This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.
The interaction between two species is based on the context of consumer-resource interaction, and it is primarily determined by density effects. Most of the indirect interactions are considered to be through series of direct interactions. The resulting indirect effects can be mediated by either change in the density or change in the traits. In the case of Density mediated indirect effects, Species 1 or predator causes change in the density of species 2 or prey1, which then results in the increase in abundance of species 3 or prey2 (Dr McEuen, Lecture notes 2010). Such effects are commonly seen in trophic cascade or predator-prey interactions. For example starfish in intertidal zone causes increase in the diversity and density of algal and invertebrates upon holding mussels and barnacles in check (Dr McEuen, Lecture notes 2010). The effect of such checks influences positive indirect effect on other preys (Dr McEuen, Lecture notes 2010). Another example illustrates the change in the trophic cascade by top predator. In the presence of top carnivore Orca, density of sea otters gets directly affected and Sea urichins abundance increases indirectly (Dr McEuen, Lecture notes 2010). This tells us that cascading effects can always lead to density mediated indirect effects (Dr McEuen, Lecture notes 2010). However not all indirect effects are mediated by changes through abundance or density, rather it could be based on trait mediated too (Dr McEuen, Lecture notes 2010). Trait mediated indirect effects can be defined by change in the traits of species 2 caused by species 1 affecting the species 3, in other words herbivore 1 causes increase in secondary compounds in plants which negatively affects the growth of herbivore 2 (Dr McEuen, Lecture notes 2010) . For example Spittlebug which is a specialist herbivore on the willow incurs mechanical damage by laying eggs in the distal part of willow. The compensatory shoot growth produces greater number of leaves and causes increase in the density of 23 leaf rolling caterpillar species (Dr McEuen, Lecture notes 2010; Ohgushi, 2005). After the formation of rolled leafs by cater pillars, most of the insects particularly aphids gets colonized and their habitat increases because of their specialist in utilizing leaf rolls (Dr McEuen, Lecture notes 2010; Ohgushi, 2005). Increase in aphids increased aphid-tending ants and these ants decreased the bettle larvae survival (Dr McEuen, Lecture notes 2010; Ohgushi, 2005). Another example demonstrated that early feeding of tiger moth on bush lupine leaves will negatively affect the larval growth of tussock moth when they feed on same leaves (Dr McEuen, Lecture notes 2010; Ohgushi, 2005). This might be due to decreased nitrogen caused by early herbivory tiger moth could have affected the leaves suitability for tussock moth (Ohgushi, 2005). Based on the Ohugushi's paper, the comparison shown in the table 2 demonstrated that most of plant-herbivore interactions lead to trait mediated indirect effects while herbivore-predator interactions lead to density mediated indirect effects (Ohgushi, 2005). Furthermore within trophic interactions trait-mediated indirect effects are less frequent but more common in nontrophic interactions while density mediated indirects are more common in trophic cascade than in non trophic interactions (Ohgushi, 2005).
