Browsing by Subject "Philippines"

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    Biodiversity and arthropod abundance in the upland of Leyte, Philippines
    (2005) Szinicz, Gundula; Sauerborn, Joachim
    In the humid tropics of SE-Asia the last primary forests are dwindling at an alarming rate. In many regions cultivated and degraded land outnumbers by far natural ecosystems. In the upland of Leyte island this is due to commercial and illegal logging activities and intensive slash-and-burn agriculture. The loss of the natural vegetation cover is accompanied by a decrease in diversity of fauna and flora, consequently also in ecosystem services and interactions, thus destabilizing the system and finally leading to degradation. To further preserve and restore natural biodiversity landscapes dominated by man need to be included in an overall research strategy. So far only few studies focus on the biodiversity of cleared and converted land adjacent to natural areas in the tropics. This study was conducted in a Philippine upland area and focused on interchanges of insects between the natural and the managed landscape. Two questions were approached. (1) Which structures and components of the cultural landscape are of significance for conserving arthropod biodiversity, and (2) are there species which originate from the natural forest and are able to become resident in the man-made systems? In order to answer these questions insect- and plant surveys as well as the movement patterns of selected insect species were examined along a gradient from the natural forest through the agricultural land. So as to define the effects of habitat destruction on the arthropod community of the research area arthropod communities of different habitats between the natural and agricultural ecosystems with increasing distance to the forest, in relation to the vegetation were compared. Insect sampling was carried out using modified Malaise traps, whereby four habitats were considered: (a) forest interior, (b) forest margin, (c) vegetable fields and (d) chayote ((Sechium edule (Jacq.) Sw. (Cucurbitaceae); the only perennial vegetable of the area) fields. These traps allowed a separate catch for each of the two arrival sides, whereby the one was always opened to the forest and the other to the field. Trapping was set up for a total of 18 months in 2001 and 2002 at three sites with the four habitats each. Arthropod diversity, composition of the arthropod community and trophic guild composition at habitats were determined for each habitat and arrival side. Obtained results are presented and discussed with regard to first: arthropod diversity and community composition along the transect from natural through agricultural systems; second: abundance patterns of selected species in natural and agricultural systems and third: abundance patterns of selected species within the agricultural land. It was found that plant diversity, vegetation structure and taxonomic composition as well as differences in the turnover of the vegetation at habitats (productivity of vegetation) influence arthropod groups and species in the study area in different ways which could not be generalised. Further, the relationships of insects between the natural forest and the open agricultural land were considered. In order to identify species that occur in the forest as well as in the open country, first, insects at sites of the forest interior, the forest margin and the agricultural land, were recorded using modified Malaise traps. Then, movement patterns of selected species were determined based on their abundances at the different habitats and arrival sides. In addition it was tried to find out whether major pest species of the cultivated crops show any relationship to the adjacent natural forest, and whether species originating from the forest (non-pest species) are able to colonize open country. The results indicate that the habitat of the pest species considered is limited to the cultivated land and does not include the forest. None of the non-pest species recorded in this study would be able to exist permanently in the agricultural area. They all depend on a closed forest habitat and therefore will become extinct as the forest disappears with proceeding slash-and-burn agriculture. However, some but not all of the pest and forest species were regularly recorded from the forest margin. Finally it was focused on relationships of insects between perennial and consecutive changing vegetable crops. Two kinds of habitats were distinguished: (i) frequently disturbed and rotational changing vegetables with simple architecture; (ii) rarely disturbed stands of chayote, with complex architecture. The impact of changing crop and weed species composition and the agricultural practices (soil preparation, planting, weeding, harvest) applied on the abundance of selected insect species and the question whether stands of chayote are used as refuge as long as conditions in the seasonal vegetables become unfavourable due to agroecosystem management applied were analysed. The insect species investigated include phytophagous specialists and generalists as well as beneficials (predators and pollinators). It only was possible to generalize movement patterns regarding significance of abundance variations at habitats and at opposite arrival sides of the traps in each habitat. With respect to the population development of the species in relation to cropping patterns and agricultural practices applied no common patterns could be determined. The results contribute to the assessment of the effects of man-made habitat conversion on the arthropod fauna in tropical ecosystems. The identification and classification of habitats and their interactions might enhance the understanding of ecosystems in order to make aware the need to preserve and restore biodiversity.
