Month: September 2022

UNFINISHED TREND. “Today, the number of house sparrows in North America is only some 25 million, and the trend continues downward.” https://link.springer.com/chapter/10.1007/978-3-319-55396-2_5 View in LinkedIn

INDIAN SPARROW COLLAPSE. “In recent years India also has seen a dramatic decline of sparrow populations. In recent years, ornithologists have observed sharp decline in house sparrow populations across Bangalore, Mumbai, Hyderabad and other cities in India.” https://lnkd.in/e6evZ-H View in LinkedIn

IMPACT OF COLONY COLLAPSE. “It has been observed widely that the local abundance and regional distribution of species tend to be correlated positively, such that species with low abundance within sites (i.e. average numbers or densities of individuals) also tend to occupy few sites (i.e. the area or range of a species at a national or continental scale), while species with high abundance also tend to occupy a large number of sites.” https://lnkd.in/dZAJ-iq View in LinkedIn

THE ALLEE EFFECT, popularized in the memorable book, The Moth Snowstorm by Michael McCarthy describes how social bird colonies like sparrows will collapse when the population falls below a certain threshold, and has contributed to the drastic loss of sparrow populations. https://lnkd.in/dp2SYmj View in LinkedIn

SO ENDS this vignette on the once common sparrow and its demise in numerous cultures. Between being human-dependent, and having a critical threshold for colony size, the sparrow collapse has suffered from these two factors. What is most dramatic is how such a common bird can collapse so quickly in so many places. It surely is a canary for mankind. View in LinkedIn

RESOURCE BUDGETS. “Investment into reproduction – or early fitness components in general – might withdraw limited resources that could otherwise be used for somatic maintenance and repair. Such resource allocation trade-offs can thus been seen as a physiological extension of Williams' AP model.” http://www.nature.com/scitable/knowledge/library/the-evolution-of-aging-23651151 View in LinkedIn

TWO AGING MODELS. “The classical evolutionary theory of aging has therefore two fundamental cornerstones: MA and AP. However, it is worth noting that both models are conceptually very similar: under MA, aging evolves through the accumulation of effectively neutral mutations with deleterious late-life effects, whereas, under AP, aging occurs due to mutations with beneficial early- and deleterious late-life effects. In reality, probably both types of mutations occur in populations, yet their relative frequencies remain unknown.” http://www.nature.com/scitable/knowledge/library/the-evolution-of-aging-23651151 View in LinkedIn

RANGE OF LONGEVITY. “Different species vary dramatically in how long they life. The dome-shelled Galápagos giant tortoise (Geochelone elephantopus) can reach an age of about 180 years, whereas some mayfly species (belonging to the insect order Ephemeroptera) die after about 30 minutes. Even older than giant tortoises are certain trees, such as the yew (Taxus baccata), with some specimens between 4,000 and 5,000 years old. A few other organisms, such as freshwater polyps of the genus Hydra, are thought to age at a negligible rate or to be even potentially immortal, although this is still somewhat controversial.” http://www.nature.com/scitable/knowledge/library/the-evolution-of-aging-23651151 View in LinkedIn

LIFESPAN AND BREEDING. “A longer lifespan normally implies increased reproductive success, and factors such as low adult mortality (permitting more reproductive events per lifetime), high juvenile mortality (making it necessary for adults to reproductively compensate for such loss), and high variation in juvenile mortality from one bout of reproduction to the next (increasing uncertainty in reproductive success and requiring reproductive compensation as well) therefore all tend to lengthen reproductive lifespan.” http://www.nature.com/scitable/knowledge/library/the-evolution-of-aging-23651151 View in LinkedIn

THE EQUATION. “These lifespan promoting effects of selection are balanced by those that tend to increase adult mortality relative to juvenile mortality. Consequently, if extrinsic, environmentally imposed adult mortality is high, selection becomes weak, thereby allowing the evolution of higher levels of intrinsic mortality (i.e., aging).” http://www.nature.com/scitable/knowledge/library/the-evolution-of-aging-23651151 View in LinkedIn