Modeling the effects of trait-mediated dispersal on coexistence of mutualists

© 2020 the Author(s), licensee AIMS Press. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0) Even though mutualistic interactions are ubiquitous in nature, we are still far from making good predictions about the fate of mutualistic communities under threats such as habitat fragmentation and climate change. Fragmentation often causes declines in abundance of a species due to increased susceptibility to edge effects between remnant habitat patches and lower quality “matrix” surrounding these focal patches. It has been argued that ecological communities are replete with trait-mediated indirect effects, and that these effects may sometimes contribute more to the dynamics of a population than direct density-mediated effects, e.g., lowering an organism\u27s fitness through competitive interactions. Although some studies have focused on trait-mediated behavior such as trait-mediated dispersal, in which an organism changes its dispersal patterns due to the presence of another species, they have been mostly limited to predator-prey systems-little is known regarding their effect on other interaction systems such as mutualism. Here, we explore consequences of fragmentation and trait-mediated dispersal on coexistence of a system of two mutualists by employing a model built upon the reaction diffusion framework. To distinguish between trait-mediated dispersal and density-mediated effects, we isolate effects of trait-mediated dispersal on the mutualistic system by excluding any direct density-mediated effects in the model. Our results demonstrate that fragmentation and trait-mediated dispersal can have important impacts on coexistence of mutualists. Specifically, one species can be better able to invade and persist than the other and be crucial to the success of the other species in the patch. Matrix quality degradation can also bring about a complete reversal of the role of which species is supporting the other\u27s persistence in the patch, even as the patch size remains constant. As most mutualistic relationships are identified based on density-mediated effects, such an effect may be easily overlooked

A Perspective on Management of House crow (Corvus splendens) in the City of Colombo

House crow (Corvus splendens) is considered as a nuisance animal in the City of Colombo. A roost count method was employed to determine the population size of house crow and their distribution in different wards of the city. Main and link roads of the 47 wards of the city were patrolled during early evening hours to take population counts. Also, direct observations were done to study the biological enemies of crows during day and night. In addition, day time census of house crow and assessment of availability of open garbage dumps was carried out in three selected wards. Current population size of house crow in the City of Colombo was estimated as 101,100 (2018). Using the previous population estimates of crows in the city; 1980-50,000 (Subasinghe and Samad); 1992-70,000 (Dayawansa and Kotagama); 2001-118,500 (Keeragala and Dayawansa), 2006-124,330 (Dayawansa et al.) and 2012-98,350 (Dayawansa unpublished); a population growth curve was constructed. Population growth depicted a logistic model and rate of growth (r) determined by a differential equation depicted three distinct phases on the sigmoid curve and a carrying capacity (K). A positive significant relationship between availability of food resources (garbage) and crow abundance was evident (Linear Regression p<0.05). A positive correlation between availability of trees and crow abundance was evident, however, it was not statistically significant. Total number of roosts has increased significantly from 1992 to 2018 due to increased occurrence of small and medium roosts (One-Way ANOVA: p<0.05). Ironically, there is a decrease of occurrence of very large roosts and large roosts. Variety of trees occupied as roosting sites has increased from 34 to 46 species from 1992 to 2018. House crow population has shown a logistic growth and reached a carrying capacity due to limited availability of resources such as food and breeding sites. It was observed that crows avoid occupying areas where Brown hawk owls inhabit. Control of population size of house crow could be satisfactorily done by manipulating the availability of food resources by implementing an efficient garbage management strategy in the city. In addition, augmenting the top levels of the trophic pyramid by supporting the abundance of nocturnal predators such as Brown hawk owl and Barn owl can reduce the crow populations. Implementation of artificial population control methods such as destroying eggs and culling of adults would be thoroughly unnecessary to control House Crow population in the City of Colombo.Keywords: House Crow, Nuisance species, Logistic growth model, Population managemen

Staging of lung cancer in a tertiary care setting in Sri Lanka, using TNM 7th edition. A comparison against TNM6