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    Seasonal variation in growth, quantitative and qualitative food consumption of milkfish, Chanos chanos (Forsskål 1775), and Nile tilapia, Oreochromis niloticus (L. 1758), in Laguna de Bay, Philippines
    (2002) Richter, Hartmut; Becker, Klaus
    Laguna de Bay, the largest lake in the Philippines, lies directly southeast of the capital Manila. The lake has a mean depth of only 2.8m and a muddy bottom which is stirred during windy weather, causing turbid conditions (Secchi depth <30cm). In the dry season, the water level drops below that of the nearby sea, leading to a backflow of saline water which clears the water until the return of the monsoon winds (Secchi depth >100cm) and leads to algal blooms. Since the beginning of the 1970s, the lake has been used for culturing milkfish, Chanos chanos (Forsskål), in large netpens (max. 2000ha) and Nile tilapia, Oreochromis niloticus (L.), in smaller cages (max. 200m2). Initially, it was possible during the algal blooms to grow fish from fingerling (ca. 10g) to marketable size (ca. 200g) in three months, making two harvests a year possible. Aquaculture quickly spread until in the middle of the eighties, over a third of the lake was covered with cages. At the same time the growth of the fish declined, which was attributed to the excessive use of primary production. Since then, despite a reduction in aquaculture coverage to the generally recommended level of 10% of the lake, fish growth has never reached the levels of the early days of culture. In the present work, seasonal variation in growth, feeding spectrum and daily ration of these two species was to be investigated in relation to water quality in order to find out more about the interaction between aquaculture and the lake. Between May 1995 and August 1997, milkfish and tilapia were sampled on several occasions at commercial operations over the 24-hour cycle. Since milkfish, unlike tilapia, do not receive supplemental feed, the proportion of their growth derived only from natural food could be determined from the cultured fish. Tilapia were kept in cages without feed specially for this purpose and measured and weighed twice a month between March and November 1997. At the same time, selective water quality parameters (particulate organic and inorganic matter, Chlorophyll-a, zooplankton) were analysed weekly. The growth of unfed fish was significantly faster between saltwater intrusion (mid-May) and the return of the monsoons (late July) than at other times of the year. On the other hand, food consumption was only slightly higher in tilapia when the water was clear than at other times and in milkfish hardly differed over the year. Both species mainly fed on amorphous organic detritus; significant levels of phytoplankton were only found in the stomachs at times of algal bloom. In supplemented tilapia, the daily ration still consisted of 35-75% natural food, suggesting that pelleted feed was used inefficiently. The main factor limiting fish growth therefore seemed to be food quality since detritus has often been shown to be poor quality food. The weekly water samples collected in 1997 demonstrated that the total level of phytoplankton was not necessarily higher at times of rapid fish growth. The main difference was related to algal size, since at times of turbid water, small diatoms dominated but these were replaced by larger blue-green algae after saltwater intrusion. In conjunction with the feeding method of these fish, the strongly seasonal growth of the fish could now be explained. Phytoplanktivorous fish such as milkfish and tilapia can only select their food on the basis of size. Since the organic detritus in the lake consisted of particles smaller than 15µm, it was possible for the fish to selectively filter larger blue-green algae but not smaller diatoms. This could also explain why fish growth rates did not recover after a reduction in aquaculture in the mid-eighties, since the relationship between the level of algae and that of detritus seems to be more important than total algal biomass. In order to increase production to those levels found in the early seventies, the level of detritus in the lake would have to be reduced, for which its origin would have to be investigated first.
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    Vitamin A and iron consumption and the role of indigenous vegetables: a household level analysis in the Philippines
    (2006) Weinberger, Katinka; Qaim, Matin; Ecker, Olivier; Hönicke, Mireille
    Micronutrient malnutrition is a public health problem in many regions of the developing world. Severe vitamin A and iron deficiencies are of particular concern due to their high prevalence and their serious, multiple health effects on humans. This paper examines dietary patterns and nutrient intakes, as well as their socioeconomic determinants among households in the Philippines. Since promotion of indigenous vegetables is often considered as an avenue to reduce micronutrient malnutrition, special emphasis is placed on analyzing the contribution of this particular food group to household vitamin A and iron intakes. We use a sample consisting of 172 resource-poor households located in peri-urban areas of Laguna Province. A 24-hour food consumption recall allows for detailed, meal-specific examination of diets. Results of the dietary analysis suggest that fish is of major importance for vitamin A and iron intakes. But also vegetables, and especially indigenous vegetables, play an essential role for balanced household diets. In order to determine socioeconomic factors influencing vitamin A and iron intakes, we employ an econometric model, which shows that deficiencies are strongly associated with low household incomes and poverty. Thus, poverty alleviation will help reduce the problem of micronutrient malnutrition in the medium and long run. However, in the interim, more targeted interventions will be needed. Our results suggest that promotion of indigenous vegetables can play a role in this respect, especially among the poor, who can often not afford sufficient amounts of animal products.