Species abundance distributions (SADs) follow one of ecology's oldest and most universal laws - every community shows a hollow curve or hyperbolic shape on a histogram with many rare species and just ...a few common species. Here, we review theoretical, empirical and statistical developments in the study of SADs. Several key points emerge. (i) Literally dozens of models have been proposed to explain the hollow curve. Unfortunately, very few models are ever rejected, primarily because few theories make any predictions beyond the hollow-curve SAD itself. (ii) Interesting work has been performed both empirically and theoretically, which goes beyond the hollow-curve prediction to provide a rich variety of information about how SADs behave. These include the study of SADs along environmental gradients and theories that integrate SADs with other biodiversity patterns. Central to this body of work is an effort to move beyond treating the SAD in isolation and to integrate the SAD into its ecological context to enable making many predictions. (iii) Moving forward will entail understanding how sampling and scale affect SADs and developing statistical tools for describing and comparing SADs. We are optimistic that SADs can provide significant insights into basic and applied ecological science.
Empirical evaluation of neutral theory McGill, Brian J.; Maurer, Brian A.; Weiser, Michael D.
Ecology (Durham),
June 2006, Volume:
87, Issue:
6
Journal Article
Peer reviewed
We describe a general framework for testing neutral theory. We summarize similarities and differences between ten different versions of neutral theory. Two central predictions of neutral theory are ...that species abundance distributions will follow a zero-sum multinomial distribution and that community composition will change over space due to dispersal limitation. We review all published empirical tests of neutral theory. With the exception of one type of test, all tests fail to support neutral theory. We identify and perform several new tests. Specifically, we develop a set of best practices for testing the fit of the zero-sum multinomial (ZSM) vs. a lognormal null hypothesis and apply this to a data set, concluding that the lognormal outperforms neutral theory on robust tests. We explore whether a priori parameterization of neutral theory is possible, and we conclude that it is not. We show that non-curve-fitting predictions readily derived from neutral theory are easily falsifiable. In toto, there is a current overwhelming weight of evidence against neutral theory. We suggest some next steps for neutral theory.
In three studies (N = 854), including one pre‐registered study, we examined factors that might influence American parents’ decisions to side with owners versus promote prosociality or sharing when ...thinking about children's property conflicts. We found that parents’ thinking about property conflicts was affected by the relationships among the parents and their children. Namely, parents were most likely to side with owners when their child was described as transgressing upon another's property. Conversely, when the parents’ child was the owner, they were more likely to encourage sharing. Parents’ explanations revealed that their decisions were a reflection of their personal beliefs about the importance of personal rights and/or promoting prosociality. The findings also suggested that some parents were reasoning in nuanced ways about the importance of teaching children about consent and its link to ownership. The findings from these studies have bearing on the potential role of parental input in young children's appreciation of owners’ rights. These results suggest that parents may be providing children with some informative input regarding the nature of ownership rights such as when they matter most.
Understanding the factors that influence the presence and distribution of carnivores in human-dominated agricultural landscapes is one of the main challenges for biodiversity conservation, especially ...in landscapes where setting aside large protected areas is not feasible. Habitat use models of carnivore communities in rubber plantations are lacking despite the critical roles carnivores play in structuring ecosystems and the increasing expansion of rubber plantations. We investigated the habitat use of a mammalian carnivore community within a 4,200-ha rubber plantation/forest landscape in Bahia, Brazil. We placed two different brands of camera traps in a 90-site grid. We used a multispecies occupancy model to determine the probabilities of habitat use by each species and the effect of different brands of camera traps on their detection probabilities. Species showed significant differences in habitat use with domestic dogs (Canis familiaris) and crab-eating foxes (Cerdocyon thous) having higher probabilities of using rubber groves and coatis (Nasua nasua) having a higher probability of using forest. The moderate level of captures and low detection probabilities (≤ 0.1) of tayras (Eira barbara) and wildcats (Leopardus spp.) precluded a precise estimation of habitat use probabilities using the multispecies occupancy model. The different brands of camera traps had a significant effect on the detection probability of all species. Given that the carnivore community has persisted in this 70-year-old landscape, the results show the potential of rubber/forest landscapes to provide for the long-term conservation of carnivore communities in the Atlantic forest, especially in mosaics with 30-40% forest cover and guard patrolling systems. The results also provide insights for mitigating the impact of rubber production on biodiversity.
