The relationship between the energy expended per offspring, fitness of offspring, and parental fitness is presented in a two-dimensional graphical model. The validity of the model in determining an optimal parental strategy is demonstrated analytically. The model applies under various conditions of parental care and sibling care for the offspring but is most useful for species that produce numerous small offspring which are given no parental care.

The Optimal Balance between Size and Number of Offspring

The rate of reproduction, age at maturity and longevity vary widely among species. Most of this life-history variation falls on a slow-fast continuum, with low reproductive rate, slow development and long life span at one end and the opposite traits at the other end. The absence of alternative combinations of these variables implies constraint on the diversification of life histories, but the nature of this constraint remains elusive. Here, we argue that individual and adaptive responses to different environments are limited by physiological mechanisms. Although energy and materials allocations are important results of physiological tradeoffs, endocrine control mechanisms can produce incompatible physiological states that restrict life histories to a single dominant axis of variation. To approach the problem of life-history variation properly, studies should integrate behavior and physiology within the environmental and demographic contexts of selection.

/pdf/the-physiology-life-history-nexus-59kntuzzij.pdf

The physiology/life-history nexus

Summary

1
Demographic data from both breeding and non-breeding periods are needed to manage populations of migratory birds, many of which are declining in abundance and are of conservation concern. Although habitat associations, and to a lesser extent, reproductive biology, are known for many migratory species, few studies have measured survival rates of these birds at different parts of their annual cycle.

2
Cormack–Jolly–Seber models and Akaike’s information criterion model selection were used to investigate seasonal variation in survival of a Nearctic – Neotropical migrant songbird, the black-throated blue warbler, Dendroica caerulescens. Seasonal and annual survival were estimated from resightings of colour-ringed individuals on breeding grounds in New Hampshire, USA from 1986 to 2000 and on winter quarters in Jamaica, West Indies from 1986 to 1999. Warblers were studied each year during the May–August breeding period in New Hampshire and during the October–March overwinter period in Jamaica.

3
In New Hampshire, males had higher annual survival (0·51 ± 0·03) and recapture probabilities (0·93 ± 0·03) than did females (survival: 0·40 ± 0·04; recapture: 0·87 ± 0·06). In Jamaica, annual survival (0·43 ± 0·03) and recapture (0·95 ± 0·04) probabilities did not differ between sexes. Annual survival and recapture probabilities of young birds (i.e. yearlings in New Hampshire and hatch-year birds in Jamaica) did not differ from adults, indicating that from the time hatch-year individuals acquire territories on winter quarters in mid-October, they survive as well as adults within the same habitat.

4
Monthly survival probabilities during the summer (May–August) and winter (October–March) stationary periods were high: 1·0 for males in New Hampshire, and 0·99 ± 0·01 for males in Jamaica and for females in both locations.

5
These annual and seasonal survival estimates were used to calculate warbler survival for the migratory periods. Monthly survival probability during migration ranged from 0·77 to 0·81 ± 0·02. Thus, apparent mortality rates were at least 15 times higher during migration compared to that in the stationary periods, and more than 85% of apparent annual mortality of D. caerulescens occurred during migration.

6
Additional data from multiple species, especially measures of habitat-specific demography and dispersal, will improve our understanding of the relative impacts of the breeding, migratory, and winter periods on population dynamics of migratory birds and thus enhance future conservation efforts.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2656.2002.00599.x

Variation in survivorship of a migratory songbird throughout its annual cycle

Summary
Parameters used to characterize the course of growth are described, and calculated growth parameters are presented for 105 species of birds of many taxonomic groups from a wide range of geographical localities.

Growth parameters are found to exhibit as much as 20% variation within a species with respect to geographic locality and time of the nesting season. There is also considerable local variation, irrespective of season and locality, which is related to nutrition and perhaps to an inherited variability. The application of curve-fitting as a method of analysing intraspecific variation is discussed briefly, and the importance of comparative growth studies is emphasized.

Growth patterns are correlated with other parameters of the life-history to evaluate the extent of diversity in the course of growth. Low rates of growth and prolonged growth periods occur primarily in species large for their families and in oceanic species. In most others, high rates of growth are maintained for longer periods of time. The shape of the growth curve is not related to the mode of development (i.e. whether precocial or altricial).

