Understanding The Impact Of Non-Native Species On Native Vegetation

Factors Contributing to the Success of Invasive Species

Non-native species overcome barriers to naturalize and become invasive in introduced range (Cuda et al. 2015). According to Morgan (1998), the Australian native species have developed highly defensive traits. Furthermore, the study has demonstrated the susceptibility of the native vegetation to the remnant of the Australian species found within Eastern and Coastal areas, where the size and nature of the plant species are impacted. Various research findings have revealed that some of the invasive species have a competitive edge to native species (Mack et al. 2000; Vila ` et al. 2011). The invading species negatively impact the functioning of the invaded ecosystem and reduced biodiversity of the native species as suggested by (Pys ?ek and Richardson 2010; Vila ` et al. 2011; Gaertner et al. 2011). Ecological and biological characteristics such as tall structure, great biomass, faster growth rate, great survival, effective dispersal mechanism, and great fecundity have immensely contributed to the success of the invasive species in the invaded ecosystem according to (Pys ?ek and Richardson 2008; Malíková et al. 2010; Van Kleunen et al. 2010). Moreover, the invasive plant species are phenotypically plastic as compared to the native or non-invasive species, hence they can efficiently grow and reproduce in diverse environmental conditions (Berg and Ellers 2010; Ska ´lova ´ et al. 2012), leading to the spread of their habitat niche beyond the invaded range. According to Richards et al. (2006), the plasticity as a morphological characteristic contribute the success of invading plant species by providing ability to optimize fitness in a variety of environment. Studies have been conducted to provide more information into the role of plant plasticity. According to Burns (2004), invading plant species characteristics should be measured in more than one physical environment or under competition.

Different studies have linked the extinctions of the non-invasive species to the invasion by the non-native species (Hui et al. 2016; Gurevitch and Padilla 2004). Furthermore, studies have shown that the invasive plant species is disperse not only in disturbed areas, but also in places where other native plant species do not grow due to the insufficient light. However, the number of invasive plant species is growing in proportion while the coverage of native plant species trees is decreasing. The rise of the level of illumination increases not only the number of individuals in the populations, but also the above-ground biomass of I. parviflora: plants are larger, produce more side shoots. According to a study conducted by Richardson et al. (2012), under the stressful environment the negative effect of the invasive plants are reduced, whereas the successful negative effect of the invasive plants on the invaded ecosystem improved with increase in nutrient levels.

Impact of Invasive Species on Native Ecosystems

The background research of native and non-native surrounding plant competition was studied because the University of Wollongong (UOW) campus has a native dominated array of plant species. The reasons that lead to our hypothesis were the artificial planting, and maintenance of the UOW campus and high human interaction the plant competition

Research Aims: 

Assess the impact health of the competition type with non-native and native species

To assess if more non-native species surround the target species the health of the plant will be stunted

General Objective 

To determine the effect of native vs. non-native surrounding plant competition on Grevilleas and Linospadix monostachya

Specific Objective 

1. To determine the flowering bud/fruits abundance when the Grevilleasand Linospadix monostachya species are surrounded mostly by non-native species.
2. To determine the effect of non-native surrounding species on the height of the Grevilleasand Linospadix monostachya
3. To assess the effect of more surrounding native species on the leaf growth of the Grevilleasand Linospadix monostachya

Hypotheses:

1. There would be a lower abundance of flowering buds/fruit when the target species are surrounded by mostly non-natives species
2. The non-native species surrounding will influence the height of the targeted species
3. The more native species surrounding will limit the leaf growth of the targeted species

Factors Associated with Invasive plant species transitioning from Casual, to Naturalized, to Invasive

According to Richardson et al. (2012), the invasive plant species undergo different stages before fully becoming an invasive species in a new ecosystem: introduction of invasive species propagules, presence as casual strange plant species, naturalization and dispersal. The invasive plant species overcomes certain barriers during transition from one stage to another. A study conducted by (Adamowski et al. 2008; Davies et al. 2010; Li et al. 2015), established the barriers to include a combination of abiotic and biotic. However, the two studies recommended further studies on prediction of future invasion and elucidation of more factors that helps the invasive species in overcoming the barriers. At the same time, according to (Milbau and Stout 2008), the naturalization and invasiveness of an alien plant species in a new environment depends on various parameters that are related to the invasion history, native distribution, biological, and ecological characteristics. Li et al. (2015), concluded that some of the critical parameters associated with naturalization of an invasive plant species include clonal growth, high moisture, and low nitrogen. A study by Leishman and Thomson (2005), supports the argument that the predictors of probability of naturalization and subsequent plant invasive is largely dependent on the invasion history, the native range, and the ecology of the alien plant species as earlier suggested. Studies have established that the factors contributing to most probability of being invasive such as ornamental introduction, hermaphrodite flowers, and mode of pollination does not directly impact the processes of invasive plant species naturalization (Skálová et al. 2013; Pyšek and Richardson 2010). In fact, for naturalization of alien species clonal growth and nitrogen indicator score are cited as the most import factors as suggested by (Pyšek and Richardson, 2008; Milbau and Stout, 2008).