This exploratory report investigates how children, aged 6‐ to 12‐years, reason about divisions in labour. It focuses on understanding when in development children might associate higher status groups ...with intellectual as opposed to physical labour. It explores this question by introducing a sample of mostly mid/high‐SES American children to a novel factory setting and then asking them who is likely to have one of two jobs: a ‘builder’ (physical labour), or ‘thinker’ (intellectual labour) job. Older children were more likely than younger children to associate an individual's higher social status with intellectual labour work as opposed to physical labour work. Children also explained their reasoning, and with age their explanations focused more on social factors like the role of access to ‘choices’ or opportunities in shaping the nature of others' work.
Polymicrobial bronchopulmonary infections in cystic fibrosis (CF) cause progressive lung damage and death. Although the arrival of Pseudomonas aeruginosa often heralds a more rapid rate of pulmonary ...decline, there is significant inter-individual variation in the rate of decline, the causes of which remain poorly understood. By coupling culture-independent methods with ecological analyses, we discovered correlations between bacterial community profiles and clinical disease markers in respiratory tracts of 45 children with CF. Bacterial community complexity was inversely correlated with patient age, presence of P. aeruginosa and antibiotic exposure, and was related to CF genotype. Strikingly, bacterial communities lacking P. aeruginosa were much more similar to each other than were those containing P. aeruginosa, regardless of antibiotic exposure. This suggests that community composition might be a better predictor of disease progression than the presence of P. aeruginosa alone and deserves further study.
The range of potential mechanisms limiting species' distributions in space is nearly as varied and complex as the diversity of life itself. Yet viewed abstractly, a species' border is a geographic ...manifestation of a species' demographic responses to a spatially and temporally varying world. Population dynamic models provide insight into the different routes by which range limits can arise owing to gradients in demographic rates. In a metapopulation context, for example, range limits may be caused by gradients in extinction rates, colonization rates or habitat availability. We have consider invasion models in uniform and heterogeneous environments as a framework for understanding non-equilibrium range limits, and explore conditions under which invasions may cease to spread leaving behind a stationary range limit. We conclude that non-equilibrial range dynamics need further theoretical and empirical attention.
One of the longest running debates in ecology is whether chance or determinism structures biotic communities, and this question is often studied by looking for the presence or absence of community ...inertia (lack of change) over time or space. Results have been equivocal. We adopted three tactics for a fresh approach: (i) allowing the answer to vary with the geographic, temporal, and taxonomic scale of study, (ii) using appropriate reference points for the amount of inertia in random biological systems, and (iii) using a robust approach for measurement of inertia. We examined fossil assemblages of mammalian communities across almost 1,000,000 years and at sites spanning ≈3,500 km. We showed that in general there is good evidence for inertia but that the results change in a quantifiable fashion with taxonomic, spatial, and temporal scales. By using neutral theory we place a reference point on the degree of inertia and demonstrate that empirical mammalian communities show greater inertia than neutral communities over time scales >3,000 year. Although our results do not specifically reveal mechanism, they emphasize that deterministic forces are at work in structuring communities over millennia.
The species abundance distribution (SAD) is one of the few universal patterns in ecology. Research on this fundamental distribution has primarily focused on the study of numerical counts, ...irrespective of the traits of individuals. Here we show that considering a set of Generalized Species Abundance Distributions (GSADs) encompassing several abundance measures, such as numerical abundance, biomass and resource use, can provide novel insights into the structure of ecological communities and the forces that organize them. We use a taxonomically diverse combination of macroecological data sets to investigate the similarities and differences between GSADs. We then use probability theory to explore, under parsimonious assumptions, theoretical linkages among them. Our study suggests that examining different GSADs simultaneously in natural systems may help with assessing determinants of community structure. Broadening SADs to encompass multiple abundance measures opens novel perspectives in biodiversity research and warrants future empirical and theoretical developments.
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