Keystone predation can be a determinant of community structure, including species diversity, but factors underlying “keystoneness” have been minimally explored. Using the system in which the original keystone, the sea star
Alternate attractors have been shown to exist in a variety of terrestrial and aquatic systems,
- NSF-PAR ID:
- 10246838
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Marine Ecology
- Volume:
- 37
- Issue:
- 6
- ISSN:
- 0173-9565
- Page Range / eLocation ID:
- p. 1179-1189
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract Pisaster ochraceus , was discovered, we focused on two potential (but overlapping) determinants of keystoneness: intrinsic traits or state variables of the species (e.g., size, density), and extrinsic environmental parameters (e.g., prey productivity) that may provide conditions favorable for keystone predator evolution. Using a comparative‐experimental approach, with repeated field experiments at multiple sites across a variable coastal environment, we tested predation rates, or how quickly predators consumed prey, and predation effects, or community response to predator presence or absence. We tested five hypotheses: (H 1) predation rates and effects will vary in space but not time; (H 2) per population predation rates will vary primarily with individual traits and population variables; (HJHH3) per capita predation rates will vary only with individual traits; (H 4) predation effects will vary with traits, variables, and external drivers; and (H 5) as predicted by the keystone predation hypothesis, diversity will vary unimodally with predation pressure. As hypothesized, predation rates differed among sites but not over time (H 1), and in caging exclusion experiments, predation effect varied with both intrinsic and extrinsic factors (H 4). Unexpectedly, predation rates varied with both intrinsic and extrinsic (H 2, per population), or only with extrinsic (H 3, per capita) factors. Further, in large‐plot exclusion experiments, predation effect was most closely associated with individual traits (contraH 4). Finally, taxon diversity varied unimodally with proxies of predation pressure (sessile prey abundance) and was sensitive to extrinsic factors (mussel growth, temperature, and upwelling,H 5). Hence, keystoneness depended on predator individual traits, predator population variables, and environmental parameters. However, temporal differences in caging experiments suggested that environmental characteristics underlying prey dynamics may be preeminent. Compared to prior experiments, predation was weaker with low prey input compared to periods with high prey input. Collectively, our results suggest that keystone predator evolution depends on the coalescence of species‐specific characteristics, and environmental parameters favoring high prey productivity. Our approach may be a model for future studies exploring the generality of keystoneness. -
null (Ed.)Shifts between the alternate stable states of sea urchin barren grounds and kelp forests correspond to sea urchin density. In the Aleutian Archipelago, green sea urchins Strongylocentrotus polyacanthus are the dominant herbivores that graze kelp forests. Sea urchin recruitment is an important driver that influences sea urchin density, particularly in the absence of top-down control from a keystone predator such as the sea otter Enhydra lutris . To understand how the biological community may influence patterns of sea urchin recruitment, we compared sea urchin recruit (size ≤20 mm) densities with biomass of other benthic organisms in both barren ground and kelp forest habitats at 9 islands across the Aleutian Archipelago. Patterns of biological community structure between the 2 habitats did not explain patterns of sea urchin recruits; however, the same 10 specific taxa were found to correlate with sea urchin recruits in each habitat. Taxa that showed strong positive correlations included Codium, Constantinea, Schizymenia, and hydrozoans, while strong negative correlations were observed with Pachyarthron and Pugettia . Weak positive correlations were observed with Alcyonidium and ascidiaceans in both habitats, while weak variable relationships were detected with Polysiphonia and Corallina between habitats. The observed species-specific relationships may be due to small sea urchin displacement by larger conspecifics, larval responses to settlement cues, post-settlement survival via biogenic refugia, or potentially predation. These potential species-specific interactions were apparent, regardless of habitat, and it can be inferred that they would be preserved in the presence or absence of keystone predation.more » « less
-
more » « less
Abstract Giant clams (subfamily: Tridacninae) are an important food and economic resource for the Republic of Palau and the greater Indo‐Pacific region. However, giant clam diversity and distribution data for Palau are out of date.
This study reports the species diversity and distribution of giant clams across the Palauan archipelago (total survey area of 3,3002m) from data collected between 2015–2017.
This is the first documented finding of
Tridacna noae in Palau, however, it was rare. Only four individuals were found at only two locations.Results show that Palau is home to a diverse and abundant population of giant clams.
