Spatiotemporal Dynamics Induced by Nonlocal Competition in a Diffusion Predator-Prey System with Habitat Complexity

In this paper, we study a delayed diffusive predator-prey model with nonlocal competition in prey and habitat complexity. The local stability of coexisting equilibrium are studied by analyzing the eigenvalue spectrum. Time delay inducing Hopf bifurcation is investigated by using time delay as bifurcation parameter. We give some conditions for determining the bifurcation direction and the stability of the bifurcating periodic solution by utilizing the normal form method and center manifold theorem. Our results suggest that only nonlocal competition and diffusion together can induce stably spatial inhomogeneous bifurcating periodic solutions.

From Coastal to Montane Forest Ecosystems, Using Drones for Multi-Species Research in the Tropics

Biodiversity monitoring is crucial in tackling defaunation in the Anthropocene, particularly in tropical ecosystems. However, field surveys are often limited by habitat complexity, logistical constraints, financing and detectability. Hence, leveraging drones technology for species monitoring is required to overcome the caveats of conventional surveys. We investigated prospective methods for wildlife monitoring using drones in four ecosystems. We surveyed waterbird populations in Pulau Rambut, a community of ungulates in Baluran and endemic non-human primates in Gunung Halimun-Salak, Indonesia in 2021 using a DJI Matrice 300 RTK and DJI Mavic 2 Enterprise Dual with additional thermal sensors. We then, consecutively, implemented two survey methods at three sites to compare the efficacy of drones against traditional ground survey methods for each species. The results show that drone surveys provide advantages over ground surveys, including precise size estimation, less disturbance and broader area coverage. Moreover, heat signatures helped to detect species which were not easily spotted in the radiometric imagery, while the detailed radiometric imagery allowed for species identification. Our research also demonstrates that machine learning approaches show a relatively high performance in species detection. Our approaches prove promising for wildlife surveys using drones in different ecosystems in tropical forests.

The Effect of Habitat Structural Complexity on Gastropods in Anarid Mangrove Wetland

Structural complexity of mangrove forests are thought to provide critical habitats for a variety of invertebrates. We studied the influence of mangrove structure and seasonality on the gastropod diversity in the extreme mangrove ecosystem of the Persian Gulf. Sampling was conducted in two successive years (February and June 2018, February and June 2019) at two mangrove habitats i.e., pneumatophore zone and mudflats. The communities were characterized by the dominance of specific taxa and the comparably low species richness. In total, 18 taxa were identified, including 14 species occurring in the mangrove forest and 16 species in the mudflats. Assimineidae dominated the community in both mangrove habitats. Mean density of gastropods was 1.5-fold higher in the pneumatophore zone (86.12±135.21 ind.m-2) than in the mudflats (54.33±108.69 ind.m-2). Species such as Haminoea vitrea, Peronia verruculata, Assiminea mesopotamica and Platevindex tigrinus were found to benefit from the presence of pneumatophores, which highlights the importance of local habitat complexity. Gastropod communities varied significantly between the habitats, but there was little difference in the community structure between seasons. Distance-based linear models revealed that total organic carbon and total organic nitrogen best explained the variation in gastropods community structure.

The consequences of complex habitat loss for the New Zealand blue cod, Parapercis colias

