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1,445 results for “Distances”

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dryad40/100

Predator exclosures increase nest success but reduce adult survival and increase dispersal distance of Piping Plovers, indicating exclosures should be used with caution

Diagnosing unsuccessful population outcomes for endangered species requires understanding relationships among vital rates, ecological conditions, and management variables, including unintended consequences of management actions. The federally-threatened Piping Plover (Charadrius melodus) has remained below recovery goals, despite intensive management, including the use of nest exclosures to protect eggs from predation. We studied ecological factors and management actions affecting nest success, survival, site fidelity, and dispersal of the New Jersey, USA population of Piping Plovers over a seven-year period, focused on evaluating the impact of exclosures on demography. While exclosures increased nest success by 62% over a 34-day period, exclosed nests were 4.7 times more likely to be abandoned, which was likely a consequence of adult mortality. Abandoned nests were associated with lower adult survival, particularly for males, but there was evidence that site fidelity was greater for birds whose last nest was exclosed vs. unexclosed. Regardless of exclosure status, females who abandoned their first nesting attempt dispersed 10 times farther between attempts than those whose first nest attempts were lost to other causes. Moreover, females that abandoned their last nesting attempts dispersed farther than females that lost their last nest to predation or flooding. This difference was more substantial for males. Our results corroborate studies documenting adverse impacts of exclosures on survival, and, for the first time, demonstrate that surviving mates (particularly females) emigrate from the breeding site, resulting in a realized loss of a local breeding pair. Further, we used an online population project model (i.e., PiperEx) to demonstrate that exclosures are not expected to improve growth rates in New Jersey. We conclude that there is a tradeoff among increased nest survival, reduced adult survival and increased emigration rates, and we encourage managers to consider whether exclosures are worth the protection of eggs from predators using online decision support tools.

opencc-zeroSep 2023View details →

dryad40/100

Urbanization impacts short- but not long-distance natal dispersal in a common orb web spider

Urban environments represent a theatre for life history evolution. Species able to survive in cities can adapt to the local and often divergent environmental conditions compared to rural or (semi-)natural environments. Dispersal determines establishment, gene flow, and thus the potential for local adaptation. Since habitats in urban environments are highly fragmented, and show substantial turnover, contrasting adaptive effects on dispersal are expected. Fragmentation selects against dispersal while patch turn-over is expected to promote the evolution of dispersal. We here show both processes to act in concert when different scales are considered. Dispersal behavior of juvenile, lab-reared garden spiders from three mid-sized European cities were tested under standardized conditions. While long-distance dispersal showed to be overall rare, short-distance dispersal strategies increased with urbanization at small scales, but declined when urbanization was quantified at large scales. We discuss the putative drivers behind these differences in natal dispersal and highlight its importance for urban evolution and ecology.

opencc-zeroSep 2023View details →

dryad40/100

The irreplaceable role of surviving megafauna in long-distance seed dispersal: Evidence from an experiment with Neotropical mammals

The downsizing of disperser assemblages by selective defaunation is a worldwide phenomenon thought to have important consequences in animal-dispersed plants. Numerous large-seeded Neotropical plants currently depend on the last megafaunal survivors, the large tapirs Tapirus spp., and medium-sized frugivores. The extent to which medium frugivores are functionally equivalent to tapirs remains unresolved. We combined feeding trials, seed dispersal kernel modeling based on seed retention times and animal movement simulation (Levy walks), and germination experiments in a large-seeded palm to assess the dispersal quality provided by the largest (tapirs) and two medium (foxes and howler monkeys) frugivore species in terms of dispersal distances and gut passage effects on germination. Tapirs retained the seeds in the gut for much longer (mean=221 hours) than howlers (43 h) and foxes (22 h). Median dispersal distance by tapirs (1252 m) was 14 and 40 times larger than that by foxes (88 m) and howlers (31 m), respectively. The seed dispersal kernel of tapirs showed a 5th percentile value (291 m) larger than the 95th percentiles of foxes (285 m) and howlers (108 m). Manually depulped and gut-passed seeds germinated in similar proportions, showing, respectively, 3.5 and 2.5―2.9 times higher values than intact fruits. Germination probability and seed viability decreased with retention time in howlers' and tapirs' gut, with howlers showing a steeper negative relationship. Such detrimental effect implies a trade-off between germination success and dispersal distance. We conclude that tapirs may not play a unique role in germination enhancement but move seeds much further than medium frugivores, thus playing a critical role as long-distance dispersers of many plants. This study provides important insights on palm–frugivore interactions and the potential consequences for large-seeded plants of losing the last megafaunal representatives in the Neotropics.

opencc-zeroMay 2024View details →

dryad40/100