Tridacna crocea (an important food and economic resource) exhibited the highest abundance, with an average of 20.0 ± 2.9 individuals per 50 m2.Tridacna maxima andTridacna squamosa were ranked next in abundance. In contrast,T. noae ,Tridacna derasa ,Tridacna gigas , andHippopus hippopus were found in low numbers or only found in few locations.The density of all recruits, juveniles, and adult
T. crocea T. maxima T. crocea Taken as a whole, clam populations in Palau remain reasonably abundant and healthy. As demand for giant clams continues to rise in Palau and the region, local regulations should focus on sustainable fishing practices by establishing size limits, species bans, and long‐term monitoring plans to maintain the diverse populations of giant clams found there.
-
more » « less
Abstract Selective logging is the primary cause of tropical forest degradation and is rapidly expanding worldwide. While the impacts of logging on species diversity and distributions are well understood, little is known about the effects of logging on animal behaviours central to individual fitness and population persistence.
The song rate of breeding songbirds is a behavioural trait that is often positively associated with male density and used by conspecific females as an indicator of territory and male quality. Thus, contrasting logging‐induced adjustments in song rates of individual birds with population shifts may illuminate potential mechanisms underlying population distributions.
We present a novel application of bioacoustic monitoring, integrating counts of individuals, songs and duets from single automated recording units (ARUs) with
N ‐mixture models, to estimate shifts in population parameters (occupancy, abundance) and singing behaviours (per‐capita song rates, per‐pair duet rates) of 32 Bornean songbird species with logging. We tested hypotheses on the relationships between adjustments in behavioural and population parameters with logging, and further tested the extent to which species traits predicted behavioural and population shifts.Adjustments to singing behaviour in 59 and 53% of species (57% of duetting species) were concordant with differences in occupancy and abundance respectively, such that species showing reduced populations with logging also produced fewer songs per‐capita, and vice versa. Species known to prefer undisturbed habitats and large‐bodied species showed the most negative effects of logging on singing behaviour and population distributions. Species known to exploit degraded habitats exhibited the opposite pattern. Subdued singing in logged forests by species of conservation concern suggests limited competition between territorial males in small populations and may also signal low‐quality territories.
Synthesis and applications . We demonstrate that bioacoustic monitoring can be used to not only estimate important population parameters of occupancy and abundance across a diverse tropical songbird community, but also enables quantification of behaviours considered relevant to individual fitness, yet unobtainable with conventional methods (e.g. point counts). Bioacoustics provides a viable approach to reliable automated large‐scale monitoring of hyperdiverse tropical forest systems under logging operations and other land‐use pressures. -
more » « less
Abstract Insect–pathogen dynamics can show seasonal and inter‐annual variations that covary with fluctuations in insect abundance and climate. Long‐term analyses are especially needed to track parasite dynamics in migratory insects, in part because their vast habitat ranges and high mobility might dampen local effects of density and climate on infection prevalence.
Monarch butterflies
Danaus plexippus are commonly infected with the protozoanOphryocystis elektroscirrha (OE ). Because this parasite lowers monarch survival and flight performance, and because migratory monarchs have experienced declines in recent decades, it is important to understand the patterns and drivers of infection.Here we compiled data on
OE infection spanning 50 years, from wild monarchs sampled in the United States, Canada and Mexico during summer breeding, fall migrating and overwintering periods. We examined eastern versus western North American monarchs separately, to ask how abundance estimates, resource availability, climate and breeding season length impact infection trends. We further assessed the intensity of migratory culling, which occurs when infected individuals are removed from the population during migration.Average infection prevalence was four times higher in western compared to eastern subpopulations. In eastern North America, the proportion of infected monarchs increased threefold since the mid‐2000s. In the western region, the proportion of infected monarchs declined sharply from 2000 to 2015, and increased thereafter. For both eastern and western subpopulations, years with greater summer adult abundance predicted greater infection prevalence, indicating that transmission increases with host breeding density. Environmental variables (temperature and NDVI) were not associated with changes in the proportion of infected adults. We found evidence for migratory culling of infected butterflies, based on declines in parasitism during fall migration. We estimated that tens of millions fewer monarchs reach overwintering sites in Mexico as a result of
OE , highlighting the need to consider the parasite as a potential threat to the monarch population.Increases in infection among eastern North American monarchs post‐2002 suggest that changes to the host’s ecology or environment have intensified parasite transmission. Further work is needed to examine the degree to which human practices, such as mass caterpillar rearing and the widespread planting of exotic milkweed, have contributed to this trend.