Barriers to Naturalization and Invasion of Non-Native Species

Species coexistence and possible implications for future invasion dynamics

Argument about the relationship between invasive plant species and native species has been around for decades. In fact some research findings reveals a positive coexistence (Hui et al. 2016; Lonsdale 1999; Meiners et al. 2004), whereas other studies have presented a negative relationship (Knops et al. 1999; Kennedy et al. 2002). Evidence from various studies have revealed that logging, thinning of tree stands, and soil disturbance is real catalyst for forest interiors invasion by the alien plant species (Li et al. 2015; Dawson et al. 2015; Brothers and Spingarn 1992). The deliberate cultivation of the forest by the forest management team promotes invasion of the forest according to (Zhai et al. 2018; Watkins et al. 2001).

Different studies have suggested long-term coexistence between invasive pant species and native species in the same locality under different microsite requirement (Skálová et al. 2013; Cadotte and Lovett 2001). However, according to ?uda et al. (2015), the ecological conditions under which two or three species coexist is limited. For example, post-invasion characteristic divergence leading to increased size, early germination, improved phenotypic plasticity were identified as main facilitating traits for the co-existence between I. noli-tangere with I. parvi?ora (Clements et al. 2008).

According to Dayan and Simberloff (2005), in the presence of native congener, as strong competition from the invading alien plant species is highly expected. At the same time, different environmental factors may give invasive plant species a competitive edge over native plants species. Stressful environmental conditions is associated with reduced negative effect of invasive plant species on the native plant in the same ecosystem (Richardson et al. 2012).

Leaf trait relationships of native and invasive plants

The leaf trait variation is a strategy in plant ecology, it involves carbon fixation strategy as suggested by (Westoby et al. 2002; Wright et al. 2004). According to Leishman (2007), plant species with low speci?c leaf area (SLA) usually have longer leaf life span (LL) as compared to the plant species with high specific leaf area, suggesting that longer LL requires greater structural strength. A study conducted by McAlpine et al. (2017), concluded that SLA promotes plant species invasiveness this findings was consistence with the findings from a research conducted by (Leishman et al. 2010). According to (McAlpine et al. 2017), the alien invasive species have hairy leaves and higher specific leaf area compared to alien non-invasive and native species. Moreover, the invasive species in disturbed sites are known to have smaller seeds and flowers longer as compared to native; the alien invasive species more dispersed by wind and vertebrates and less by ants; and invasive species are more propagated as compared to native plant species. A study conducted to correlate abundance at both scales, SLA registered a continental scale hence supporting the argument that leaf size is major contributor the success of the invasive species (Cadotte et al. 2006).Invasive species are best known to exploit vegetative propagation, have larger leaves and they flower for a longer period in summer contrary to non-invasive species (Pyšek and Jarošík 2005). There is clear difference between native and invasive exotic plant species based on their leaf traits (Leishman et al. 2010), In fact, there was established leaf trait scaling relationships found between  the groups both within the community and across range of species.

Relationship Between Native and Non-Native Species

Study setting 

The background research of native and non-native surrounding plant competition was studied because the University of Wollongong (UOW) campus has a native dominated array of plant species.

Sample population 

Phenotypic parameters such as plant leaf length, number of fruits/flowers, and plant height of the target species were registered. For each species 15 samples were taken as follows 5 surrounded by primarily natives; 5 surrounded by primarily non-natives; surrounded by both

Study design and Sampling procedure

The Artificial and primarily native plants species were randomly analyzed from all over the UOW campus, some other observations that were made were changes in soil colour and percentage of canopy shading; however these were not noted down.

Variables

• Independent: Proportion of native/non-native plants surrounding
• Dependent: Tree height, number of flowers/fruit, average leaf length

Treatment and replications

For each species sampling was carried our as follows: 5 surrounded by primarily natives; 5surrounded by primarily non-natives; 5 surrounded by both. Only trees with a minimum of 2m height were sampled.10 living leaves were sampled from each species. All flower/fruit including evidence of flowering/fruiting.

Data collection

The height of the tree was measured using tape measure and the readings recorded. The number of native and non-native plant species within 2 meters radius surrounding the selected tree were identified and counted. All the flowers and fruits on the selected target plant species were counted. 10 live leaves were identified and their length measured.

