Date

September 24, 2012

Time

4:00 pm

Location

UTSC, SW403

Julie Helson, Exit Seminar

Host: Dudley Williams

ABSTRACT

Tropical freshwater ecosystems are understudied and not well

understood; however, they are becoming increasingly imperiled by

escalating anthropogenic impacts. The aim of this thesis was to

investigate how tropical freshwater macroinvertebrate communities

changed both structurally and functionally over a pristine-rural-urban

land-use gradient, in relation to different spatial and temporal

scales, as well as to the availability of potential food sources.

Fifteen streams in the Panama Canal Watershed were sampled during the

dry and wet seasons of 2007 and 2008, for macroinvertebrate

communities (benthic and leaf litter), environmental variables, and

potential food sources. Along the land-use gradient, in both habitat

types, taxon richness, diversity, and evenness all decreased

significantly; whereas, abundance increased significantly. For the

benthic macroinvertebrate community, variation was explained equally

well by local (water chemistry and sediment type) and landscape

(riparian vegetation and watershed land use) characteristics in the

dry season, and landscape characteristics explained slightly more

variation in the wet season. Leaf-litter macroinvertebrate community

variation was better explained by local variables than by landscape

variables in both seasons. In terms of potential food resources, fine

detritus and inorganic material were the most common across all

streams (increased quantities in urban streams) and seasons; whereas,

the availability of diatoms and leaf material increased in the dry

season. Using gut content analyses, we found that collectors

(gatherers and filterers) were by far the most common functional

feeding group, increasing in abundance along the land-use gradient.

Predators, shredders, and scrapers were all most abundant in pristine

streams and decreased along the land-use gradient. Finally, using

seven community metrices, a potential biomonitoring tool was

developed, the Neotropical Low-land Stream Multimetric Index (NLSMI),

which distinguished well among the different levels of stream

impairment. This study demonstrated that tropical communities were

negatively affected by human land alteration, but that community

responses depended on the habitat sampled, the influence of different

spatial scales varied between the seasons, and the effect of food

resources appeared to be complex. These aspects must be taken into

consideration for management decisions and restoration strategies to

be effective.