Long-distance dispersal of aquatic invertebrates by ducks increases with propagule size

 

Migratory ducks are key dispersal agents for aquatic organisms. Some groups are, however, particularly understudied. Despite consistent evidence of the potential  role of waterbird-mediated dispersal for aquatic invertebrates, and the key role of this group in the functioning of aquatic ecosystems, most evidencece remains anecdotal - or it is restricted to the collection of viable propagule in waterbird faces collected in the wild

In the article 'Evidence that long-distance dispersal of aquatic invertebrates by ducks increases with propagule size', which got published yesterday in Freswater Biology, researchers from the Doñana Biological Station and the Netherlands Institute of Ecology (NIOO-KNAW) teamed up to explore the potential for short- and long-distance dispersal of aquatic invertebrates, using a combinsation of experimental evidence and process-based modelling .

Using seven species of aquatic invertebrates and a duck species known to feed on them in the wild (the northern shoveler) as a model system, we evaluated whether their potential for endozoochorous dispersal varies among species, and the role of propagule size and morphology (e.g., the number of protective layers) in explaining such variation.  We also tested the expectation of a lower dispersal potential for invertebrate propagules, as compared to plant seeds; and evaluated whether intra-specific variation (in particular, sexual dimorphism) influences the potential of waterbirds as dispersal vectors.

Results showed that endozoochory of invertebrate propagules by waterbirds results in frequent dispersal among wetlands (tens of km) and regular dispersal at regional scale (over a hundred km). Increasing propagule size had two contrasting effects on invertebrate dispersal potential, decreasing the frequency of dispersal (fewer seeds dispersed) but increasing the potential for long-distance dispersal.

Habitat heterogeneity increases wild ungulate resilience to climatic variation

 

Mediterranean environments are characterized by strong fluctuations in plant primary production. These fluctuations can regulate the carrying capacity of ungulate populations, but their effects may vary across spatial and temporal scales. In particular, habitat heterogeneity may allow wild ungulates to mitigate temporal fluctuations in plant production by using different resources along the year. 

In the article Landscape heterogeneity increases the stability of wild ungulate populations facing climatic variability in Mediterranean ecosystems, published last week in STOTEN, J.M. Giralt and L. Santamaría use a 15-years dataset (including remote-sensing data and ungulate population counts) to assess how temporal variability in plant primary production and livestock abundance influence the population dynamics of two wild ungulates: native red deer and introduced fallow deer. 

Results show that temporal alternation in the phenology of the four different vegetation types increased  food availability for ungulates within each year; and  complementarity in the responses of different vegetation types  increased the predictability of food availability across different years.

Domestic ungulates had positive effects on wild ungulate density at low to intermediate abundances, but high livestock densities decreased ungulate density and constrained the stability of the plant-ungulate system in response to the impact of climatic variation, particularly under climate change.