Master of Science

Growing halophytes using saline water would be a feasible solution to the declining availability of fresh water. On aeroponically grown edible halophytes Mesembryanthemum crystallinum and Portulaca oleracea, this study investigated 1) the impacts that different percentage of artificial seawater (ASW) had on the plant growth, water relations, photosynthetic performance and nutritional quality; 2) the interactive effects of ASW and light spectrum quality on growth, water relations, photosynthetic performances and nutritional quality; and 3) the effects of salt priming under effective LED lighting on growth and nutritional quality. Both M. crystallinum and P. oleracea grew under LED of R/B 2.2 in 10%, 20%, 30%, 40%, 60%, 80% and 100% ASW for the first objective. Shoot and root biomass generally decreased with increasing saline concentration for both plants. However, M. crystallinum exhibited a high level of salt tolerance and grew well in 100% ASW while P. oleracea were not able to survive in 100% ASW. It was found that 10% ASW was the most favorable condition tested for the growth of both plants. When severely salt stressed at 60% ASW, both plants induced CAM photosynthesis to manage its water status. The findings of this study suggest that M. crystallinum had a higher salt tolerance, and possibly equipped with more robust mechanisms to alleviate the oxidative stress, than P. oleracea. As for the second objective, both plants were grown under R/B LED ratio of 0.9 and 2.2 in 10% and 40% ASW. M. crystallinum grown in 10% ASW under R/B 2.2. and P. oleracea grown in 10% ASW under R/B 0.9 had higher productivities. This had once again proven that low salinity favours photoassimilate accumulation. Both plants relied heavily on proline to counter oxidative stress at higher salinity concentration of 40% ASW under both light conditions. There were no clear correlation between antioxidant enzymes and dietary minerals studied with salinity treatment and light conditions as they could possibly be dependent on species and other environmental conditions. Large amount of Na+ was found in both plants grown in 40% ASW regardless of light conditions. Ultimately, for the third objective, the plants were grown under R/B LED ratio of 2.2. The seedlings were grown in 10% ASW for 10 days (I) after transplant where the first harvest occur. From day 11 to 16 of transplant, both types of plants were exposed to 4 different treatments before harvesting on day 16, i.e. II: 10% ASW; III: 80% ASW; IV: 40% ASW ⟹ 80% ASW; V: 40% ASW ⟹ 60% ASW ⟹ 80% ASW. Primed M. crystallinum had higher productivities than those that were not primed. However, priming had not much effect on the productivities on P. oleracea. Priming resulted in enhanced proline accumulation, Asc concentration, soluble sugars and antioxidant enzymes activities in M. crystallinum. However, it did not have much effect on proline accumulation and antioxidant enzyme activities in P. oleracea. A reduction of Na+ was observed both plants when primed, and once again, no distinct trends were observed between dietary minerals and salt priming.

It is important to have a good understanding of the habitat selection patterns of the fauna inhabiting a landscape, as it helps to guide wildlife management, conservation, and monitoring efforts. However, basic ecological knowledge of the distribution and micro-habitat preferences are lacking for many terrestrial mammals, despite the crucial role they play in maintaining ecosystem stability and function. Through camera-trap surveys, this study aims to investigate the habitat selection patterns of terrestrial mammals within the Central Catchment Area in Singapore by correlating their spatial distribution with the heterogenous environment they inhabit.

To assist in the processing of the camera-trap images obtained, a convolutional neural network model was built to classify each image as either empty, containing a human, or containing an animal. The convolutional neural network model was trained using camera-trap images captured at various nature areas and habitats across Singapore to ensure accuracy of the model to Singapore’s landscape. The trained model was found to be effective in classifying camera-trap images, with an F1 score of 89.6% for the images captured at Central Catchment Nature Reserve. It also enabled 85.9% of the images at Central Catchment Nature Reserve to be filtered out of the manual identification process, saving significant manpower and time required for image processing.

Single-season, single-species occupancy modelling was conducted using distance to trail, distance to edge, light detecting and ranging (LiDAR) scan point densities of the understorey vegetation, Normalised Difference Vegetation Index, and Inverted Red Edge Chlorophyll Index as environmental covariates. Occupancy modelling was conducted for the terrestrial mammals recorded on the camera traps set up within the Central Catchment Area. Both the effect direction and relative importance of each covariate was determined for each species, and model-averaged estimates of habitat use and detection probability were also calculated from the selected models.

None of the environmental factors were found to be significant for all of the terrestrial mammals tested; instead, each species had a unique combination of environmental factors influencing its habitat selection patterns. Each environmental covariate was also found to have different effect directions and relative importance across the different species, showing that habitat selection patterns are unique to each species and should not be generalised across species groups. Comparing these results to another habitat selection study also conducted within the Central Catchment Area, habitat selection patterns of the lesser mousedeer, sambar deer, and wild boar were similar, except for the effect of understorey density, whereby it was found that understorey density was actually a significant environmental factor influencing the habitat selection patterns of the three abovementioned species.

Estimated habitat use of each species across the entire Central Catchment Area suggests that the long-tailed macaque and wild boar use most of the available landscape (99.9% and 98.9%, respectively), compared to the other non-generalist species. Knowledge of such land use is important for wildlife managers, considering that these two species are conflict species in Singapore. Unfortunately, LiDAR data across the entire study site are currently unavailable, and this limits the identification of specific areas that are used for each species.

The thesis is about the study of a new approach of de ning the quasicontinuous dcpos that was rst proposed by Heckmann and Keimel in their paper [8]. This method relies on de ning the quasicontinuous dcpos X as those whose Smyth powerdomain Q(X), i.e., the corresponding dcpos of nitely generated compact saturated subsets of X ordered by reverse inclusion (i.e., the Smyth-order v), are continuous domains. Such an approach facilitated many simpler proofs for the elementary results concerning quasicontinuous dcpos as well as the upper powerspace, endowed with the upper Vietoris topology.

My undergraduate experience allowed me a rst taste of using topology in a special topic in number theory, i.e., Furstenberg's Proof of the In nitude of Primes. My interest in topology started since then, and I wanted to explore deeper into topology. Given my very meagre topological experience, I had to amass a huge volume of background knowledge in topology, particularly in non-Hausdorff topology, before I could even begin to embark on my journey to study Domain Theory. To say the least, the learning curve for me in acquiring this body of mathematical knowledge is very steep for me.

Part of this thesis is devoted to building this background knowledge, which comprises of three components: (i) Topology, (ii) Order theory which is about studying ordered structures like posets, lattices, complete lattices, dcpos, etc., and (iii) the theory of continuous domains.