“Methods and Parameters of Invasive Ecology” by Obi Kaufmann, March 2019
note 1, context: The natural world moves in apprehendable rhythms and cycles that reveal themselves to the scientist and to the artist alike. It is my hope that these distillations of creative and empirical truth, expressed as new, working models and supported by sound theory, serve as tools to better understand the beauty of these ecological concepts. Uniting Invasive ecology and what can be called Disruption ecology, with both Conservation and Restoration ecology, I want to map the unifying systems that govern the bedrock of all living networks.
note 2, reference: these essays make reference to other works that will appear in published works to come, so please disregard specific reference to contextual elements, posted here that make reference to other content tables and source, most obiviously Diagram 1 being referred to as 04.02 and Diagram 2 being referred to as 04.03.
note 3, locality: While these accompanying essays make specific reference to examples in California, the two diagrams are meant to present universal, ecological principles, regardless of locality.
note 4, the adaptive cycle; the pattern of growth, conservation, release and reorganization that governs the life patterns of spatial ecology (ecography.) All living networks share the same adaptive cycle regardless of scale. New growth always evolves into mature forms of conservation within the system-body. This inevitably leads to a release of stored enery at the opposite side of the diagram from the generation of it. The decimination releases resources that make way for the reorganization of those structures. -Obi Kaufmann
When I reference a singular, identifiable, and healthy ecosystem, I mean that it subscribes to a working adaptive cycle, and optimally utilizes all the biotic and abiotic resources present at its disposal to push towards a state of equilibrium. It is equally important to examine the systems of evolution that work to undermine and exploit the adaptive cycle and their methods and consequences of disruption and invasion in California and even more generally, in any natural system. All ecosystems are subject to invasion that threatens equilibrium. Equilibrium is not a state that, if subject to any consistent disturbance is held for any amount of time. Invasivity, either the perpetrating agent or the ecosystem defending against it, is any biological exotic that threatens established, native patterns within the adaptive cycle.
Whether we are talking about ancient invasiveness, recent invasions or biological invasions of the future spurred by anthropogenic climate change, all biological change agents employ common strategies to do what they do: altering homeostasis within the adaptive cycle of any given ecosystem, towards their own ends. Instead of, for example, having a map that describes Sudden Oak Death across California, I think it may be more useful to describe the larger system that particular pathogen works in, and thereby I am describing all pathogens. The following two diagrams (04.02 and 04.03) are models of applied generalities. Nature is very complex and very innovative and in the wake of anthropogenic climate change, this systems-thinking author is sure that these diagrams must be incomplete.
Stage 1: tools of invasivity
The methodology used by all invasive species to infiltrate and overtake an ecosystem falls under three basic, evolutionary concept-strategies. To advance its agenda, an invasive may use one, two or all three mechanisms against a native regime.
1a. Increased competitive ability; when introduced to a novel environment, often an exotic species experiences rapid genetic changes because of new selection pressures.
1b. Novel weapons; Introduced species often utilize alien systems of biochemical interaction that are unknown to the endemic systems present.
1c. Disturbance; Invasives can be adapted to, and may influence altered, abiotic regimes, such as fire or flood, and use them to their advantage.
A good example in California of an invasive that used, and continues to use, all three of these tools is the pathogen known commonly as Sudden Oak Death, Phytopthora ramorum. After arriving to California in the mid-1990’s inside of nursery plants from China, (it may have had multiple waves of introduction at multiple ports) Sudden Oak Death quickly spread to epidemic proportions, now having killed millions of trees and devastated about 230 square miles of Tan Oak, Lithocarpus densiflorus, and Coast Live Oak, Quercus agrifolia, forest – although it also infects at least eight other, native tree species. The pathogen, called an oomycete, behaves similarly to a fungus. Upon arrival, a single genotype evolved into at least three or four strands, better adapted to the local forests (1a). It seems that the pathogen then proceeded with its lethal agenda, by utilizing Bay Laurel, Umbellularia californica, to persist through the dry season as Bay Laurel doesn’t die once infected (1b). To make matters worse, the pathogen monopolized on some successive, rainy seasons that boosted its ability to spore and reproduce quickly (1c).
Stage 2: categories of invasive types
All invasive species fall into three categories. Just like in Stage 1, a single species might be one, two or all three types of invasive depending on its evolutionary agenda and the niche it is trying to occupy. These categories describe an exotic organism’s relationship role that it is attempting to infiltrate the native ecosystem through.
2a. Predator. A predatory exotic species may infiltrate a native food web on any trophic level. A predatory species is most commonly an introduced animal. Examples include the Northern Pike, Esoc Lucius and the Southern watersnake, Nerodia fasciata.
2b. Pathogens. A pathogenic exotic species may infect vulnerable ecosystem and propagate itself as a disease. West Nile Virus is a mosquito-borne disease that continues to plague California and can infect birds, humans, horses and other animals.
