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Abstract. Island biogeography theory predicts that species richness increases with habitat area and declines with isolation. We expand this framework to address changes in the number of links and species in pollination webs from 12 isolated hills, ranging in area from tens to thousands of hectares, immersed in the agriculture matrix of the Argentine Pampas. We also studied whether total interaction frequency is partitioned more evenly among individual links in richer webs. Our results reveal a direct effect of area on the number of links and species present in each pollination web. However, link richness increased twofold faster than species richness with area. These area effects were not confounded by sampling effort or correlated incidence of exotic species, despite widespread habitat disturbance. Habitat proximity, an inverse measure of isolation, had a marginally significant influence on link but not on species richness. Increased link number was associated with decreasing dominance by any particular interaction and increasing interaction evenness. Despite the strong area effect, a rich pollination web sampled from a small, protected sierra suggests that simple conservation measures, such as reduced grazing and fire suppression, may effectively preserve much local interaction diversity.

Abstract. In order to test for cumulative effects of fire on Paspalum quadrifarium‐dominated grasslands (‘pajonal’), we analysed the impact of single and repeated fires on the community structure and post‐fire recovery of canopy after a final, simultaneous fire event. Nine plots were defined within a homogeneous pajonal stand, and treatments of low (LF), medium (MF) and high frequency (HF) of fire were defined by the application of one, two or four cold‐season burns, respectively, along a 6‐yr period. Both burned and unburned plots were exposed to grazing by cattle during the summer following the first and the third years of that period. High cattle preference for burned sites conditioned fire temperature and vegetation responses to the following burning events. Cumulative effects between successive burning events were observed for the cover of basal area of the dominant and other sprouting species, the cover and thickness of the litter layer, the seed bank size of the principal recruiter species, and the floristic composition. While light interception by the canopy was positively related to fire frequency during the early growth season, further growth of P. quadrifarium determined a greater light interception in LF than in MF and HF. These patterns of light interception were associated with a faster occupation of the inter‐tussock areas by opportunistic species in plots subjected to frequent fires (HF and MF) than in plots with low fire frequency (LF), and a more lasting regrowth of P. quadrifarium in the LF plot than in the HF ones. High fire frequencies reduced the dominance of P. quadrifarium. Percent of species classified as subordinated graminoids or forbs did not vary among treatments. However, the abundance of different forb species was differentially favoured by contrasting frequencies of fire, describing some coarse relationships between their specific responses and their dispersal strategies.

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