Essay on Exotic Vs Invasive Species

Lantana camara is an exotic weed that is distributed throughout the tropical and subtropical world regions (Holm et al 1997) it originated from Central and South America and was introduced into the Philippines from Hawaii and became naturalized. It was introduced as an ornamental plant for gardening because of its colorful flowers of different hybrids (pink, orange, and yellow) and it thrives well because of its tolerance to a wide array of environmental conditions and habitats with allelopathic chemicals in all its parts. It has efficient advantages over native species under conditions of light, soil moisture, and nutrients making it an efficient competitor. studies claim that the distribution of Lantana camara will likely expand in the future with projections most particularly to habitats where it has become established with suitable climatic conditions (Vardien et al 2012). Effective suppression of its proliferation is by preventing seed dispersal which will consequently inhibit both seed germination as well as seedling establishment resulting in declined productivity of the invasive weed.

In general, there are three known options for the control of an invasive species: chemical control, physical control, and biological control. Each of these has its pros and cons. No definite effective control measure has yet been found. Integrating all control options, the physical, mechanical, and biocontrol options depending on the scale of the weed infestation and to which control method can be feasible is suggested and will likely result in improved control and mitigation strategies. In addition, principles underpinning strategic control need collective action at all levels of governments, NGOs, and communities. Promoting community awareness about the negative impacts of Lantana’s invasion would optimize control success.

Introduction

Invasive Alien Species also known as exotic species are plant and animal species that are introduced to areas outside their natural geographic range wherein, they are not native or present by nature. Their introduction may be accidental or by purpose and consequently poses adverse ecological and economic impacts (Bruton and Meron 1985; De Silva 1989). As introduced to their non-native area, invasive species outcompete the existing native species in the area where they don’t have existing natural predators and proliferate. Another factor that contributes to their proliferation is the ecological suitability of the new habitat. Competition for resources, predation, niche displacement, hybridization, introgression and extinction (Mooney and Cleland 2001) are consequences faced by native species with their encounter with invasive species. Organism transport to a new habitat either between islands and countries, establishment and growth of the species the natural or man-made habitats, and the spread of the species to large areas at an uncontrolled rate are the introduction pathways of the exotic species. In the Philippines, some exotic species are for the production of food supply, reforestation projects, and horticulture. Today, people still lack awareness of the negative impacts of invasive species, and efforts to create invasive species awareness are needed.

This paper particularly highlights the species Lantana camara, an exotic weed that is distributed throughout the tropical and subtropical world regions (Holm et al 1997), originated from Central and South America and was introduced into the Philippines from Hawaii and became naturalized. It was introduced as an ornamental plant for gardening because of its colorful flowers of different hybrids (pink, orange, and yellow) and it thrives well because of its tolerance to heat. The species is considered one of the most invasive plant species in the Philippines (ISSG, 2006) as it invades both natural and agricultural ecosystems and reduces productivity. It has varied impacts ranging from ecological processes, and adverse effects to native plant diversity, and native disturbance regime alterations. Their impact on vegetation affects herbivores and carnivores that feed on them thereby threatening livestock. Lantana alters species composition of understory species and tree seedlings, and also it covers grass, understory vegetation, and tree seedlings free of herbivory, in turn increasing the lantana density beneath thickets – which will become denser when simply slashed or uprooted making it hard to eradicate (ECZ, 2004). The lantana can last in seed banks for several years then invade and eventually dominate forest understory. In addition, the plant is known to spread and infest rapidly with resistance to cutting and burning. In particular, it colonizes the gaps and edges of disturbed forests or logged habitats. The plant is also abundant and distributed in grass habitats due to the absence of shading effects and frequent former land use disturbances plant narrowed the size of farmlands and created difficulties in the cultivation of crops. The prickly impenetrable thickets of lantana, not only completely hinder the movement of animals, and prevent them from searching for food, but also puncture their skins and cause injury (Alemu and Terefe 2015). The weed is prone to the spread of fire and may consequently alter the fire regime in favor of its persistence (Hiremath & Sundaram 2005). The fire then causes the mortality of neighboring seeds and seedling mortality of other species in the area (Moore & Wein 1977). Inhibiting both seed germination as well as seedling establishment, resulting in declined productivity. Thus, this invasive weed species cover may create demographic instability among tree species consequently reducing tree diversity and changing forest structures in the future (Sharma 2010). Lantana populations were growing across all land uses. Its historical demography showed that weather (from El Nino to La Nina) had a strong influence on its demography having a strong positive effect on the population growth rate. In addition, Lantana camara inhibits the growth of species near it due to its allelopathic effects present in all its parts interfering with the germination of many species (Ambika 2003, Bais 2004, and Kumar 2011) of crops, weeds, bryophytes, and vegetables (Mishra, 2015). It is known to have efficient advantages over native species under conditions of light, soil moisture, and nutrients making it an efficient competitor. Allelopathy caused by lantana reduces early growth rates hence increasing mortality to other plant species (Sharma et al. 2005a, 2005b), resulting in overall decreased species diversity and cover (Gentle & Duggin 1998; Loyn & French 1991). Most studies claim that the distribution of Lantana camara will likely expand in the future with projections most particularly to habitats where it has become established with suitable climatic conditions (Vardien et al 2012). From this, we can derive strategic planning by biosecurity agencies, identifying areas to target for eradication or containment. Distribution maps of the risk of potential invasion can be useful tools in public awareness campaigns and effective responses be taken.