2c. Competitors. A competitive exotic species may employ a tool (see Stage 1) to displace a local endemic from its niche, possibly transforming the ecosystem itself. The whole structure of California’s grassland communities was restructured with invasive plant family-species such as the Bromes, Cheatgrass, Yellow Starthistle, and hundreds of others.
Stage 3: invasive deployment
3a. introduction. This aspect of diagram 04.02 represents a temporal horizon that it utilized by invasive species to carry out their agenda. The introduction of an exotic species may be accidental (rats on a boat), incidental (carried by wind and fire), or intentional (planting forage for domestic animals).
3b. establishment. It is at this stage that the invasive decides to “play nice” with others or not. If the evolutionary decision is made to transform the ecosystem in some, fundamental way it may be considered a harmful invasive. If it doesn’t, it may be on the path towards naturalization.
3c. spread. Depending how the exotic, once established species vectorizes its growth, the effects across the ecosystem can be deleterious, as described in stage 4: ecological consequence, or a new equilibrium may begin to immediately reveal itself, as described in diagram 04.03.
Stage 4: ecological consequence
4a. habitat fragmentation. All ecosystems strive towards equilibrium, it is a function of their community. These four consequences are the disparate results following the spread of an invasive through the different, living tiers of the ecosystem. These consequences are from harmful invasives. They are arranged in no particular order. For example, habitat fragmentation occurs over a medium to large scale when native groups are isolated from one another.
4b. contamination. Contamination of the adaptive cycle within an ecosystem may manifest as alterations to the nutrient cycles or a disturbance regime or even a contamination of genetic material due to hybridization. When the invasive Smooth Cordgrass, Spartina alterniflora, hybridized with the native California cordgrass, Spartina foliosa, in the San Francisco Bay, it quickly spread to previously uninhabited mudflats.
4c. pollution. Biological pollution is when disfunction is propagated within an ecosystem because of the advance of an invasive species. A disfunction is any alteration, or set of alterations, that presents a clear threat to the normal operations of the system. For example, an invasive plant, such as French Broom, Genista monspessulana, is a ubiquitous invasive plant across Northern California. Once established the effects of Broom pollution include threats to local wildlife, degraded range and cropland, increased wildfire potential, reduced water resources and accelerated erosion.
4d. depletion. The robbing from any resource store within an ecosystem is known as depletion. Depletion may result because of any of the other three consequences detailed here. Depletion may involve the lessening of any chemical resource (i.e. The nutrient cycle) or any physical resource (i.e. sunlight) that had previous assisted with the normal functioning of the ecosystem prior to introduction.
The ability for an invasive species, or community of invasive species, to alter the ecosystem they are introduced to, and the resiliency of that ecosystem to withstand the invasion is the crux of invasive ecology. This diagram details three models that represents two sides of this ecological tension and the temporal narrative how the tension is resolved over time. As established in diagram 04.02, invasives have an arsenal of tools at their disposal, and in conditions where invasion is possible, the ecosystem will always be altered. How that ecosystem is altered is dependent on characteristics inherent in the endemic system and how rapidly the invasive species’ consequence can be mitigated.
Through these three models, a system of conditions is explored by which ecosystems fight their battle against invasion by assimilation, redefining themselves towards equilibrium – the goal of any healthy, natural community. The first model describes what are the characteristics of vulnerability are that present the ecosystem with the parameters that make it a ripe candidate for invasion. The second model describes what are largely, anthropogenic management strategies to maintain or restore ecological equilibrium. The second model describes the other side of the coin from invasive ecology, the study of conservation ecology. The third model is the battlefield upon which this drama unfolds: time. Given the parameters of model 1, applied to the field of time, will decide how the ecosystem will transform from what it was to it will become once the invasion is resolved.
Model 1: Invasivity parameters within ecosystems
- invasivity. This is the starting point. All the invasive methodologies described in Stage 1 and Stage 2 of diagram 04.02 live here. How they manifest (Stage 3 and Stage 4 of diagram 04.02) is dependent on the five conditions of invasibility within the native ecosystem described in this diagram as surrounding the invasive starting point.
1a. natural enemies. One of the primary factors that control the populations of any exotic species is how, when released into a new ecosystem, they find themselves without the natural enemies of their former environment.
1b. empty niche. It is often simple enough for an invasive to step in for another organism missing from a network and take advantage of resources not currently being utilized. The niche may be empty because of extirpations (See model 3) or because of evolution within geographically separate but physiographically similar environments.
1c. species richness. Species rich ecosystems are more resistant to transformation by invasion than species poor ecosystems. For example, second-growth, timber harvested pine forests are more vulnerable to devastation by a single species of beetle than old-growth forests, rich in conifer diversity that leaves the beetle without a clear vector of single species transmission.
1d. propagule pressure. A propagule is a seed or any means by which an organism reproduces itself. More seeds means a greater likelihood of an established invasion. With increased temperatures over the past one hundred years, we are seeing this kind of invasion take place in high-mountain meadows across the state. Conifers from lower elevations are invading subalpine communities and are launching a campaign of conversion (see Model 3).
