Dreissenid mussels (including the zebra mussel
We used a 27‐year record of Long‐term trends include the 2008 appearance of the quagga mussel ( We observed persistent, strong cycles in adult abundance and body size. These were driven by the appearance and decay of eight dominant year classes over the 27 years of our study, and were a result of temporal variation in recruitment rather than temporal variation in survivorship. The observed strongly irregular recruitment appears to arise from strong adult–larval interactions, and is consistent with previous simulation model results showing that interactions between adults and larvae can drive persistent cycling. We found evidence that negative density dependence affects recruitment, somatic growth, and body condition of We put our results into the context of a conceptual model of
- NSF-PAR ID:
- 10458710
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Freshwater Biology
- Volume:
- 65
- Issue:
- 3
- ISSN:
- 0046-5070
- Page Range / eLocation ID:
- p. 474-489
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract Dreissena polymorpha and the quagga musselD. rostriformis ) are among the world's most notorious invasive species, with large and widespread ecological and economic effects. However, their long‐term population dynamics are poorly known, even though these dynamics are critical to determining impacts and effective management. We gathered and analyzed 67 long‐term (>10 yr) data sets on dreissenid populations from lakes and rivers across Europe and North America. We addressed five questions: (1) How doDreissena populations change through time? (2) Specifically, doDreissena populations decline substantially after an initial outbreak phase? (3) Do different measures of population performance (biomass or density of settled animals, veliger density, recruitment of young) follow the same patterns through time? (4) How do the numbers or biomass of zebra mussels or of both species combined change after the quagga mussel arrives? (5) How does body size change over time? We also considered whether current data on long‐term dynamics ofDreissena populations are adequate for science and management. IndividualDreissena populations showed a wide range of temporal dynamics, but we could detect only two general patterns that applied across many populations: (1) Populations of both species increased rapidly in the first 1–2 yr after appearance, and (2) quagga mussels appeared later than zebra mussels and usually quickly caused large declines in zebra mussel populations. We found little evidence that combinedDreissena populations declined over the long term. Different measures of population performance were not congruent; the temporal dynamics of one life stage or population attribute cannot generally be accurately inferred from the dynamics of another. We found no consistent patterns in the long‐term dynamics of body size. The long‐term dynamics ofDreissena populations probably are driven by the ecological characteristics (e.g., predation, nutrient inputs, water temperature) and their temporal changes at individual sites rather than following a generalized time course that applies across many sites. Existing long‐term data sets on dreissenid populations, although clearly valuable, are inadequate to meet research and management needs. Data sets could be improved by standardizing sampling designs and methods, routinely collecting more variables, and increasing support. -
more » « less
<italic>Abstract</italic> Non‐native species are among the most important drivers of the structure and function of modern ecosystems. The ecological impacts of a non‐native species ought to depend on the size and characteristics of its population, but the exact nature of this population‐impacts relationship is rarely defined. Both the mathematical form of this relationship (e.g., linear, exponential, and threshold) and the attributes of the invading population (e.g., density, biomass, and body size) that most efficiently describe its impacts could vary greatly across invaders, ecosystems, and ecological variables. Knowing the shape of this relationship could improve management and help to infer mechanisms of interaction between the invader and ecosystem. We used a long‐term data set on the invasion of the Hudson River ecosystem by two species of
Dreissena (the zebra mussel,Dreissena polymorpha , and the quagga mussel,Dreissena rostriformis ) to explore the shape of the population‐impacts relationship for selected ecological variables, including seston, phytoplankton, and several taxa of zooplankton. Most population‐impacts relationships appeared to follow a negative exponential form, but we also found apparent thresholds and scatterplots for some variables. Including information on the traits ofDreissena (body size and filtration rate) often substantially improved models of impacts. We found only slight evidence that the resistance of the Hudson River ecosystem to theDreissena invasion might be increasing over time. Our results suggest important refinements to widely used conceptual models of invasive species impact, and indicate that defining the population‐effects relationship will be essential in understanding and managing the impacts of non‐native species. -
more » « less
Abstract The evolution of seed size may be influenced by intrinsic attributes of populations, such as mating system and extrinsic factors, such as climate. Several hypotheses propose that the evolution of self‐fertilization from an outcrossing progenitor will be accompanied by a reduction in seed size, but this prediction has not been rigorously tested. Many studies report that the mean seed size of populations or taxa is associated with long‐term climate conditions. Here, we examined the effects on seed size of both mating system and climate within a single genus.
