Conditions for dispersal and endemism of montane forest birds on isolated volcanoes in Southern Luzon, Philippines

Professorial Chair Lecture

UPLB Faculty, Staff and Students Professorial Chair Lecture

Place

UPLB CAS Auditorium

Date

11-23-2004

Abstract

The rugged mountainous terrain of the Philippine islands produces altitudinal gradients in its vegetation that separate the mountain avifauna into highland and lowland groups. Where even sympatric congeners may occur within gradients, but for allopatric congeners to avoid competition to become restricted and specialized to their montane habitats. Generally, most montane avifauna are poor, given the constraints of a single forest stratum, no free water and harsh cold climates that also limit plant diversity. A fraction of the birds are either migrants or cosmopolitan and do not represent typical montane species. It is a fact that bird species diversity decreases with increasing altitude, but the greater restriction contributes to endemism, forming unique taxa within a mountain range. However, on more isolated volcanic formations rarely joined only at base, and often separated by wide alluvial plains, this restricts dispersal of montane birds to adjacent peaks. What conditions are necessary for montane birds to persist? What are the limitations that restrict their dispersal? This paper aims to compare the distribution of birds along three isolated peaks in Southern Luzon. Observations of birds using standard methods were recorded from montane forest sites on three dormant volcanoes - Mount Banahao, Mount Maquiling and Mount Malinao.

The distribution of highland birds along isolated volcanoes in Southern Luzon are more limited by altitude and climate, than by vegetation type. Tall mountain massifs (c. 2,000 m) like Mount Banahao and Mount Isarog have extensive montane forests thus harbor more typical highland species than in lower peaks (c. 1,000 m) like Mount Maquiling. Although, Mount Maquiling contains cloud forest vegetation on its peaks, only a few highland birds were present, and instead were replaced by lowland farms. Mountains of intermediate height (c. 1,5000 m) like Mount Malinao have a rich montane avifauna similar to those found in higher peaks, but not as diverse. Apparently, the persistence of both highland and lowland birds on Mount Malinao indicated that the mountain was sufficiently high to meet the lower altitudinal limits required by typical montane species for dispersal. Isolation due to sea level rise contribute to subspecific endemism between related Pleistocene islands, and that mountains also serve as barriers within islands, separating populations.

On isolated volcanic peaks, montane birds restricted by altitude and habitat gradients, are likely to diverge. Despite this, birds found in the Bicol peninsula appear to belong to the same race and possibly resulted from Pleistocene colonization, only recently isolated. Most montane birds are restrictive, and only a few are able to disperse into transitional forests (c. 500 m), rarely lower. Further comparative behavioral or bioacoustic (and genetic) studies of isolated populations from these volcanic peaks may help determine the degree of relatedness of birds inhabiting mountains within the peninsula. Variability in the distribution of montane birds were observed between mountains of Bicol (Mounts Molinao & Isarog) and Southern Tagalog (Mounts Banahao & Maquiling), wherein peninsular isolation limits dispersal of endemic Bicol races northward. Differences in tectonic plates and the wide lowland isthmus between the Southern Tagalog rim and Bicol chain ma contribute to this restriction, but still some persistently shared forms reveal past Pleistocene connections within Southern Luzon.

Location

UPLB Main Library Special Collections Section (USCS)

College

College of Arts and Sciences (CAS)

Language

English

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