Alexander Lees
Research interests and publications
Synergistic effects of forest disturbance and fragmentation on a species-rich Amazonian avifauna
juvenile Harpy Eage (Harpia harpyja), Alta Floresta, MT, Brazil, August 2005
FOREST FRAGMENTATION
The Amazon basin is experiencing the highest absolute rate of deforestation worldwide. My PhD thesis aimed to ascertain what the joint effects of habitat area, habitat isolation, and forest disturbance have on the persistence of bird populations in Amazonian forest fragments. These data sets have been used to ask questions such as:
How large does a forest fragment have to be to retain its original avian community (i.e. the Minimum Critical Area)?
- Which functional groups and species are most susceptible to the effects of forest fragmentation?
- Which species within the avian community are undisturbed forest interior specialists?
- How quickly do forest fragments lose these specialists?
- Conversely, which species are generalists and thus better adapted to forest fragmentation?
- Does proximity to other forest fragments (i.e. degree of isolation) affect rates of extinction?
- Does proximity to an area of contiguous forest affect local extinction rates?
By addressing these issues, the ultimate aim of the study was to discern the implications of forest fragmentation and fragment isolation to forest bird species. The study region 12,500 km2 landscape of Alta Floresta, northern Mato Grosso, Brazil, which shares an exceptionally species rich and largely homogeneous source fauna and includes hundreds of both disturbed and undisturbed forest fragments ranging in size from <1 to 13,500 ha, as well as vast tracts of continuous forest. The history of deforestation in this region dates from the early 1970’s, with little additional forest loss in recent decades. The extinction relaxation process within ‘old’ fragments could thus be assumed to have reached near-equilibrium conditions for most medium to large-bodied forest vertebrate taxa. This is supported by the apparent lack of dispersal opportunities and source-sink dynamics across the typically hostile intervening matrix consisting primarily of degraded pasture. Many cattle ranches in this region retain stricted protected or semi-protected forest patches, whereas most of the fragments within these ranches have been widely exposed to subsistence hunting by small farmers and extractive communities.
Lees, A.C. & Peres, C.A. 2008. Avian Life history determinants of local extinction risk in a fragmented neotropical forest landscape. Animal Conservation, 11: 128-137. PDF
Lees,
My 2005 field campaign made use of a point-count methodology for avifaunal and primate surveys and assessment of large mammal usage of corridors by recording tracks and signs (coupled with a thorough habitat assessment, using both ground-truthed data and satellite imagery) to ask the following questions:
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How does corridor width influence species composition? i.e. what biodiversity is captured at different corridor widths?
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How does corridor vegetative composition degree of preservation influence species presence/absence?
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How far along corridors do different species occur?
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How does landscape context influence species diversity in corridors?
The Brazillian Forestry Code determines fixed minumium widths of forest to be left alongside permenant water bodies, this work will both illustrate the value and extent of occurence of corridors within a model fragmented landscape and demonstrate the value of the forestry code.
Key Paper:
Lees, A.C. & Peres, C. 2008. Conservation value of remnant riparian forest corridors of varying quality for Amazonian birds and mammals. Conservation Biology, 22: 439-449 PDF
GAP CROSSING
One of the greatest challenges for conservation biologists in the 21st century is to accurately predict how the movement of fauna is influenced by landscape configuration and composition, thus understanding the responses of populations to habitat loss and fragmentation. “Gap crossing” may be defined as any movement by an organism across inhospitable terrain. For forest specialist birds such a reluctance to cross open areas may be a result of predation risk or innate avoidance of such areas in which they cannot identify familiar landscape elements.
Hyper-fragmented southern Amazonia provides numerous opportunities in which to observe the restrictions that subdivision of forest patches plays on bird movements. Responses are likely to be highly family and foraging-guild specific, with some groups already known to be able gap-crossers while others are inveterately gap-shy. My 2006 field-campaign focused on such gap-crossing behaviour across a range of gap-widths (4-400m) all located within substantial (>2000ha) forest sites.
Bare-eyed Antbird (Rhegmatorhina gymnops), Smooth-billed Ani (Crotophaga ani), White-browed Purpetuft (Iodopleura isabellae), Alta Floresta July 2006
Key Paper: