Kudzu vs. Honeysuckle: Changing Populations

Kudzu and honeysuckle are two of the most prevalent and well-known invasive plants in the US. We know some key things about how these plants impact the natural ecosystem and their overall range. However, these plants are changing their patterns and population dynamics, evolving to expand ranges, and impacting other species along the way. New studies and information allow for control and management techniques to improve. In this post I will discuss how kudzu and honeysuckle populations are changing and how these changes impact both the environment they invade and those in charge on trying to manage said invasions.

How they’re changing as a population

Kudzu is clearly a highly invasive plant. We see it across the southeast; along highways, in neighborhoods, etc. This invasiveness is due to many different characteristics. One of these is that there is little to no natural predator to this plant in the US. In a 2014 study in China, a team of researchers took kudzu specimens from the invaded Southeast US and specimens that were from the native populations of China. In this study they found that the invasive plants had much lower resistance to herbivory in China than the native Chinese plants (Yang et al., 2014). This supports the idea that the invasive species has evolved in its new range without the need to be resistant to any predators. We all only have so much energy in a day to do the things we need to do. Plants are no different; because invasive kudzu does not give energy to herbivory resistance, it can spend this energy in areas like growth and reproduction.

Figure 1: This figure was taken from Yang et al. 2014. It demonstrates that invasive kudzu in the US were less resistant to herbivory than the native plants in China. This shows that the invasive species have potentially evolved to lack this resistance due to the lack of natural predator in the US.

Figure 2: This figure is pulled from Yang et al. 2014.  It demonstrates the higher overall biomass of the invasive kudzu from the US. In comparison to the native Chinese individuals, the invasive plants showed significantly higher biomass, both aboveground in the stems and leaves, and belowground in the roots.

In addition to this evolution to live without predators, kudzu is able to grow amongst and with those kudzu plants that are genetically unique (Kartzinel et al., 2015). This ability to intermix with genetically variable plants allows kudzu to remain genetically variable while continually growing as a population. According to Kartzinel et al. 2015, this information means that some of the most common management tools for kudzu (mowing, cutting, etc.) may inadvertently be increasing genotypic diversity.

As for our other species of interest, studies have found that invasive honeysuckle growing near the margin of its habitat (rather than at the core of its invaded area) show signs of higher fitness and survival (Figure 2 & 3) (Kilkenny & Galloway, 2015). In terms of invasiveness and population success, this is a key finding. If a plant can spread to the borders of its habitat and have even greater success than at the heart of the population, this will inherently allow for more expansion. For invasive species like kudzu and honeysuckle, this ability allows for further invasion and species success.

Figure 3: This figure is pulled from Kilkenny & Galloway, 2015. It demonstrates the improved fitness of honeysuckle individuals at the margins of the invaded area. This figure gets at the idea that invasive species could potentially benefit from spreading into new habitat, and even show higher survival rates at these outer barriers.

How these changes are affecting the ecosystem

With the spread of these invasive plants due to their continued evolution to better succeed in their environments, the impacts of these plants also become more widespread. For instance, kudzu has been shown to create less diverse communities in the areas it invades. It is an over-arching vine that shades and negatively impacts most other plants in its path. Similarly, both honeysuckle and kudzu have been shown to have negative impacts on trillium plants (a genus of plant native to much of eastern North America) (Heckel, 2004). Trillium species are a commonly studied plants because the genus has both wide-spread and rare species. This dichotomy allows researchers to compare closely related organisms with very different habitat expanses. Regardless of this variation, it has been shown that both of these invasive plants negatively impact any trillium population.

Not only do these plants impact other plants negatively, there are impacts to those animals that use resources from said invasives. For example, there was a fly species discovered that has genetically evolved from a hybridization of two species in response to a new ecosystem invaded by honeysuckle (Carroll, 2007). These flies fed on the honeysuckle to the point that they became genetically distinct from related flies and have now been deemed the Lonicera fly (after the scientific name of honeysuckle: Lonicera japonica).

On to a more charismatic fauna, white-tailed deer have been shown to be a seed disperser for honeysuckle (Guiden et al., 2015). Many of us have seen white-tailed deer munching on vegetation around our backyards or along a roadside. These deer do not discriminate as to what they eat, especially when that food source has such sweet, sugary nutrients like honeysuckle. Because of its attractiveness to deer populations, these deer eat the fruit of the honeysuckle bush and therefore ingest the seeds along with the fruit. On down the road, the seeds pass through and the deer become a disperser for this invasive honeysuckle plant. The form of dispersal is effective and yet another reason why honeysuckle is such a highly invasive species.

How we can manage these changes and impacts

So, we know how invasive these plants are. We know that they are able to change their population dynamics and evolve to better survive in new territories. Now what do we do with this knowledge and how can we implement better management? Researchers are always on the lookout for better tools for management. An example of this innovation is found in an article published that introduced a new model that simulates how invasive plants can be managed best by looking at particular species characteristics. The researcher’s example work was done with kudzu and demonstrated the ability of the model to assist with management and control methods (Aurambout & Endress, 2018). With knowing things about the species biology and dispersal along with local management practices, the model finds solutions at local and regional scales and these solutions “can be compared to identify those most effective given the level of available resources” (Aurambout & Endress, 2018). This is just one example of work being done to better understand and control these invasives.

As for ourselves, how should we think about these invasive plants in our lives? A 2011 article from the US Department of Agriculture nicely summarizes how human activities can increase invasive success (Li et al., 2011). Invasive species are known to take advantage of newly disturbed habitat. This can be related to new residential developments, infrastructure, and industries. Kudzu is a great example of this invasive tactic. Keeping this in mind, it is always a good thing to disturb the natural ecosystem as little as possible. While we may not be able to control the building of new roads or apartment complexes, we can at least keep in mind that invasive preference for these disturbed habitats is just another reason to avoid human disturbance.

References:

Aurambout, J., & Endress, A. (2018). A model to simulate the spread and management cost of kudzu (Pueraria montana var. lobata) at landscape scale. Ecological Informatics., 43, 146–156.

Carroll, S. (2007). Natives adapting to invasive species: ecology, genes, and the sustainability of conservation. Ecological Research, 22(6), 892–901. 

Guiden, P., Gorchov, D., Nielsen, C., & Schauber, E. (2015). Seed dispersal of an invasive shrub, Amur honeysuckle (Lonicera maackii), by white-tailed deer in a fragmented agricultural-forest matrix. Plant Ecology, 216(7), 939–950.

Heckel, C.D., "Impacts of Exotic Invasive Vines on the Ecology and Reproduction of the Endangered Trillium Reliquum" (2004). Georgia Southern University: Electronic Theses and Dissertations. 692.

Kartzinel, T.R., Hamrick , J.L., et al. (2015). Heterogeneity of clonal patterns among patches of kudzu, Pueraria montana var. lobata, an invasive plant. Annals of Botany 116(5), 739–750.

Kilkenny, F., & Galloway, L. (2016). Evolution of marginal populations of an invasive vine increases the likelihood of future spread. The New Phytologist., 209(4), 1773–1780.

Li, Z., Dong, Q., Albright, T., & Guo, Q. (2011). Natural and human dimensions of a quasi-wild species: the case of kudzu. Biological Invasions 13(10), 2167–2179.

Yang, X., Huang, W., Tian, B. et al. (2014) Differences in growth and herbivory damage of native and invasive kudzu (Peuraria montana var. lobata) populations grown in the native range. Plant Ecology, 215, 339–346.