes after exposure to an invasive species. However, the world is not a perfect place... And perfect data are nearly impossible to obtain. As such, we've come up with the following solution.

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Infrared drone imagery of elephants nearing a village...now, envision improving this technology and using it to accurately count each individual in the ecosystem.

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Step One: Tackle the Life History Aspects

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Step One: Tackle the Life History Aspects

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In order to begin addressing the zoogeochemical impacts of an invasive species, first we must understand the life history of that species. This is broken down into a myriad of necessary components:

1. Fecundity
This can be drawn from demographic data, using either number of births per female per unit of time, or the total number of "births" (hatches, etc.) per unit of time.

2. Growth Rates
Notably, through Integrodifference equation (IDE) models to project spread rates (Neubert & Parker, 2004).

3. Survivorship
With this parameter, it is worth addressing the variability in survivorship depending on the system's resistance to invasion and the individual species propagule pressure. Even with high propagule pressure, invasive species struggle to establish in highly resistant (undisturbed) habitat (Barney et al., 2016).

4. Density Dependence
This parameter has complex relationships at the species-to-species level, often displaying significant but non-linear relationships that make analyses challenging (Jackson et al. 2014). However, density dependence can still be utilized in a variety of ways. There is potential to convert a density-impact curve from an economical and management perspective (Zipkin et al. 2009) into a more biogeochemical focus.

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In order to understand biogeographical disturbances in the face of an invasive species, we must first understand the community where the invasion occurs. We can do this through meta-analyses of community composition over time, to garner how the system functions in the absence (and presence) of these invasive species.

Some additional interactions that may shape the system include:

1. Spatial resource allocation, and how this may be used as a means to limit invasive species in the area (Nishimoto et al., 2020).

2. Integration of network scale effects to observe the impacts on Spatially-Structured Populations (SSP's). SSP's have, historically, been ignored in local, patch-scale studies on invasive species impact (Manenti et al., 2019).

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Step Three: Tackle the Biogeochemical Aspects

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Step Three: Tackle the Biogeochemical Aspects

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In order to understand the biogeochemical impacts of an invasive species, the biogeochemistry of the system must be understood.

This can be done by using Lieberg's Law of the Minimum (Kaspari & Powers 2015). Generally, these limiting factors are considered to be Nitrogen and Phosphorous (Vitousek & Farrington 1997).

In order to understand how different species in a system utilize these limiting factors, we must measure nutrient input and nutrient utilization on a species-to-species basis. There is a computational framework to understand this process in monogastric species, requiring inputs on species nutrient intake, fecal and urinary excretion, and production in terms of protein and lipid accretion in order to yield a flow of energy utilization (Birkett & de Lange 2007).  A meta-analysis holds potential to yield this information for various species within a community, and this framework could be extended into ruminants and other similar species in order to grasp the overall flow of energy within a system.

However, there has been research that suggests ratios of energy and material supplies available are density-dependent, and these stoichiometrically mediated interactions have the potential to shape energy exchange within systems (Urabe et al., 2002). In order to accurately portray the system, these variable factors should be integrated into a system-wide framework for analysis.

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This law is visualized by "Lieberg's barrel," in which water droplets in the barrel symbolize the various facets of life within a system. The amount of water, or "life," depends on the barrel's structure (or nutrients in a system). As such, each barrel (system) can only yield as much water as the smallest panel in the barrel (the limiting nutrient).

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The direct effects of invasive species are well studied, but their indirect impacts are often overlooked. Hopefully this project higlighted one such gap in knowledge: their zoogeochemical impact. Invasive species can change how ecosystems function, including altering nutrient flow and impacting overall biodiversity. The question remains- what secondary effects, such as biogeochemical alterations, occur with the introduction of an invasive species?

This is a difficult question to answer. In a perfect world, there would be exact measurements of every individual across every species, so exact inputs and outputs in the environment would be known, but this is impractical. Since this technology is unavailable, the current tools listed are means by which we can currently work to fill in the knowledge gap. Each step will need to be performed for the ecosystem in question. While this may not be an easy task to accomplish, it is an important one. By furthering our knowledge on how invasive species impact ecosystem function, such as alterations to nutrient flow, we will be better prepared to combat the negative impacts they cause in areas already invaded, and potentially better protect areas they have not yet reached.

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