Woody plant encroachment drives population declines in 20% of common open ecosystem bird species.

Grassy ecosystems cover more than 40% of the world's terrestrial surface, supporting crucial ecosystem services and unique biodiversity. These ecosystems have experienced major losses from conversion to agriculture with the remaining fragments threatened by global change. Woody plant encroachment, the increase in woody cover threatening grassy ecosystems, is a major global change symptom, shifting the composition, structure, and function of plant communities with concomitant effects on all biodiversity. To identify generalisable impacts of encroachment on biodiversity, we urgently need broad-scale studies on how species respond to woody cover change. Here, we make use of bird atlas, woody cover change data (between 2007 and 2016) and species traits, to assess: (1) population trends and woody cover responses using dynamic occupancy models; (2) how outcomes relate to habitat, diet and nesting traits; and (3) predictions of future occupancy trends, for 191 abundant, southern African bird species. We found that: (1) 63% (121) of species showed a decline in occupancy, with 18% (34) of species' declines correlated with increasing woody cover (i.e. losers). Only 2% (4) of species showed increasing population trends linked with increased woody cover (i.e. winners); (2) Open habitat specialist, invertivorous, ground nesting birds were the most frequent losers, however, we found no definitive evidence that the selected traits could predict outcomes; and (3) We predict open habitat loser species will take on average 52 years to experience 50% population declines with current rates of encroachment. Our results bring attention to concerning region-wide declining bird population trends and highlight woody plant encroachment as an important driver of bird population dynamics. Importantly, these findings should encourage improved management and restoration of our remaining grassy ecosystems. Furthermore, our findings show the importance of lands beyond protected areas for biodiversity, and the urgent need to mitigate the impacts of woody plant encroachment on bird biodiversity.

Seed value influences cache pilfering rates by desert rodents.

Some rodents gather and store seeds. How many seeds they gather and how they treat those seeds is largely determined by seed traits such as mass, nutrient content, hardness of the seed coat, presence of secondary compounds, and germination schedule. Through their consumption and dispersal of seeds, rodents act as agents of natural selection on seed traits, and those traits influence how rodents forage. Many seeds that are scatter-hoarded by rodents are pilfered, or stolen, by other rodents, and seed traits also likely influence pilfering rates and seed fates of pilfered seeds. To clarify coevolutionary relationships between rodents and the plants that they disperse, one needs to understand the role of seed traits in rodent foraging decisions. We compared how the seeds of 4 species of plants that are dispersed by scatter-hoarding animals and that differ in value (singleleaf piñon pine, Pinus monophylla; desert peach, Prunus andersonii; antelope bitterbrush, Purshia tridentata; Utah juniper, Juniperus osteosperma) were pilfered and recached by rodents. One hundred artificial caches of the 4 seed species (25 per species) were prepared, and removal by rodents was monitored. Rodents pilfered high-value seeds more rapidly than the other seeds. Desert peach seeds, which contain toxic secondary compounds, were more frequently recached. Relatively low value seeds like Utah juniper and antelope bitterbrush were pilfered more slowly and were sometimes left at cache sites, and seeds of the latter species were transported shorter distances to new cache sites. The background density of seeds also appeared to influence the relative value of seeds.

Faecal mimicry by seeds ensures dispersal by dung beetles.

The large brown, round, strongly scented seeds of Ceratocaryum argenteum (Restionaceae) emit many volatiles found to be present in herbivore dung. These seeds attract dung beetles that roll and bury them. As the seeds are hard and offer no reward to the dung beetles, this is a remarkable example of deception in plant seed dispersal.