In the California wildflower genus,
Clarkia (Onagraceae), we sampled seeds from 58 populations representing three pairs of sister taxa; each pair included a predominantly outcrossing and a facultatively selfing taxon. We then examined the independent effects on population mean seed size of mating system, elevation, long‐term (30‐year) climate conditions, and climate anomalies (the deviation between conditions in the year of collection and the long‐term mean), focusing on maximum monthly temperature (T max), cumulative moisture deficit and cumulative precipitation (PPT) duringClarkia's growing season (fall, winter and spring).In each taxon pair, the selfing taxon had smaller seeds than the outcrosser. Local, long‐term (1921–1980 and 1981–2000) mean
T max, PPT and elevation were independently and negatively associated with seed size. Long‐term means forT maxand PPT explain geographical variation in seed size better than climate anomalies in the year of collection.Synthesis . We corroborated two key hypotheses concerning the drivers of geographical variation in mean seed size. Small seeds inClarkia co‐evolve with selfing (although the mechanism remains elusive) and in response to chronically warm and wet conditions. The effect of long‐term mean precipitation on seed size differs qualitatively from the effect of precipitation anomalies; relatively large seeds are produced in populations experiencing wetter‐than‐normal years. Ongoing climate change may therefore generate conflicting selection on seed size inClarkia : intensifying drought is likely to lead to an evolutionary increase in seed size due to its effects on seedling survivorship, while climate‐driven declines in pollinators or selection favouring more rapid reproduction may promote the evolution of self‐pollination, facilitating the evolution of smaller seeds. -
more » « less
Abstract Body size influences an individual's physiology and the nature of its intra‐ and interspecific interactions. Changes in this key functional trait can therefore have important implications for populations as well. For example, among invertebrates, there is typically a positive correlation between female body size and reproductive output. Increasing body size can consequently trigger changes in population density, population structure (e.g. adult to juvenile ratio) and the strength of intraspecific competition.
Body size changes have been documented in several species in the Arctic, a region that is warming rapidly. In particular, wolf spiders, one of the most abundant arctic invertebrate predators, are becoming larger and therefore more fecund. Whether these changes are affecting their populations and role within food webs is currently unclear.
We investigated the population structure and feeding ecology of the dominant wolf spider species
Pardosa lapponica at two tundra sites where adult spiders naturally differ in mean body size. Additionally, we performed a mesocosm experiment to investigate how variation in wolf spider density, which is likely to change as a function of body size, influences feeding ecology and its sensitivity to warming.We found that juvenile abundance is negatively associated with female size and that wolf spiders occupied higher trophic positions where adult females were larger. Because female body size is positively related to fecundity in
P. lapponica , the unexpected finding of fewer juveniles with larger females suggests an increase in density‐dependent cannibalism as a result of increased intraspecific competition for resources. Higher rates of density‐dependent cannibalism are further supported by the results from our mesocosm experiment, in which individuals occupied higher trophic positions in plots with higher wolf spider densities. We observed no changes in wolf spider feeding ecology in association with short‐term experimental warming.Our results suggest that body size variation in wolf spiders is associated with variation in intraspecific competition, feeding ecology and population structure. Given the widespread distribution of wolf spiders in arctic ecosystems, body size shifts in these predators as a result of climate change could have implications for lower trophic levels and for ecosystem functioning.
-
more » « less
Abstract Aim Climate‐induced pulse (e.g., hurricanes) and press (e.g., global warming) disturbances represent threats to populations, communities, and the ecosystem services that they provide. We leveraged three decades of annual data on tropical gastropods to quantify the effects of major hurricanes, associated secondary succession, and global warming on abundance, biodiversity, and species composition.
Location Luquillo Mountains, Puerto Rico.
Methods Gastropod abundance, biodiversity, and composition were estimated annually for each of 27 years in a tropical montane forest that experienced three major hurricanes (Hugo, Georges, and Maria). Generalized linear mixed‐effects, linear mixed‐effects, and linear models evaluated population‐ and community‐level responses to year, ambient temperature, understorey temperature, hurricane, and time since hurricane. Variation partitioning determined the unique and shared variation in biotic responses associated with temperature, disturbance, and succession.
Results Rather than declining, gastropod abundances generally increased through time, whereas the responses of biodiversity were weak and scale dependent. Hurricanes and associated secondary succession, rather than ambient atmospheric temperature, moulded long‐term trends in abundances and biodiversity.
Main conclusions Global warming over the past 30 years has not progressed sufficiently to elicit significant responses by gastropods in the Luquillo Mountains. Rather, effects from pulse disturbances (i.e., hurricanes) and secondary succession currently drive long‐term variation in abundance and biodiversity. Gastropods evince high resilience in this tropical ecosystem. Historical exposure to recurrent hurricanes likely imbued the fauna with broad niches that make them resistant to current levels of global warming. We predict that biotic resiliency will be challenged once changes in temperature exceed interannual and inter‐habitat differences that typify this hurricane‐mediated system, or combine with an increased frequency of hurricanes and droughts to alter associations among environmental characteristics that define the fundamental niches of species. Only then might significant declines in abundance or the appearance of novel communities characterize the gastropod fauna in the Luquillo Mountains.