<p>Climate driven threats are predicted to decrease the complexity of biogenic habitats. Within temperate coastal marine environments, we know that complex macroalgal beds support more complex communities through the provision of microhabitats and refuges. Macroalgal habitats have potential interacting benefits and costs for predators, as increased macroalgal biomass supports higher richness and diversity of prey species, but prey within these habitats might be more difficult to catch. An important New Zealand fishery species, the blue cod (Parapercis colias), is a large bodied temperate reef fish found exclusively throughout the coastal waters of New Zealand. Its dependence on subtidal coastal reef environments mean that it is important to understand how a loss of complex macroalgal habitats might alter the way that blue cod forage, and how the trade-off between prey abundance and availability will affect its abundance and productivity. This thesis aims to understand the influence of complex macroalgal habitats on P. colias prey availability and behaviour, on the foraging success of P. colias, and ultimately on P. colias population dynamics. Experiments were conducted using choice chambers to evaluate whether two alternate P. colias prey, Forsterygion lapillum and Heterozius rotundifrons, showed a preference for complex habitats with and without predation risk. Both species preferred complex habitats in the absence of predation cues, but F. lapillum showed a more consistent preference for complexity in response to predation risk. A mesocosm experiment was used to investigate whether the consumption rate and functional response of P. colias differs for these two prey types in the presence and absence of habitat complexity. Results indicated that the mobile fish prey, F. lapillum benefitted from the refuges provided by complexity and suffered lower consumption rates, whereas the sedentary crab, H. rotundifrons did not. Finally, using a simple population model, the trade-off between prey abundance and predation success on the population dynamics of P. colias with and without habitat complexity was explored. Models showed that scenarios with complex macroalgal habitats generally support more predators, and faster population growth rates than scenarios lacking habitat complexity. However, scenarios with complex habitats were predicted to be more sensitive to fishing pressure and have the potential to be more vulnerable to overexploitation. These results highlight the importance of understanding how habitat complexity mediates relationships between commercially important fishery species and their prey, in order to understand how habitat loss may alter their foraging success and population dynamics.</p>

The consequences of complex habitat loss for the New Zealand blue cod, Parapercis colias

<p>Climate driven threats are predicted to decrease the complexity of biogenic habitats. Within temperate coastal marine environments, we know that complex macroalgal beds support more complex communities through the provision of microhabitats and refuges. Macroalgal habitats have potential interacting benefits and costs for predators, as increased macroalgal biomass supports higher richness and diversity of prey species, but prey within these habitats might be more difficult to catch. An important New Zealand fishery species, the blue cod (Parapercis colias), is a large bodied temperate reef fish found exclusively throughout the coastal waters of New Zealand. Its dependence on subtidal coastal reef environments mean that it is important to understand how a loss of complex macroalgal habitats might alter the way that blue cod forage, and how the trade-off between prey abundance and availability will affect its abundance and productivity. This thesis aims to understand the influence of complex macroalgal habitats on P. colias prey availability and behaviour, on the foraging success of P. colias, and ultimately on P. colias population dynamics. Experiments were conducted using choice chambers to evaluate whether two alternate P. colias prey, Forsterygion lapillum and Heterozius rotundifrons, showed a preference for complex habitats with and without predation risk. Both species preferred complex habitats in the absence of predation cues, but F. lapillum showed a more consistent preference for complexity in response to predation risk. A mesocosm experiment was used to investigate whether the consumption rate and functional response of P. colias differs for these two prey types in the presence and absence of habitat complexity. Results indicated that the mobile fish prey, F. lapillum benefitted from the refuges provided by complexity and suffered lower consumption rates, whereas the sedentary crab, H. rotundifrons did not. Finally, using a simple population model, the trade-off between prey abundance and predation success on the population dynamics of P. colias with and without habitat complexity was explored. Models showed that scenarios with complex macroalgal habitats generally support more predators, and faster population growth rates than scenarios lacking habitat complexity. However, scenarios with complex habitats were predicted to be more sensitive to fishing pressure and have the potential to be more vulnerable to overexploitation. These results highlight the importance of understanding how habitat complexity mediates relationships between commercially important fishery species and their prey, in order to understand how habitat loss may alter their foraging success and population dynamics.</p>

An Evaluation of Prior Residency and Habitat Effects on the Persistence of Settling Reef Fishes

