Native vs Exotic Plants & Pollinators in Urban Green Space

Summary

This report is to identify the native versus exotic plant species that have visited by the most insect pollinators in the urban greenspace by the monitoring program which is conducted by the citizen scientists and discuss the management strategies that can enhance the pollinator diversity with the help from people in the world. Pollinators is suggested to be the success of all restoration efforts that is critical to the perpetuation of the plant species. The native insect pollinators are suggested to be more likely attracted by the native plants due to the native-native interactions are more common in the urban greenspace. However, due to the land-use, climate change and invasive alien species which also the factors that caused the interaction between native pollinators and exotic plant species become a common interaction that is parallel to the native-native interaction. The study of this monitoring program will help us to learn about the management strategies that protect and enhance pollinator diversity with the help of human which can increase the relationship between human and nature.

Introduction

Increasing evidence that pollinators and the plants they pollinate are negatively affected by environmental change. These pressure include climate change, diseases, pests and pathogens and invasive species (Vanbergen et al., 2018). Management strategies therefore need to focus not just on current issues but consider the response and resilience of these systems to future environmental shocks (Senapathi et al., 2015). Generalist pollinator species such as flies, bees and wasps are connected to a large range of other species. If the composition of the surrounding environment decreases, this will impact the diversity of pollinators and pollination. Decrease of plant species that produce the pollen and nectar resources, has been identified as the main driver for diversity decrease of the pollinator species and suggesting that more emphasis on providing foraging and nesting habitat resources for the pollinator species might protecting and enhancing the pollinator biodiversity (Senapathi et al., 2015). Low response diversity will cause the “whole functional groups to go extinct or make systems ecologically insignificant as a result of environmental change” (Senapathi et al., 2015). However, greater diversity of species will cause “functional redundancy where several species can contribute in a similar way to ecosystem function and loss of some dominant species can be ameliorated by the presence of other rare species” (Senapathi et al., 2015). Hence, it is important to keep the diversity of pollinator species in a balance condition. Native pollinators are extremely important because they maintain productive, diverse plant communities and help pollinate many of our agricultural crops.

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This aim of this report is to identify the native versus exotic plant species that have visited by the most insect pollinators in the urban greenspace and discuss the management strategies that can protect and enhance the pollinator diversity with the help from people around the world.

Methods

Survey was conducted to identify the native versus exotic plant species that have visited by the most insect pollinators in the urban greenspace. 10 of the Australian native species of plants and insects and 10 of the exotic species of plants and insects were selected to be included in the survey. The resulting data were analyzed to determine the most common interactions and the impacts to the pollinator density. The study was conducted in the Melbourne Garden, Royal Botanical Garden Victoria. We selected 10 different sites according to 10 different species as each site is defined by a species of native or exotic flowering plants. The research was conducted between 1/9/2019 - 6/10/2019 in a day which have good weather. 68 applied ecology students of University of Melbourne who have underwent training on identifying native and exotic pollinator species. 10 observatories were chosen in the Royal Botanic Garden Victoria. Surveys was conducted using a measure window of a threshold of >2500mm2, ruler, recording sheet and a pen. At each observatory, observer would take down 3 set of the size of the flower in x and y within the measure window, the total number of flowers in the measure window and the area of the measure window. After that, the observers were required to do a 7 minutes of the observation on the measure plants of recording the presence and the absence of the pollinators landing on an open flower.

Considering the observations, p-value = 0.0002445 which is less than 0.5 consider a statically significant with the mean of 0.18328681 for the native flowerosity and mean of 0.08601541 for the exotic flowerosity. Which means that the distributions of native flowerosity is more than the exotic flowerosity. According to Ebeling, Klein, Schumacher, Weisser & Tscharntke (2008), the number of flowerosity will enhanced the pollinator insect species density. According from the result that we get, it shows that the number of flowerosity does not affect the number of pollinators species visit a plant. This may be caused by the climate change that affects these mutualistic interactions between the plants and pollinators. Climate change such as increases of rainfall will decrease the activity of the pollination by affect the floral resource availability and quality for pollinating insects and the patterns of pollen flow and pollination success for plants (Scaven & Rafferty, 2013). It also will affect the pollen degradation and nectar dilution (Lawson & Rands, 2019).

Plant-pollinator interactions

The differences in observed interactions among native versus exotic insects among native plants with the ratio of 3.410256 and the p-value of 0.00000000000000022 (p < 0.5) is statically significant. On the other hand, the differences in observed interactions among native versus exotic insects among exotic plants with the ratio of 1.572464 and p-value of 0.00003242 which is less statically significant than the differences of the interactions among pollinators and plants of native-native and exotic-native.