Overall relative, or weight-specific growth rates, as measured by the constants of fitted growth equations, are most highly correlated with the adult body size of the species, changing as the -0–278 power of adult body weight. Smaller variations in the rate of growth appear to be correlated with differences in nesting success; open-nesting passerines grow faster than hole-nesting species of a similar size. Growth rate is further correlated with brood size. Oceanic species with single egg clutches and tropical land-birds with small clutches have low growth rates.

The asymptote of the growth curve of the young (in relation to the adult weight) is related to the foraging behaviour of the adults. Aerial feeders generally have high asymptotes while those of ground feeding species are usually below adult weight. These differences are related to the need in the former for well-developed flight at the time of fledging.

The diversity of growth patterns is related to evolutionary trends which are the result of (1) selective forces acting at stages of the life-history cycle other than development, (2) factors which affect the survival of offspring during the growth period, and (3) adjustments made to balance the energy budget of the family group. The last trend is discussed in detail in relation to the correlations found in the analysis. Two hypotheses are presented. Firstly, in species which cannot gather enough food to support even one young at a normal growth rate, the pace of development is reduced to decrease the energetic requirements of the young. Secondly, in species with small clutches, where adjustments to feeding capacities are not readily made by changing brood size, growth rate may be adjusted to accomplish this. The lack of critical energetic data to test these hypotheses is emphasized as a major deficiency in our understanding of the breeding biology of birds.

Patterns of growth in birds

Existing and emerging pathogens pose unusual challenges for conservation because of their potential to drive rapid changes in the numerical abundance and genetic composition of wild host populations. An increasing number of studies indicate that host genetic diversity plays an important role in buffering populations against widespread epidemics, and that parasites represent powerful selective agents in natural populations. The observation that infectious diseases might be both mitigated by and rapidly change the genetic composition of host populations gives new significance to the role of host genetic diversity in species conservation. Less clear is the role that pathogen evolutionary change plays in the emergence and spread of new diseases, but recent examples indicate that humans might be selecting unknowingly for rapid changes in pathogen biology through habitat fragmentation, climate shifts and environmental pollution. Although the risks they pose to endangered species are apparent, pathogens and other natural enemies can be a driving force behind species and genetic diversity in natural populations, and preserving interacting networks of coevolving populations should enable hosts to respond better to future disease threats.

Rapid evolutionary dynamics and disease threats to biodiversity

This analysis uses information obtained primarily from museum collections to estimate demographic parameters of populations of thrushes (Turdus spp.) from through- out the Western Hemisphere. Adult survival rates were estimated from the proportions of individuals >1 yr old in museum collections, assuming constant population size, discrete reproductive seasons, unbiased collecting, and maturity at 1 yr old. The effects of relaxing each of these assumptions were examined. The resulting biases were found to be small compared to differences between populations, and in several cases, they were opposite to the conventional wisdom that survival rate increases towards the equator. The annual survival rate of adults (S) is estimated without bias by E(S) = A/(A + I), which has a standard error of ((AI)I(A + J)3), where A is the number of adults in a collection and I is the number of immatures. In Turdus, adult and immature birds can be distinguished by the appearance of the secondary coverts, the immature forms of which are retained until the first postnuptial molt at - 1 yr old. The present analysis included 8653 specimens from 30 populations of 19 species from Alaska to southern Patagonia. Additional data tabulated from museum specimens included numbers of juveniles, evidence of breeding, worn plum- age, and molt. Estimated annual survival rates varied from a mean of 0.56 in temperate North American populations, to 0.68 in subtropical South American populations, 0.76 in lowland tropical populations, and 0.80 and 0.85 in tropical montane populations in Central and South Amer- ica, respectively. Samples of adults and immatures restricted to the period immediately prior to the breeding season gave results that were indistinguishable from samples summed over the entire year. Survival rate was most strongly correlated with the difference between maximum and minimum mean monthly temperatures (r = -0.84). Thus, survival is in- versely related to seasonality of temperature. An index to fecundity (J) was estimated by the frequency of juvenile specimens (gen- erally <2 mo old) relative to those of adults in museum collections. This index was inversely related to annual adult survival. A relative index of prereproductive (generally lst-yr) survival (Sa) was calculated as the annual adult mortality (1 - E(S)) divided by J. Estimated Sa was independent of estimated S. Calculations of annual fecundity (F) from field studies on breeding of selected species supported both of these observations. These results, which are consistent with conclusions based upon broader comparisons among birds, suggest several hypotheses: (1) adult survival in Turdus populations is de- termined by physical conditions during the nonbreeding season, particularly various eco- logical effects of low temperature; (2) fecundity is sensitive to density-dependent feedbacks from adult population size and, possibly, to environmental factors correlated with other factors that independently affect adult survival; and (3) lst-yr survival, age at maturity, or both, also are affected by density-dependent factors.