<p>Both habitat complexity and competitive interactions can shape patterns of distribution and abundance of species. I evaluated the separate and joint effects of competitive interactions and habitat complexity on the survival of young fishes (Family Labridae) on coral reefs. First, I developed (in Chapter 2) a quantitative approach to evaluate potential resource (i.e., niche) overlap among groups of co-occurring species. Using appropriate transformations and probability models, I show that different types of data (e.g., categorical, continuous, count or binary data, as well as electivity scores) give rise to a standard measure of niche overlap, with the overlap statistic between two species defined as the overlapping area between the distributions for each species. Measurements derived from different types of data can be combined into a single multivariate analysis of niche overlap by averaging over multiple axes. I then describe null model permutation tests that differentiate between species occupying similar and different niches within my unified indices. I then implemented this approach (in Chapter 3) to evaluate potential habitat overlap among eight species of wrasse (Gomphosus varius, Halichoeres hortulanus, H. trimaculatus, Pseudocheilinus hexataenia, Scarus sordidus, Stethojulis bandanensis, Thalassoma hardwicke and T. quinquevittatum), and used these results to inform my subsequent field experiments. In a field assay, I identified the presence of T. quinquevittatum as having the greatest negative effect on survival of transplanted T. hardwicke from a suite of three candidate species which were most similar in habitat use to T. hardwicke (the other two candidate species were G. varius and P. hexataenia). In a subsequent field experiment, I tested how competition with T. quinquevittatum and structural refuge interact to influence the postsettlement survival of T. hardwicke. Competition with T. quinquevittatum and structural refuge both altered the survival of T. hardwicke, although their effects were not interactive, indicating that structural complexity did not mitigate the negative effects of competition. Survival of T. hardwicke was 2.3 times greater in treatments without T. quinquevittatum relative to those with T. quinquevittatum, and 2.8 times greater in treatments with structural refuge relative to treatments without structural refuge. Thalassoma hardwicke and T. quinquevittatum often enter reef communities asynchronously, resulting in competitive pressures faced by earlyarriving individuals that potentially differ from those experienced by late-arriving individuals. In a series of field experiments, I investigated whether the strength of intra-cohort competitive interactions between recent T. hardwicke and T. quinquevittatum settlers were dependent upon the sequence and temporal separation of their arrival into communities. Survival rates for both species were greatest in the absence of competitors, but when competitors were present, survival rates were maximized when competitors arrived simultaneously. Survival rates declined as each species entered the community progressively later than its competitor. Further, reversals in the sequence of arrival reversed competitive outcomes. Results provide empirical evidence for competitive lotteries in the maintenance of species diversity in demographically open marine systems, while also highlighting the importance of temporal variation in the direction and magnitude of interaction strengths. To further our understanding of how timing of arrival influences interaction strengths, I tested whether increasing the availability of complex habitat attenuates or enhances timing-of-arrival effects. Results from this field experiment indicated that aggression by early-arriving individuals towards late-arriving individuals increased as arrival times diverged. When aggression was weak, subordinate individuals were not displaced from complex habitat. Experimental increases in the availability of complex habitat resulted in increased survival of subordinates, presumably by disrupting predation pressure. However, when aggression was intense, competitive subordinates were displaced from complex habitat (regardless of the amount of complex habitat available), and this likely increased their exposure to predators. Overall, the experimental and observational components of this thesis emphasise heterogeneity in competitive environments experienced by recently settled reef fishes. These results highlight the important role that priority effects and habitat complexity play in determining the persistence of reef fish settlers, and illustrate how ecological contexts can add considerable variation to realised interaction strengths.</p>

An Evaluation of Prior Residency and Habitat Effects on the Persistence of Settling Reef Fishes