2. Regime shifts and Ecosystem Resilience
Current ecosystems in the earth face lot of uncertainties at different time scale. Variable environments and inevitable human activities challenge the desired state of ecosystem with some events and disturbances. An Ecosystem resilience can be defined as "magnitude of disturbance that a system can experience before it shifts into a different state (stability domain) with different controls on structure and function" (Folke et al, 2004; Holling, 1973). And the word resilience stands for the system that has ability to retain essential function and structure after absorbing significant disturbance and undergoing some changes. The occurrence of disturbance at all scales reflects the dynamics of ecosystem resilience and the degree of phase shift from one state to another state. The existence of such shifts in ecosystem implies shift in ecosystem system services, which is called as Regime shift. In other words it can be referred as shifting one stable to another stable state. All complex ecosystems holds critical threshold regime shift, when it crosses over, the ecosystem shifts towards different direction. For example in temperate lakes, Carpenter (2003) showed the existence of two different regimes in Lake Ecosystem. In clear water regime, phosphorous inputs, recycling from sediments and phytoplankton biomass were found to be relatively low, but when phosphorous level goes high clear water regime shifts to turbid water regime and eventually kills the fish, and reduces the efficiency of ecosystem services in lake water ecosystem. Reverting to original regime will be accounted to the disturbance of new resilient state and must cross the critical threshold to get back to the clear water lake ecosystem (Folke et al, 2004). Another example demonstrates the existence of two different plant dominated states in Lake Ecosystem. It was found that floating plants exhibit superior consumption of light and carbon than submerged plants; hence decrease in light and carbon level leads to shift in submerged dominated plants in Lake ecosystem (Folke et al, 2004). The change of conditions in submerged dominated plant state would lead to drastic effects because floating dominated plants could cause anoxic conditions and can reduce the diversity and biomass of animals in freshwater ecosystem (Folke et al, 2004). In such case nutrient controlling would be very critical in reversing the regime shift in order to restore the submerged plant dominated ecosystem state. In some cases regime shifts are highly irreversible, for example trees in the forests that survive under rainfall regime might shift their regime to long dry conditions due to low rainfall, and would eventually result in less density and would be hard to recover from such extreme regime shifts. The examples outlined in Folke et al (2004) illustrated that ecosystem resilience functions well when the system crosses over critical threshold of regime shift but not in the extreme shifts. Also the loss of resilience in an ecosystem would attribute to sudden shift in the states and less ecosystem services.
3. Functional Diversity, Species Diversity and Ecosystem services
Biodiversity in general includes the diveristy of life across different scales, like genes,species, populations,landscapes and ecosystems (Dr McEuen, Lecture notes 2010). Species diversity explains the number of species in a community or the relative abundance of individuals among species (Dr McEuen, Lecture notes 2010). Evenness in the community increases as individuals are more equally distributed. Diverse communities contribute different ecosystem services and functions in the ecosystem, and overall biodiversity acts as a base for ecosystem services (Dr McEuen, Lecture notes 2010). Ecosystem services refers to benefit to humans provided by ecosystem process in the form of goods (Dr McEuen, Lecture notes 2010). For example flood control, carbon sequestering, crop yields, sewage breakdown etc are part of ecosystem services provided to humans (Dr McEuen, Lecture notes 2010). On the other hand ecosystem function refers to process like production, decomposition, water cycling and carbon cycling. Ecosystem function could increase with increase in species richness, but sometimes species diversity might affect the ecosystem service and function (Dr McEuen, Lecture notes 2010). For example lyme disease, Borrelia burgdoferi trasmitted by ticks is found to be dominant in mice reservoir, the rate of infected ticks goes high When mammals diversity is low(Dr McEuen, Lecture notes 2010). The increase in mammal diverity affects the rate of infected ticks in the forest and subsequently the function and service (Dr McEuen, Lecture notes 2010). Similarly correlation study between microbial diversity and cellular respiration demonstrated that high species richness of aquatic microbial communities will have lower carbondioxide flux and respiration rates would increase as richness increases (Dr McEuen, Lecture notes 2010). Another example illustrated the effect of increase in leaf breakdown as diverse insect shredders are present in the leaves (Dr McEuen, Lecture notes 2010). Also the effect of nutrient cycling and mineralization was found to be occuring rapidly when the plant species diversity increased. These example tells us that species diversity does affect ecosystem function and services, and their relationship can be either linear or nonlinear (Dr McEuen, Lecture notes 2010). But most of the time species diversity acts as a insurance to ecosystem by providing greater resistance and resilience in the face of environmental changes (Dr McEuen, Lecture notes 2010). For example, high diversity of grass species in drought conditions exhibited complimentary functions that were able to tolerate drought resistance, control variation in flooding and use of different resources (Dr McEuen, Lecture notes 2010). Ecosystem with diverse species functions is considered to be more important than species diversity. Functional diversity is defined as ecosystem having all of the functions for the maintenance of its process but not all of species richness required in the ecosystem (Encyclopedia of Biodiversity). For example, Heemsbergen et al (2004) found that soil decomposition rates were primarily influenced by detritivores and not by its richness. Over all ecosystem with diverse functional groups will have less redundant but with strong functional diversity entire system will be insured against any environmental changes and their regime shift will remain stable for longer time (Dr McEuen, Lecture notes 2010). Also functional and species diversity are not always related and their ecosystem service and function will be independent of each other. Based on the reading of Folke et al (2004), it was understood that addition of single species in the ecosystem could change its structure and function and would increase the performance of ecosystem and its service. The best example shown in the paper was Myrica faya that could cause high nitrogen inputs in the ecosystem and as well as offer resistance against any major disturbances.