According to Figure 1, the plant-pollinator interactions of native-native are the most common interaction (38% of the visitations) and the exotic-native is the second most common interaction (31% of the visitations). There are no significant evidences that can support that exotic plants have negative or positive impact on the native pollinators (Stout & Tiedeken, 2017). This is the reason why exotic plants attracted native pollinators which is about the same as the native-native interactions. The reason why native-native interactions are the most common is because exotic plants may not provide enough nectar or pollen to the pollinators (Reel & Seiler, 2010).

Discussion

Pollinators provide numerous benefits including maintenance of biodiversity and the ecosystem stability (Potts et.al, 2016). However, pollinators are decreasing nowadays as they are facing multiple threats such as changes in land-use, climate change and invasive alien species. Land-use intensification primarily triggers losses in flower diversity, which could lead to nonrandom and resource mediated declines in certain pollinators (Weiner et al., 2014). The increases of temperature will reduce the floral resources (pollen and nectar) available for 17% - 50% of the pollinator species (Kjøhl, Nielsen & Stenseth, 2011). Invasive alien species pollen and nectar in pollinator diets may produce risks for pollinator health (Vanbergen et al., 2018). To maintain the diversity of pollinators or even increase the diversity of pollinators in the urban green space, here are some recommendations for the urban green space management to the City of Melbourne:

Plant native wildflowers

Native Wildflowers bloom at different times of the year which can provide food resources such as pollen and nectar to the pollinators throughout the year (Campbell, 2014). Many species of wildflowers are easy to grow and their variety of shapes and colors attract a multitude of different pollinators. This can ensure that the pollinators will not suffer from the pollen and nectar throughout the year. Native wildflowers are especially adapted to the climate, soil and conditions of a country, and suit the indigenous wildlife, without upsetting the balance of nature (Australia's native vegetation framework, 2012). Wildflower plantings have been demonstrated as an effective practice for benefiting pollination (Feltham et al., 2015). This can be easily done by organizing a plant native wildflowers event which allow all the citizen in town to participate and get to know how pollinators affect the environment and how native plants help to enhance the diversity of the pollinators.

Provide nesting habitats

In order for the pollinators to survive and thrive, safe nesting habitats are required to provide the pollinators with shelter for protecting them from predators and allow pollinators to grow and develop by themselves (National Biodiversity Data Centre Series, 2016). All agroforestry plantings can provide excellent nesting opportunities for the pollinators (Agroforestry notes, 1996). Hollow bamboo sticks, drilled and untreated wood blocks, organic debris on the ground and dead vegetation or wood are the habitat for many beneficial native bees, wasps, flies and other pollinators (Campbell, 2014). By setting up this nesting habitat allow the pollinators to maintain and establish new nesting sites and remember, do not till the soil as this will disturb the habitat of the pollinators. Techniques for protecting and enhancing the pollinators nesting habitats will help to increase the diversity and abundance of the pollinators (Mace & Scott, 2008). With the help of citizen by just walking on the path that are provided in the park instead of stepping out of the path will definitely decrease the disturbance of the pollinators habitats. The management staff should have poster or sign that remind people of this act around the urban green space. So that all the citizens are participate in maintaining and increasing the diversity of pollinators to maintenance of biodiversity and the ecosystem stability.

Use pesticides wisely

Minimizing use of herbicides and pesticides is also essential to ensuring pollinators survival (Mace & Scott, 2008). Good nursery practices together with best management practices for herbicide and pesticide use can help to reduce the unwanted side effects of pesticides and provide a refuge for native pollinators (Mace & Scott, 2008). Whenever feasible, consider non-pesticide solutions first. If the pest level has reached an economic threshold and pesticides must be used, best management practices can help minimize their risk to pollinators (Mace & Scott, 2008). When pesticides are used, application should occur during early morning, late afternoon, or at night, when pollinator activity is low because this can limit the pesticide use that have impacts of the pollinators (Mace & Scott, 2008).

The diverse community of pollinators will increase by providing pollen and nectar sources, nesting sites and protection from pesticides (Mace & Scott, 2008). With the solution of increasing the diversity of native flower species which will help to provide pollen and nectar sources that have no risks to the pollinators. Moreover, providing nesting habitats as the shelters to the pollinators will help to protect the pollinators from the predators and also climate change. The another solution is to have protection from pesticides since pesticides have negative impacts to the pollinators by minimizing the use of pesticides to ensure the survival of the pollinators.

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