1e. highly evolved competition. Habitats that have evolved extremely high levels of competition between organisms for existing resources may be more capable of resisting invasion because of any given organisms ability to out compete a potential invasive.
Model 2: ecosystem equilibrium and management strategies
- equilibrium. This term is used in this diagram as an indicator of a broad condition that all living communities tend toward: the condition by which, the ecosystem realizes an optimal balance of resources in and resources out. An ecosystem in the state of equilibrium is self-perpetuating and is interrupted only by agents that spur succession or conversion (see Model 3).
2a. restoration. Restoration ecology is the science of returning a disturbed ecosystem back to a state of equilibrium that it was in prior to disturbance, either by a biologic invasion or other agent, i.e. fire or flood. Restoration ecology is reactive, where Conservation ecology is proactive and whose general practice is described in the following for methodologies.
2b. prevention. Inhibiting a vector of change is the most successful and cost-effective strategy for the management of change agents. There is a litany of preventative techniques at work across California, from the governmental policy of inspection on the transport of potentially invasive species through to the prescription burning by the Forest Service to maintain a healthy adaptive cycle.
2c. DRE – early detection, rapid response, and eradication. As early in the deployment stage (diagram 04.02 stage 3) an invasive species can be surveilled, the possibility of its successful failure for either conversion or succession will be determined. This can be a difficult process, as it is important to not also destroy any native organism within a similar niche. The eradication of Black rats, Rattus rattus, who threatened shorebirds and their ecosystem on Anacapa Island in 2002, was successfully carried out with the concurrent effort to preserve the native Anacapa deer mouse, Peromyscus maniculatus anacapae.
2d. long-term control and management. Long terms efforts to minimize naturalized species can be as intensive as they are expensive. Mediation is the strategy for some invasives that may be, either providing some established service, or exist on such a scale that eradication is impossible. Controlling feral pigs by hunting and timed grazing to control invasive weeds are two examples of ongoing strategies to control the spread of destructive invasives.
2e. biocontrol. Biocontrol is when another species is introduced to prey upon an already ravaging invasive species and the threat of the second species’ presence is deemed less of a threat than the first’s continued spread. For example, St. John’s Wort, Hypericum perforatum, a poisonous plant to grazing cows, was successfully mitigated in Siskiyou county in the 1950’s by the introduction of Chrysolia beetles that eat the weed.
Model 3: invasive based, ecological transformation
3a. time. Time is the key component that either assures the success or the failure of any evolutionary process. If a change agent, either biological or otherwise, is introduced slowly enough into a ecosystem that is in equilibrium, it may be possible for that ecosystem to absorb that change agent and disarm it efficacy. Heat, with specific reference to anthropogenic climate change, increases that rate at which all reactions occur – whether at the chemical or the ecological level. Speeding up the process of either the rate at which change agents return (i.e. changing the fire or flood regime due as resulted by climate change) or the interval by which ecosystems can absorb any given, invasive threat (i.e. the invasion of exotic grasses through fire distribution,) has the potential to not only fundamentally change the nature of the ecosystem, but (with enough heat, contracting the amount of time for any adaptation) may collapse the whole system itself.
3b. extirpations. Extirpation is when a species is either intentionally or unintentionally made locally extinct. Through competition or displacement between rival organisms, or through non-adaptability with the establishment of some new regime, extirpations are inevitable. Often, a cascading, domino effect forms if the exotic is not able to fulfill the services of the endemic organism, and many species fade away. An example of this in California might be how so many Salmon varieties have been extirpated from their headwater-spawning grounds by dams. This has lead to depletion of nutrients from headwater-forests that has lead to the simplification of the food web in those forests and diminished populations of all types of organisms found there.
3c. naturalizations. A naturalized species is one that has invaded and has been assimilated into the ecosystem, successfully propagating itself, behaving like a native. Naturalization takes successive generations of multiple species-members within the community to determine if the invasion is fundamentally transformative (converted) or not (succeeded).
3d. converted. A converted ecosystem is one that, because of a single change agent, or a series of connected change agents, is destroyed and transformed into a different kind of ecosystem. European grasses, that need to burn every year moving through a forest can transform that forest into a grass land in a relatively small amount of time. A converted ecosystem is defined by the collapse of the adaptive cycle.
3e. succeeded. A succeeded ecosystem is one that, because of a single change agent, or a series of connected change agents, is pushed from one segment of the adaptive cycle to the next. If this procession of succession is not dismantled by the change agency in a short enough period of time, there is a opportunity for that agency to become naturalized and for the ecosystem to realize further equilibrium.
Ecosystems change. It is what they do. By understanding the mechanisms of change can the consequences be mitigated. The idea of equilibrium inside an ecosystem is a state that is only possible in ecological isolation. In the 21st century, ecological isolation doesn’t exist. Humans are the single most destructive invasive species the planet may have ever known. Alas, humans are also the only species to understand the mechanics of invasivity and are potentially able to engage, restore and conserve, valuable ecological networks throughout California and beyond.