<p>Abstract</p> <p>Background</p> <p>Lung cancer is a leading cause of cancer-related mortality in Sri Lanka and throughout the world. The latest staging system for lung cancer is the tumor node metastasis (TNM) 7^thedition in which there are major changes to the previous version. The objective of our study was to find out the implications of TNM7^thedition on lung cancer staging in a resource limited setting, and to compare it with the previous TNM 6^thedition.</p> <p>Methods</p> <p>Patients with histologically proven lung cancer consecutively presented to respiratory unit of Teaching Hospital Kandy, Sri Lanka were recruited to the study over a period of one year from April 2010 to March 2011. They were staged using CT, ultrasound scan of abdomen, bronchoscopy and CT spine and brain when necessary. Staging was done using TNM 7 as well as TNM6. Surgical or non-surgical treatment arms were decided on staging and the number of patients in each treatment arm was compared between the two staging systems.</p> <p>Results</p> <p>Out of 62 patients, thirty four patients (54%) had metastatic disease and 19 (30%) of them had pleural effusions (M1a), while 15 (24%) had distant metastasis (M1b). When compared to TNM6 there was no difference in the number of patients in T1 category, but the number in T2 was higher in TNM7 (25 Vs 20). Similarly the number in T3 group was higher in TNM7 (11 Vs 5) and the number in M category was doubled (34 Vs 17 [Chi-6.46, <it>p </it>= 0.011]) compared to TNM 6. The number of patients suitable for surgery were 17(27.5%) in TNM 7 and 18(29%) [Chi-0.02, <it>p </it>= 0.88] in TNM6.</p> <p>Conclusions</p> <p>This study shows that a significant proportion of patients were having advanced disease with distant metastasis on presentation. The number of patients falling to stage IV is significantly higher when staged with TNM7 but there was no significant difference in the number of patients undergoing surgery when TNM 7 was used compared to TNM6.</p

Community based conservation as a tool to conserve freshwater fish in Sri Lanka: Evidence from Puntius bandula conservation programme

Puntius bandula is an endemic fish restricted to two unprotected small streams at Galapitamada. The streams are surrounded by habitats subjected to frequent anthropogenic threats such as destruction of floral assemblages of the catchment and stream banks, releasing of agrochemicals, fertilizers and kitchen waste, artificial constructions of the stream bank, narrowing of the stream and collapsing of the stream bank due to expanding paddy cultivations and illegal collection of fish by unauthorized parties. The population size of P. bandula has declined rapidly during the past two decades making it a Critically Endangered species. The main aim of this programme was to ensure long term survival of this species through a participatory conservation approach. First, a standardized questionnaire survey was done to determine the degree of awareness, the willingness of the community to conserve P. bandula, obtain a profile of the community and to introduce the objectives of the programme. Further, awareness was raised in the community through presentations and discussions held at monthly community meetings. An environment protection committee was established and an action plan was drawn up. Under this; two community awareness workshops, transect walk, school environment programmes and monthly community meetings were conducted. Further, several communication tools such as calendars, a brochure, a time table, powerpoint presentations, video clips and sign boards were produced. The degree of awareness of the community was increased up to 85% after the awareness programme from 54%. Also a tree planting campaign was conducted with the community to enhance the habitat of P. bandula. Finally a small stock of adult P. bandula (15 females and 5 males) was translocated to a new locality as a participatory approach to establish a second population and 10 adults and 7 fry were observed in the new locality three months after the translocation. It can be concluded that, this approach is useful in conserving endemic freshwater fish species in Sri Lanka by minimizing threats via self awareness, since most of them are located outside of the protected area net work and subjected to anthropogenic threats

Modeling the effects of trait-mediated dispersal on coexistence of mutualists

Even though mutualistic interactions are ubiquitous in nature, we are still far from making good predictions about the fate of mutualistic communities under threats such as habitat fragmentation and climate change. Fragmentation often causes declines in abundance of a species due to increased susceptibility to edge effects between remnant habitat patches and lower quality "matrix" surrounding these focal patches. It has been argued that ecological communities are replete with trait-mediated indirect effects, and that these effects may sometimes contribute more to the dynamics of a population than direct density-mediated effects, e.g., lowering an organism's fitness through competitive interactions. Although some studies have focused on trait-mediated behavior such as trait-mediated dispersal, in which an organism changes its dispersal patterns due to the presence of another species, they have been mostly limited to predator-prey systems-little is known regarding their effect on other interaction systems such as mutualism. Here, we explore consequences of fragmentation and trait-mediated dispersal on coexistence of a system of two mutualists by employing a model built upon the reaction diffusion framework. To distinguish between trait-mediated dispersal and density-mediated effects, we isolate effects of trait-mediated dispersal on the mutualistic system by excluding any direct density mediated effects in the model. Our results demonstrate that fragmentation and trait-mediated dispersal can have important impacts on coexistence of mutualists. Specifically, one species can be better able to invade and persist than the other and be crucial to the success of the other species in the patch. Matrix quality degradation can also bring about a complete reversal of the role of which species is supporting the other's persistence in the patch, even as the patch size remains constant. As most mutualistic relationships are identified based on density-mediated effects, such an effect may be easily overlooked