Species traits influence their response to environmental conditions and
the match between phenotypes and environment mediates spatial changes in
species composition. These trait-environment linkages can be disrupted
in human-modified landscapes. Human land-use creates habitat fragments
where dispersal limitation or edge effects can exclude species that may
otherwise suit a given macro-scale environment. Furthermore, stressful
micro-environments in fragments may limit viable trait combinations
resulting in stronger trait covariance compared to contiguous forest,
especially in harsher macroenvironments. In a wet tropical forest
landscape in the Western Ghats Biodiversity Hotspot of peninsular India,
I compared fragments with adjacent contiguous forest for signatures of
trait-mediated assembly of tree communities along macroenvironmental
gradients. Using four key plant traits—seed size, specific leaf area
(SLA), wood density, and maximum height—I evaluated changes in
trait-mediated abundances and trait covariance across environmental
gradients. Trait-mediated abundances primarily changed along the
elevation gradient in contiguous forest, smaller-seeded, shorter,
thinner-leaved species increased at higher elevations. In fragments,
higher SLA species increased in more seasonal climate and decreased with
higher precipitation, and larger seeds decreased at warmer sites.
However, traits only weakly predicted abundances and only contiguous
forests experienced significant compositional change via traits, driven
by trait syndromes varying along a composite environmental gradient
defined by elevation, water deficit, and soil C:N ratio. Covariance of
seed size and maximum height along gradients of precipitation and
temperature revealed divergent constraints on viable phenotypes in
fragments and contiguous forest. Notably, local biotic conditions
(functional diversity) had stronger effects than environment in
explaining trait covariance. Overall, the results imply that trait
syndromes and trait covariance, rather than single traits, determine the
phenotypes best suited to different macroenvironmental conditions and
should inform management or restoration goals in fragments.
Evolutionary History Impacts Phyllosphere Community Assembly on Forage Grasses
