Diminuição das estruturas dispersivas em áreas urbanas: efeito da urbanização sobre traços funcionais de dispersão de plantas espontâneas

Abstract

Urbanization is one of the main drivers of landscape modification, altering natural conditions, and challenging species persistence causing taxonomic and functional homogenization. Different places along the impervious urban matrix offer conditions for the establishment of spontaneous vegetation, as wasteland and sidewalks cracks, and their ability to colonize these areas is dependent on the dispersal process. Propagule dispersal characteristics evolved through interactions with local environmental conditions and biodiversity interaction, and hence environmental changes could impact these traits. The aim of this work was to evaluate the effect of urbanization on the dispersal functional traits of spontaneous plants. We investigated (i) the effect of urbanization intensity to plant height, and the quantity, size, and weight of fruits and seeds; (ii) the difference in functional traits of plants with different dispersal syndromes and invasion status; and (iii) the effect of urbanization on the ratio of species within each dispersal syndrome. Data collection was undertaken in the city of Lavras (Minas Gerais, Brazil), where we classified urbanization intensity at the district scale, defined by the percentage paved area: very low (0-15%), low (25-40%), moderate (50-75%) and high (75-90%). Within each class, we projected three circular sampling areas (r=200m), in which we distributed 10 1m² quadrats to collect material. Data were analyzed using generalized linear mixed models (GLMM) to evaluate the variation in the traits as a function of the percentage of paved area. We identified 88 plant species in total, 43 natives, 24 exotic naturalized and 21 exotic invaders. We found a negative relationship between urbanization intensity and the values of the functional traits measured. The values of height of plants general community, autochory species, and invasive exotic species were smaller in more urbanized areas. Anemochoric plants showed a decrease in fruit size in more urban areas, whereas zoochoric species showed a decrease in fruit and seed weight. Also in more urban areas, native species showed a reduction in fruit quantity and size, whereas naturalized species showed a decrease in seed quantity. There was no variation in species ratio by dispersal syndrome at different classes of urbanization. Our results demonstrate that the reduction in dispersal functional traits values could mean better adaptation to urbanized areas because of a reduction of quantity and size of germination locations.