4. Phylogenetic tree, clade, monophyletic and paraphyletic groups.
A branching pattern of tree representing the biological lineages and evolutionary relationships among various species based on their physical and genetic characteristics is called as phylogenetic tree (Encyclopedia Evolution; Dr Vazquez, lecture notes 2010). The difference and similarity in those characteristics will represent length of the branch in a particular lineage (Encyclopedia Evolution). In order to construct a true phyologenetic tree, characters used in the analysis must be of independent and homologous (Dr Vazquez, lecture notes 2010). For example phylogeny of vertebrates based on morphological data illustrated the usage of independent characters like Vertebral column, Jaws, four walking legs, Amniotic (shelled) egg and Hair (Dr Vazquez, lecture notes 2010). Based on such characters generated cladogram suggested that outgroup Lancelet species could be due to absence of all independent characters, and other in grouped vertebrate species might be due to existence of one or more independent characters (Dr Vazquez, lecture notes 2010). Vertebrates Turtle and Leopard were found to be closely related to each other due to presence of hair character, while salamander, Tuna and Lamprey were distantly related (Dr Vazquez, lecture notes 2010). Apart from morphological data, DNA sequences are considered to be most useful data for the construction of phyologenies. For example analysis of variable DNA sites in Prunus, Daucus and Solanum suggested that Daucus and Prunus were more closely related than with Solanum (Dr Vazquez, lecture notes 2010). In a phylogenetic tree, branching group composed of ancestor and all of its descendants is called as Clade and monophyletic groups (Dr Vazquez, lecture notes 2010). For example if species 1,2 and 3 are from ancestor A, species 4 and 5 are from ancestor B, and if ancestors A and B are from ancestor C, then branch composed of ancestor C and B and its descendants species1,2 ,3, 4 and 5 is called as Clade and Monophyletic groups (Dr Vazquez, lecture notes 2010). In the case of Dacus, Prunus and Solanum phylogeny, monophyletic group will be Daucus and Prunus. Monophyletic groups are mainly supported by synamorphies (shared characters) (Dr Vazquez, lecture notes 2010). In the case of paraphyletic groups, branches will be composed of one last common ancestor and doesn't not include all of its descendants (Dr Vazquez, lecture notes 2010). For example, in clade vertebrates exclusion of birds will indicate Reptilia as a paraphyletic group (Dr Vazquez, lecture notes 2010). In some cases the reconstruction of Phylogenetic tree sometimes can be based on conflicting information, for example convergent evolution of Octopi and squid was found to be based on two kinds of eyes evolved independently within mollucs and vertebrates (Dr Vazquez, lecture notes 2010). Also reversal of DNA sequence due to back mutation might again result in conflict. Such information conflicting with the evolutionary process is called as homoplasy (Dr Vazquez, lecture notes 2010). Therefore when conflicting information are applied in phylogenetic anaylsis, it may sometime result in wrong phylogeny. In general overall construction of phylogenetic tree should involve selection of taxa, data gathering, analysis of morphological characters or DNA sequences (variable sites), Coding characters or Sequencing the information and finally use right phylogenetic method to construct appropriate tree(Dr Vazquez, lecture notes 2010). Based on the reading of Davis and Nixon (1992) paper it was understood that construction of phylogenetic tree methods could be extended as phylogenetic species concept, so as to not only study the evolutionary relationships but also could be adopted as a concept to classify certain new species based on morphological characters and categorize them accordingly in certain taxa.