<p>Both habitat complexity and competitive interactions can shape patterns of distribution and abundance of species. I evaluated the separate and joint effects of competitive interactions and habitat complexity on the survival of young fishes (Family Labridae) on coral reefs. First, I developed (in Chapter 2) a quantitative approach to evaluate potential resource (i.e., niche) overlap among groups of co-occurring species. Using appropriate transformations and probability models, I show that different types of data (e.g., categorical, continuous, count or binary data, as well as electivity scores) give rise to a standard measure of niche overlap, with the overlap statistic between two species defined as the overlapping area between the distributions for each species. Measurements derived from different types of data can be combined into a single multivariate analysis of niche overlap by averaging over multiple axes. I then describe null model permutation tests that differentiate between species occupying similar and different niches within my unified indices. I then implemented this approach (in Chapter 3) to evaluate potential habitat overlap among eight species of wrasse (Gomphosus varius, Halichoeres hortulanus, H. trimaculatus, Pseudocheilinus hexataenia, Scarus sordidus, Stethojulis bandanensis, Thalassoma hardwicke and T. quinquevittatum), and used these results to inform my subsequent field experiments. In a field assay, I identified the presence of T. quinquevittatum as having the greatest negative effect on survival of transplanted T. hardwicke from a suite of three candidate species which were most similar in habitat use to T. hardwicke (the other two candidate species were G. varius and P. hexataenia). In a subsequent field experiment, I tested how competition with T. quinquevittatum and structural refuge interact to influence the postsettlement survival of T. hardwicke. Competition with T. quinquevittatum and structural refuge both altered the survival of T. hardwicke, although their effects were not interactive, indicating that structural complexity did not mitigate the negative effects of competition. Survival of T. hardwicke was 2.3 times greater in treatments without T. quinquevittatum relative to those with T. quinquevittatum, and 2.8 times greater in treatments with structural refuge relative to treatments without structural refuge. Thalassoma hardwicke and T. quinquevittatum often enter reef communities asynchronously, resulting in competitive pressures faced by earlyarriving individuals that potentially differ from those experienced by late-arriving individuals. In a series of field experiments, I investigated whether the strength of intra-cohort competitive interactions between recent T. hardwicke and T. quinquevittatum settlers were dependent upon the sequence and temporal separation of their arrival into communities. Survival rates for both species were greatest in the absence of competitors, but when competitors were present, survival rates were maximized when competitors arrived simultaneously. Survival rates declined as each species entered the community progressively later than its competitor. Further, reversals in the sequence of arrival reversed competitive outcomes. Results provide empirical evidence for competitive lotteries in the maintenance of species diversity in demographically open marine systems, while also highlighting the importance of temporal variation in the direction and magnitude of interaction strengths. To further our understanding of how timing of arrival influences interaction strengths, I tested whether increasing the availability of complex habitat attenuates or enhances timing-of-arrival effects. Results from this field experiment indicated that aggression by early-arriving individuals towards late-arriving individuals increased as arrival times diverged. When aggression was weak, subordinate individuals were not displaced from complex habitat. Experimental increases in the availability of complex habitat resulted in increased survival of subordinates, presumably by disrupting predation pressure. However, when aggression was intense, competitive subordinates were displaced from complex habitat (regardless of the amount of complex habitat available), and this likely increased their exposure to predators. Overall, the experimental and observational components of this thesis emphasise heterogeneity in competitive environments experienced by recently settled reef fishes. These results highlight the important role that priority effects and habitat complexity play in determining the persistence of reef fish settlers, and illustrate how ecological contexts can add considerable variation to realised interaction strengths.</p>

Habitat Complexity Affects the Structure but Not the Diversity of Sessile Communities on Tropical Coastal Infrastructure

Increasing human population, urbanisation, and climate change have resulted in the proliferation of hard coastal infrastructure such as seawalls and breakwaters. There is increasing impetus to create multifunctional coastal defence structures with the primary function of protecting people and property in addition to providing habitat for marine organisms through eco-engineering - a nature-based solutions approach. In this study, the independent and synergistic effects of physical complexity and seeding with native oysters in promoting diversity and abundances of sessile organisms were assessed at two locations on Penang Island, Malaysia. Concrete tiles with varying physical and biological complexity (flat, 2.5 cm ridges and crevices, and 5 cm ridges and crevices that were seeded or unseeded with oysters) were deployed and monitored over 12 months. The survival of the seeded oysters was not correlated with physical complexity. The addition of physical and biological complexity interacted to promote distinct community assemblages, but did not consistently increase the richness, diversity, or abundances of sessile organisms through time. These results indicate that complexity, whether physical or biological, is only one of many influences on biodiversity on coastal infrastructure. Eco-engineering interventions that have been reported to be effective in other regions may not work as effectively in others due to the highly dynamic conditions in coastal environment. Thus, it is important that other factors such as the local species pools, environmental setting (e.g., wave action), biological factors (e.g., predators), and anthropogenic stressors (e.g., pollution) should also be considered when designing habitat enhancements. Such factors acting individually or synergistically could potentially affect the outcomes of any planned eco-engineering interventions.