Walde, Sandra J.
http://hdl.handle.net/10222/22323
2024-03-28T23:36:14ZNonbreeding-Season Drivers of Population Dynamics in Seasonal Migrants: Conservation Parallels Across Taxa
http://hdl.handle.net/10222/29831
Nonbreeding-Season Drivers of Population Dynamics in Seasonal Migrants: Conservation Parallels Across Taxa
Calvert, Anna M.; Walde, Sandra Joan; Taylor, Philip D.
For seasonal migrants, logistical constraints have often limited conservation efforts to improving survival and reproduction during the breeding season only. Yet, mounting empirical evidence suggests that events occurring throughout the migratory life cycle can critically alter the demography of many migrant species. Herein, we build upon recent syntheses of avian migration research to review the role of non-breeding seasons in determining the population dynamics and fitness of diverse migratory taxa, including salmonid fishes, marine mammals, ungulates, sea turtles, butterflies, and numerous bird groups. We discuss several similarities across these varied migrants: (i) non-breeding survivorship tends to be a strong driver of population growth; (ii) non-breeding events can affect fitness in subsequent seasons through seasonal interactions at individual-and population-levels; (iii) broad-scale climatic influences often alter non-breeding resources and migration timing, and may amplify population impacts through covariation among seasonal vital rates; and (iv) changes to both stationary and migratory non-breeding habitats can have important consequences for abundance and population trends. Finally, we draw on these patterns to recommend that future conservation research for seasonal migrants will benefit from: (1) more explicit recognition of the important parallels among taxonomically diverse migratory animals; (2) an expanded research perspective focused on quantification of all seasonal vital rates and their interactions; and (3) the development of detailed population projection models that account for complexity and uncertainty in migrant population dynamics.
2009-12-01T00:00:00ZPrey Exchange Rates and the Impact of Predators on Prey Populations in Streams
http://hdl.handle.net/10222/29837
Prey Exchange Rates and the Impact of Predators on Prey Populations in Streams
Cooper, S. D.; Walde, Sandra Joan; Peckarsky, B. L.
We present four lines of evidence that the magnitude of prey exchange (=immigration/emigration) among substrate patches has an overwhelming influence on the perceived effects of predators on prey populations. (1) An extensive review of the literature on predation effects in benthic and littoral freshwater habitats revealed a significant relationship between prey exchange rate and observed predator impact. In streams, studies showing significant predator effects used cages with smaller mesh sizes than studies showing nonsignificant effects. Similarly, there was a highly significant correlation between cage mesh size and the magnitude of predator impact on common prey. Large-scale stream studies indicated that prey drift and colonization rate were inversely related to predator impact on benthic prey. (2) These patterns were confirmed by field experiments and observations where mesh size was directly manipulated or where exchange rates varied among taxa. In Colorado streams we saw greater predator impacts on Baetis prey when immigration/emigration was restricted vs. when the mesh size of the cage was relatively large. Similarly, the effects of trout in California stream pools were greater when prey turnover rates were low. (3) A re-analysis of Peckarsky's (1985) data shows an inverse relationship between predator impact and prey mobility within a field experiment. (4) Finally, a model than incorporates both predation and exchange of prey indicates that we ought to expect a lower magnitude of predator effects when exchange rates are high. These results suggest that some discrepancies in past studies may be explained by differences in the exchange rates of prey, and that differences in predator effects across different systems or habitats may be related to variation in the rates of prey dispersal and colonization.
1990-01-01T00:00:00ZSurviving historical Patagonian landscapes and climate: molecular insights from Galaxias maculatus
http://hdl.handle.net/10222/29834
Surviving historical Patagonian landscapes and climate: molecular insights from Galaxias maculatus
Zemlak, Tyler S.; Habit, Evelyn M.; Walde, Sandra Joan; Carrea, Cecilia; Ruzzante, Daniel E.
Background: The dynamic geological and climatic histories of temperate South America have played important roles in shaping the contemporary distributions and genetic diversity of endemic freshwater species. We use mitochondria and nuclear sequence variation to investigate the consequences of mountain barriers and Quaternary glacial cycles for patterns of genetic diversity in the diadromous fish Galaxias maculatus in Patagonia (similar to 300 individuals from 36 locations). Results: Contemporary populations of G. maculatus, east and west of the Andes in Patagonia, represent a single monophyletic lineage comprising several well supported groups. Mantel tests using control region data revealed a strong positive relationship when geographic distance was modeled according to a scenario of marine dispersal. (r = 0.69, P = 0.055). By contrast, direct distance between regions was poorly correlated with genetic distance (r = -0.05, P = 0.463). Hierarchical AMOVAs using mtDNA revealed that pooling samples according to historical (pre-LGM) oceanic drainage (Pacific vs. Atlantic) explained approximately four times more variance than pooling them into present-day drainage (15.6% vs. 3.7%). Further post-hoc AMOVA tests revealed additional genetic structure between populations east and west of the Chilean Coastal Cordillera (coastal vs. interior). Overall female effective population size appears to have remained relatively constant until roughly 0.5 Ma when population size rapidly increased several orders of magnitude [100x (60x-190x)] to reach contemporary levels. Maximum likelihood analysis of nuclear alleles revealed a poorly supported gene tree which was paraphyletic with respect to mitochondrial-defined haplogroups. Conclusions: First diversifying in the central/north-west region of Patagonia, G. maculatus extended its range into Argentina via the southern coastal regions that join the Pacific and Atlantic oceans. More recent gene flow between northern populations involved the most ancient and most derived lineages, and was likely facilitated by drainage reversal(s) during one or more cooling events of the late Pleistocene. Overall female effective population size represents the end result of a widespread and several hundred-fold increase over approximately 0.5 Ma, spanning several climatic fluctuations of the Pleistocene. The minor influence of glacial cycles on the genetic structure and diversity of G. maculatus likely reflects the access to marine refugia during repeated bouts of global cooling. Evidence of genetic structure that was detected on a finer scale between lakes/rivers is most likely the result of both biological attributes (i.e., resident non-migratory behavior and/or landlocking and natal homing in diadromous populations), and the Coastal Cordillera as a dispersal barrier.
2010-03-01T00:00:00ZHow quality of host plant affects a predator-prey interaction in biological control
http://hdl.handle.net/10222/29824
How quality of host plant affects a predator-prey interaction in biological control
Walde, Sandra Joan
In cases of successful biological control the pest population is maintained at low densities by a natural enemy, but the mechanisms by which the predator or parasitoid manages to control the pest are often unknown. This study was undertaken to determine the response of a predator to different population growth rates of its prey within a biological control system. Population growth rate of the phytophagous mite Panonychus ulmi was varied by altering the nutritional status of the host plant (apple trees (Pyrus malus)). NPK fertilizer was added to the soil, resulting in higher nitrogen, lower phosphorus, and lower potassium levels in the foliage of the trees. There appeared to be a nonlinear relationship between nitrogen and P. ulmi densities, with density increasing and then decreasing as nitrogen concentration was increased. Two predaceous mites, Typhlodromus pyri and Zetzellia mali, were implicated in the control of P. ulmi, but the effectiveness of both was reduced at high nitrogen levels. The predators therefore did not fully compensate for increases in the population growth rate of their prey, although P. ulmi densities were maintained well below the economic threshold in all cases. However, the probability of persistence of the prey populations was not significantly affected by the nutrient regimes, suggesting that the fundamental dynamics of the predator-prey interaction were not altered by the range of population growth rates in this study.
1995-01-01T00:00:00Z