Adaptation can be defined as traits that cause increase in fitness of an individual or it is a "process of genetic change of a population owing to natural selection, whereby the average state of a character becomes improved with reference to a specific function" (Futuyma, 1998; Dr Vazquez, lecture notes 2010). Adaptation can be further defined based on three important criterias: a) Design, b)natural selection and c)historical (Encyclopedia of Evolution). The first criterion is based on design where attributes that are designed for an organism survival and reproduction can function as adaptation (Encyclopedia of Evolution). For example internal structure of eye designed to form visual images, heart designed for pumping blood, and wings for flight (Encyclopedia of Evolution). Adaptation based on design criteria could be due to evolution by unconscious natural selection (Encyclopedia of Evolution). The second criterion is based on natural selection, for example birds laying fewer eggs and producing fewer offspring will survive and reproduce successively compared to birds with large clutch size(Encyclopedia of Evolution). The feeding quantity becomes larger with more chicks and sometime whole brood may starve. Hence natural selection will favor birds with optimum clutch size which can able to maximize the reproductive output or the fitness of parents (Encyclopedia of Evolution). This criterion partially overlaps with first criterion as an advantage that some designed attributes are favored by natural selection(Encyclopedia of Evolution). The third criterion is based on historical, where some attributes evolved in the past could be beneficial to some organisms and can be seen as adaptation (Encyclopedia of Evolution). For example eyes evolved from ancestral eyeless organisms have been secondarily lost. Eyeless cave-dwelling fish species evolved from ancestral eye creatures cannot be called as adaptation rather on the historical side eyeless can be called as an adaptation if it was evolved from original eyeless ancestral creatures (Encyclopedia of Evolution). Historical criterion explains certain attributes as an adaptation based on the original ancestral function (Encyclopedia of Evolution). As a result every trait in the organism cannot be considered as adaptation rather it might be due to consequences of physics or chemistry (Dr Vazquez, lecture notes 2010). For example red blood cells having red color are not an adaptation rather it is due to byproduct of hemoglobin structure (Dr Vazquez, lecture notes 2010). Some traits can be due to genetic drift than natural selection, for example cryptic pattern observed in some species may result in adaptation but it was primarily due to genetic drift (Dr Vazquez, lecture notes 2010). A similar example was seen in cain's paper, where they saw different color varieties of the shell in the snails, and it was reasoned out to be based on genetic drift and visual selectional pressure (Cain, 1989). This example demonstrated that not all traits are due to adaptation. Traits correlated with another structure cannot be called as adaptation rather it could be linked with advantageous mutation (Dr Vazquez, lecture notes 2010). Furthermore some traits may be consequence of phylogenetic history, like skull sutures in mammals. Some adaptation traits can be based on genetic makeup but over a period of time it can change its structure and function due to variations caused by environmental factors (Dr Vazquez, lecture notes 2010). For example differential size of beak depth in finches. Certain morphological traits seen in organisms can be due to environmental changes and not because of adaptation (Dr Vazquez, lecture notes 2010). In some cases combining unrelated structures might result in new adaptation, for example combination of galatosyl transferase and alpha lacta albumin produced new enzyme lactose synthase, and it found to be unique in mammals(Dr Vazquez, lecture notes 2010). Therefore it can be concluded not all traits could be treated as adaptation.