/pdf/comparative-demography-of-new-world-populations-of-thrushes-pia0bqeipq.pdf

Comparative demography of new world populations of thrushes (turdus spp.)

We analyzed mitochondrial-DNA (mtDNA) restriction-site variation in pop- ulations (subspecies) of the Streaked Saltator (Saltator albicollis) in Panama, Peru, and the Lesser Antilles. Genetic differentiation between populations (Panama vs. Peru, 0.035; Lesser Antilles vs. Panama/Peru, 0.063) greatly exceeded values reported for populations or sub- species within North American bird species (0.0028-0.0086), and was near the high end of the range reported for congeneric species of passerine birds (0.016-0.073). Nucleotide di- versity within populations was similar to that reported for other species of passerines and did not differ markedly between mainland and island populations. Thus, founder effects and population bottlenecks associated with island colonization appear to have caused little, if any, loss of mtDNA nucleotide diversity. No significant mtDNA differentiation was observed between populations of named subspecies on mainland Panama (S. a. isthmicus) and the Pearl Islands (speratus), or between two subspecies in the Lesser Antilles (albicollis and guadelupensis). Saltator albicollis exhibits marked geographical genetic differentiation, as assayed by mtDNA polymorphism, but this bears little relationship to subspecies distinctions. Finally, the genetic data suggest that Antillean populations of Streaked Saltators should be distinguished at specific rank (S. albicollis), with continental forms referred to S. striatipectus. Received 7 May 1992, accepted 14 August 1992.

Tropical passerine, the streaked saltator (saltator albicollis)

Patterns of parasitism in insular avian communities can provide insight into processes that maintain host-parasite associations. On one hand, replicable relationships within evolutionarily independent communities of the same host and parasite taxa would indicate that these interactions are stable over time. On the other hand, unique ecological conditions on each island, sporadic colonizations and extinctions, plus new genetic variation would lead to island-specific host-parasite relationships. We examined the distribution of three parasitic taxa among avian host species on three islands in the Lesser Antilles: St. Lucia, Martinique, and Dominica. Blood protozoa of the genus Haemoproteus were found in 34% of host individuals examined. A significant species effect, but no significant island effect, was observed, suggesting an ecologically stable and replicable host-parasite asso- ciation. Cysts of the tissue-dwelling protozoan genus Sarcocystis were observed in 4% (9% on Dominica) of host individuals and were significantly associated with ground foraging. Epithelial lesions characteristic of avian papilloma virus were recorded in 4% of host individuals on Martinique only. The pattern of infection with papilloma virus or Sarcocystis (significant island effect) indicated that host species on a particular island are linked in transmission webs of these parasites. Such island-specific associations suggest a role for either history or unique local ecology in host-parasite associations. There was a statistically significant interaction between island and species effects in the prevalence of Haemoproteus. This may stem from the independent evolution of host- parasite interactions in the different island populations. We were able to assess the extent of genetic divergence of the host species by analysis of mitochondrial ATPase 6,8 sequences. There was little genetic divergence between island populations of the host species. There- fore, the variation in Haemoproteus prevalence is not likely to be related to genetic dif- ferentiation of the host populations. Birds infected with Haemoproteus exhibited elevated leukocyte levels indicative of immunological control of the parasite. After statistically controlling for the intensity of Haemoproteus infection and host species, leukocyte levels varied significantly among is- lands on which the host resided. This is consistent with the idea that insular avian com- munities are linked by transmission webs of parasites having broad host specificity.

/pdf/island-and-taxon-effects-in-parasitism-and-resistance-of-517dty5k7p.pdf

Island and taxon effects in parasitism and resistance of lesser antillean birds

On the limitation of brood size in passerine birds by the ability of adults to nourish their young.

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Comparative demography of new world populations of thrushes (turdus spp.)

Tropical passerine, the streaked saltator (saltator albicollis)

Island and taxon effects in parasitism and resistance of lesser antillean birds

On the limitation of brood size in passerine birds by the ability of adults to nourish their young.