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In general, there are three means of exotic species removal and it can done via mechanical, chemical, or biological control all of which can be applied to an integrated invasive species management plan (Williams and West, 2000). Mechanical or physical controls (like bulldozing and plowing) are effective and are suitable for moderate infestations. Thinning and pruning methods of control were also frequently used. However, eradication of a weed that has become established is costly (Bhagwat et al., 2012; McConnachie et al., 2012) and difficult (Baars & Heystek, 2003). As mentioned, lantana is difficult to eradicate because it will coppice and form thickets if simply removed via uprooting or slashing. The study of Toland et al, 2005 showed a significant relationship between forest gap in canopy and lantana pollinator visitation consequently facilitating the invasion of lantana and recommended a program for selective physical removal of L. camara individuals and that sprouting of its shoots should be removed continuously, such that flowering is prevented in the process. The secondary spread of L. camara will then be hindered by gaps in forest interiors.

Even with the widespread distribution of lantana, the costs of chemical and mechanical control, and its invasion of both agricultural and natural lands, its current management is mainly focused on the use of specialist insects and pathogens in efforts to find effective biocontrol of this weed (Day et al. 2003). The use of such biological control was claimed to be proven as a potentially cost-effective, and safe method for the management of invasive weeds. However, the host specificity, altitude, and seasonal preferences of released agents, the number of agents introduced, and the extent of the invaded area likely limit the success of biological control (Zalucki et al., 2007). Furthermore, no standard methods have been formulated for effective management of the species and it may be because of its occurrence in such a wide array of land uses and vegetation, where perceptions of the species, management goals, and resources present differ considerably. Suites of methods are often used, the particulars of which are dependent on the land use, extent and density of the invasive populations, accessibility to invaded areas, economic value of land, and the associated costs (Day et al, 2003). For an effective biological control agent, it may need to strongly limit the growth of juveniles into the adult stages, especially in sites where lantana is free from competition, like in fire and grazing, and they need to implement this specifically during wet years (Rhagu et al, 2014). Management of land use practices particularly as fire and grazing pressure should be noted regarding this. (Osunkoya, Perrett, Fernando, Clark, & Raghu2013).

Mitigation Framework

Presented below is a diagram showing the different control methods of the weed and each of its pros and cons. Each control method option has its pros and cons. Chemical control like the usage of herbicides is effective and yields definite damage to the invasive weed, nonlabor intensive and easy application yet the method is costly and may pose risks to human health and further cause environmental degradation. The physical or mechanical control is effective and suitable to levels of medium-sized infestations only and is not feasible for large-scale infestations for it will be costly and labor intensive. Lastly, biological control is the natural and safer control option that is efficient and applicable to large-scale invasions. On the downside, introduced biological agents are not fully successful due to host specificity because of the lantana hybridization and no phytophagous agents have been introduced yet. Also, agents have differing altitude and seasonal preferences, so they vary across habitats land use types, and climate regimes. Research on effective biocontrol agents is still ongoing.

To sum it all up, coming up with a long-term and sustainable control of the invasive lantana weed is suggested that the benefits and adverse impacts should be resolved through proper management options integrating the physical mechanical, and biocontrol options depending on the scale of the weed infestation and to which control method can be feasible. Secondly, the principles underpinning strategic control need collective action at all levels of governments, NGOs, and communities. Promoting community awareness about the negative impacts of Lantana’s invasion would optimize control success. Moreover, integration of such techniques will likely result in improved control and mitigation strategies.

References

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