The process of reciprocal genetic change between two interacting species driven by natural selection is called as Coevolution (Futuyma, 1998; Dr Vazquez, lecture notes 2010). In other words it can be referred as reciprocal evolutionary change in ecological interacting populations. Such ecological interactions include interspecific competition, plant-herbivore, predator-prey, parasitism, mutualism and symbiosis (Dr Vazquez, lecture notes 2010). Coevolutionary process has influenced diversification in various species. There are five different modes of coevolution found in this earth based on species interactions (Dr Vazquez, lecture notes 2010). The first mode is Gene for gene coevolution based on host-parasite interactions. Both host and parasite have complementary genes that confer for resistance and virulence effects (Dr Vazquez, lecture notes 2010). Each virulence gene effect is compensated with resistant gene in the host. Not all the host-parasite interactions result in coevolutionary process, some may be due to polygenic interactions instead of Gene for gene (Dr Vazquez, lecture notes 2010). The second mode is specific coevolution where two species evolve in response to each other (Dr Vazquez, lecture notes 2010). Every change occurring in one species is countered by changes in other species (Dr Vazquez, lecture notes 2010). For example, caterpillar provides honeydew to ants, and ants fights offs predatory wasps and flies that attack caterpillars (Dr Vazquez, lecture notes 2010). The third mode is Guild coevolution which is also called as multispecies coevolution (Dr Vazquez, lecture notes 2010). It acts like specific coevolution with several species interacting each other. For example, a group of parasites interacts with group of hosts (Dr Vazquez, lecture notes 2010). The fourth mode is diversifying coevolution where reciprocal interaction between two species causes one of the species to subdivide (Dr Vazquez, lecture notes 2010). For example "Coevolution between granivorous crossbills (Loxia spp.) and conifers has been a prominent process in the diversification of crossbills" (Benkman, 2010). Another example from Ehrilch and raven (1964) paper outlined that genus Paipilo subfamily of Papilionini would feed on plant family Rutaceae and as well as on Canellaceae, Lauracea and Piperaceae. This example illustrated that coevolution has influenced expansion of feeding habitat and diversification among butterfly species. Final mode is Escape and radiate coevolution, species evolve as a defense against enemies and proliferate into diverse clade (Dr Vazquez, lecture notes 2010). Over a period of time enemies get adapted to one such defense and become specialization (Dr Vazquez, lecture notes 2010). For example herbivore Spittle bug feeding on plant willow leads to the production of secondary toxic substances from willow, such toxic metabolites released by willow defends from other herbivore insects especially leaf bugs. Over a period of time leaf bug adapts to such defenses and get diversified. One of the most common interactions leading to coevolutionary process is predator-prey interaction. For example, garter snake feeding on rough-skinned newt produces neurotoxin tetrodotoxin (TTX) at high level. Predator garter snakes exhibit some resistance to TTX within a range and preys on rough-skinned newt (Dr Vazquez, lecture notes 2010). When newt produces high level of TTX garter snakes fails to resist and might be able to prey on them (Dr Vazquez, lecture notes 2010). Another common interaction involving coevolution is plant-herbivore coevolution. For example butterly species Heliconius are said to be resistant to cyanogenic glycosides produced by Passiflora (Dr Vazquez, lecture notes 2010). The defensive compound produced by Passiflora has adapted to avoid parasitisation and the resistant to such compounds by butterflies have evolved for the tender use of foliages for laying eggs (Dr Vazquez, lecture notes 2010). Thus most of the coevolutionary process involves reciprocal effects between species interactions but not all the interaction would result in coevolution (Dr Vazquez, lecture notes 2010).
7. Primary production and secondary production
The production of organic compounds through photosynthetic and chemosynthetic process by living organisms using sunlight energy, water and atmospheric carbon dioxide is called as Primary production (Link2, Link3 and Link4). Organisms like autotrophic and lithotrophic are called as primary producers as they are responsible for primary production. Primary production primarily depends on the rate at which photosynthesis occur or the rate at which individual plant mass increases (Dr McEuen, lecture notes 2010). The amount of energy produced by primary producers gets transferred to next trophic level, where primary consumers transfer these organic molecules up the food web (Encyclopedia Biodiversity). The gross primary production produced by primary ecosystem producers gets stored in chemical energy as biomass in given length of time and lost energy through respiration results in net primary production (Link3 and link4). Overall in the ecosystem net primary production goes toward growth and reproduction of primary producers and some is consumed by primary consumers (herbivores and other animals). Primary production can be quantified as amount per per area per unit time (Dr McEuen, lecture notes 2010). Secondary production can be defined as biomass generation of heterotrophic consumers in the ecosystem (Link4). Secondary production is primarily driven by organic compounds transferred between trophic levels and when trophic levels move up production rate always declines (Link 4). Secondary production can be measured as rate or amount of biomass fixed per area per unit time because biomass is considered to be very less at a lower trophic level than in higher level (Link4, Dr McEuen, lecture notes 2010). For example algae which is said to be a primary producer gets eaten rapidly by primary consumers and their turn over is rapid, but in terms of production primary production is always greater than secondary production (Dr McEuen, lecture notes 2010).