Data Analysis 

A single factor ANOVA was used to compare whether there was mean number difference in abundance of flowering buds/fruit when Grevilleas and Linospadix monostachya specie are surrounded by mostly native and non-natives species. Sharpio Wilks test was used to test for the normality distribution of the flower data collected from the target species. This was to ensure that the data from each group was normally distributed. Tukeys test was used to analyses for unequal observations in the mean (±SE) length (cm) of leaves on Linospadix monostachyos surrounded by mostly natives, non-native. Therefore, we were able to clarify between the two target species which one specifically have mean significance difference

Patterns in results

Argument about the coexistence between invasive plant species and native species has been around for decades. In fact some research findings reveals a positive coexistence (Hui et al.2016; Lonsdale 1999; Meiners et al. 2004), whereas other studies have presented a negative relationship (Knops et al. 1999; Kennedy et al. 2002). However, we found no competition effect from mostly native and non-native on the flowering/fruit on Grevilleas or Linospadix monostachyos. This findings are in line with findings from a study conducted by (?uda et al. 2015). Moreover, Grevilleas prefer non-native competition, particularly when compared to the 50-50 distribution of native and non-native competition. The Walking Stick Palm favored the even distribution of 50% native and 50% non-native plant competition above other competition scenarios. Walking stick palm performed well having registered higher mean number of fruits when surrounded by mostly non-native plant species. This corresponds to the findings by (Dayan and Simberloff 2005), who concluded that in the presence of native congener, as strong competition from the invading alien plant species is highly expected. We could attribute our findings to environmental factors that could have given Linospadix monostachyos a competitive edge over non-native plants species, with regards to number of fruits recorded. According to Richardson et al. (2012), Stressful environmental conditions is associated with reduced negative effect of invasive plant species on the native plant in the same ecosystem. Thus, the environmental factors may be more influential upon the health (growth and flowering) of Grevillea and Walking Stick Palm compared to the competitors in the ecosystem.

Effect of Surrounding Plant Competition on Plant Health

The results from our study showered that Grevilleas when surrounded by mostly non-natives had a higher average height. Therefore, it is evident from the result that Grevilleas was a strong competitor when surrounded by mostly non-native plant species. Our research findings are concurrent with study findings by (Skálová et al. 2012), whose findings revealed that most competitive invasive plant species were taller. The tall stature of Grevilleas species gives it considerable advantage of light absorption and utilization for photosynthesis. Whereas, walking stick palms when surrounded by mostly non-natives had a lower average height, we found a negative relationship between walking stick palms and non-native species. Though not statistically significant. Our findings contradicts the findings from studies conducted by (Alpert et al. 2000; Goodwin et al. 1999). Our research findings could be supported by the fact that the species were artificially plated on the UOW campus. Therefore, the plants ability to ward off potential invasion success against native or non-native competition was compromised.

From our study findings competition type had a significant effect on the average leaf length on Linospadix monostachyos but not on Grevilleas species, but not statistically difference (p=0.0767). Therefore, Grevilleas species coexisted well with the competitors. Our study findings is supported by other studies that suggested long-term coexistence between invasive pant species and native species in the same locality under different microsite requirement (Skálová et al. 2013; Cadotte and Lovett 2001; Lloret et al. 2005). However, according to ?uda et al. (2015), the ecological conditions under which two or three species coexist is limited. Linospadix monostachyos response based on the leaf length makes it more susceptible to competition from native and non-native invasive plant species. This was supported by findings from a study conducted by (Lloret et al. 2004), whose research findings revealed that aliens with large leaves are more likely to become abundant in number. For example, post-invasion characteristic divergence leading to increased size, early germination, improved phenotypic plasticity were identified as main facilitating traits for the co-existence between I. noli-tangere with I. parvi?ora (Clements et al. 2008). Our findings is further supported by other studies that have suggested that there exists an association between large plant leaf size and it ability to compete well in the ecosystem (Lloret et al. 2005; Leishman et al. 2010). Consequently, the findings from our study results substantiate the hypothesis that invasion success by the alien plant species is attributed to the functional characteristics qualitatively different from those happening in the native flora, whereby some life-forms may be more saturated as compared to others as suggested by (Crawley et al. 1996).

Discussion – other observations

As the plants were randomly analyzed from all over the UOW campus, some other observations that were made were changes in soil colour and percentage of canopy shading; however these were not noted down.

Study Limitation 

In the process of doing our research some of the limitations we encountered include the difficulty in identifying native plant from non-native plant and data analysis.

Conclusion

Inclusion the competition type had no significant effect on the number of flowers/fruit on Grevilleas or Linospadix monostachyos. At the same time, from our study findings we can conclude that non-native plant species has impact on ecosystem.

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