Trophic pyramid in general represents the productivity or biomass at each trophic level in the ecosystem. In the case of inverted trophic pyramid it is the reversal projection of energy and biomass (low to high) from lower to higher trophic levels (Link2 and Link3). The disadvantage with inverted pyramids lies in the energy productivity at each trophic level because it cannot account rate of production and the turnover rate of organisms over a period of time (Link3 and Link4). The energy flow in an ecosystem cannot be compared with different ecosystems (Link2 and Link3). Also inverted pyramids are restricted to particular ecosystems like aquatic ecosystem where it can take only biomass into account and not productivity (Link3 and Link4). For example algae and phytoplankton can maintain a high "level of productivity despite being grazed by long lived fish and zooplankton" (Link2 and Link3). In such cases inverted pyramids represents will only represent the biomass number but not energy productivity at each trophic level. Also at higher trophic level only 10% of the energy is consumed to produce new biomass and at each trophic level of the pyramid roughly 10% below is represented (Wang et al, 2009). This kind of energy production cannot exist in inverted pyramids and therefore trophic pyramids can never be inverted.
Inversion depends on the type of pyramid that we are looking for. In some cases inverted biomass pyramid can be quantified same as regular biomass pyramid as grams per meter square at each trophic level. Inversion quantification can be applied only if biomass production at higher and lower trophic level biomass production is constant and low. If the turnover rate changes at each trophic level then rate of biomass production changes accordingly and inversion cannot be quantified with the base as high turnover to low turnover of next trophic level. (This question confused me lot and I am still trying to understand)
8. The importance of reconstructing phylogenies is to study the phylogenetic history of all groups of organisms in the earth. Phylogeny reconstruction further helps in retrieving certain characteristics of organisms through phylogenetic analysis. Phylogeny considers all ecological and behavioral characters for the understanding of particular evolution of traits (Dr Vazquez, lecture notes 2010). Most importantly when these characters are overlaid on phylogenetic tree evolutionary relationship among different species can be studied (Dr Vazquez, lecture notes 2010). Furthermore the reconstruction of phylogenies can answer a) Biogeographical patterns, b) character evolution, c) look for traits of interest, and d) priorities conservation ecology (Dr Vazquez, lecture notes 2010). Biogeography can be defined as distribution of biodiversity species in space and time (Dr Vazquez, lecture notes 2010). The biogeographical distribution pattern of particular species can be studied by considering the relationships among the members of taxon (Dr Vazquez, lecture notes 2010). Based on the cladistic relationship, the history of fragmentation should be able to mirror the distribution pattern of widespread taxon. For example, continental drift movement of widespread species Laurasia was found to be distributed in North America and Eurasia and Gondwanaland in India, Africa, South America and Australia (Dr Vazquez, lecture notes 2010). The taxon relationships between Pangea, Laurasia and Gondwanaland matched their vicariant events and there by phylogeny analysis was able to project the biogeographical distributional pattern (Dr Vazquez, lecture notes 2010). Character evolution is another important characteristic that can be answered by phylogenies. For example evolution of different sizes of beak among different Galapagos finches was based on difference in feeding habitat; their phyogeny study based on seed eaters, cactus flower eaters, Bud eaters and insects eaters outlined the evolution of differential beak sizes (Dr Vazquez, lecture notes 2010). Another example, phylogeny of plants among Mosses, Ferns, Gymnosperms and Angiosperms showed the evolution of embryo, xylem and phloem, wood and seeds, and flowers (Dr Vazquez, lecture notes 2010). All five characters have evolved in angiosperms with the exception of flowers in gymnosperms, and in mosses and ferns embryo and, embryo and xylem and phloem was first to be evolved in the plant species (Dr Vazquez, lecture notes 2010). Also the evolution of food preference among coevolved species can be inferred based on phylogenetic relationship (Dr Vazquez, lecture notes 2010). Looking for particular traits of interest in some species can also be answered through reconstruction of phylogenies. For example, agricultural traits of our interest can be looked in phylogentic relationship of solanum species (Dr Vazquez, lecture notes 2010). Another important ecological characteristic that can answered by phyologeny is priorities conservation biology (Dr Vazquez, lecture notes 2010). The goal of Conservation biology is to maximize species diversity by protecting extinct and endangered species. Phylogenetic analysis of diverse threatened or endangered organisms have revealed that genetically distinct lineages occur within units considered as single species (Dr Vazquez, lecture notes 2010). For example shitake mushrooms which is considered as single species was found to have four lineages based on phylogenetic analysis study. Three morphological units were recognized in those four lineages, and the conservation strategies were designed to increase the genetic diversity of single species at different locations (Dr Vazquez, lecture notes 2010). Hence phylogentic analysis provides diverse information about the extinct species lineages existence linages, and its biogeographical locations for the conservation biology (Dr Vazquez, lecture notes 2010). Although all extinct groups of organisms can't be protected, phylogenetic analysis can still be applied in identifying preserve groups than can evolve potentially (Dr Vazquez, lecture notes 2010). Overall phylogenetic analysis helps in several areas of biology, it evaluates diversity for conservation biology, provides historic context of species to determine adaptation, speciation, evolution and biogeography (Dr Vazquez, lecture notes 2010).
Lehman (2006) studied the conservation biology of Malagasy Strepsirhines through phylogenetic analysis. The results of phylogenetic analysis revealed that diversity of Malagasy Strepsirhines were present only in six biogeographic regions and their richness were significantly less when compared to other lemur diversity. Furthermore the analysis showed the taxonomic ranks of top ranked taxa and projected that lemur diversity is greatest for Daubentonia madagascariensis, Allocebus trichotis,
Lepilemur septentrionalis, Indri indri, and Mirza coquerel,but not for Malagasy Strepsirhinesi (Lehman, 2006). Based on those results regional conservational priorities of Malagasy Strepsirhines were adopted, and author predicted the need for increase and expansion of protected areas which could support the habitat of extinct species and also diversity conservation (Lehman, 2006).
9. Density dependence and its role in regulation
The change in a population density that occurs due to species interactions resulting in change in birth and death rate of that population is called as density dependence (Biodiversity Encycolpedia). As population density increases mortality rate increases and fecundity decrease (Biodiversity Encycolpedia). This could be due to intraspecific competition, interspecific competition, parasitism and predation (Biodiversity Encycolpedia). These density dependent factors regulate or control the size of population when density increases, for example female caterpillar which lays masses of eggs on virtual trees causes increase in density of young caterpillars (Link 1). As density increased massive die off of young caterpillars occurred due to finite source of food and only few completed metamorphosis (Link 1). Similarly interspecific competition is another density dependent check on the growth of a population, which could happen to due to the existence of similar ecological niche by two different species (Link 1). For example, Paramecium aurelia and Paramecium caudatum when grown in cultured medium affected each other growth rate due to food competition and increased the mortality rate of both species (Link 1). In addition to that, density dependent factors, predation and parasitism would also regulate the growth of a population by preying and causing disease on less and more successful species (Link 1). Overall density dependence factors regulate the population when the density increases. In other words when population density is high growth rate will be low.
Primary findings of the paper with regard to group size and density influencing the mortality
i. At small spatial scale (microsites) variation in mortality pattern was seen in group size alone but not in solitary and wrasse pairs. Out of 305 settlers in microsites, they found 192 were solitary, 48 in pairs and remaining 65 in groups (White and Warner, 2007). 234 groups formed by 65 wrasse species in all microsites experienced different mortality rates compared to solitary and pairs wrasse fishes (White and Warner, 2007). Based on the parsimonious maximum-likelihood model fit, results suggested that Per capita daily mortality rate decreases with increase in group size of wrasse fishes (White and Warner, 2007). From the figure 1 it clearly evidents that different group sizes of fishes on all three days at all microsites experienced different mortality rates, especially at the end of third day solitary Wrasse fish have undergone strong predation than large group wrasse fishes (White and Warner, 2007). Overall at small spatial scale (microsites) solitary and pair wrasse fishes or small group size wrasse fishes have influenced high mortality than large group size fishes (White and Warner, 2007).
ii. At large spatial scale instantaneous mortality rate increased with settler density (White and Warner, 2007). From figure 2 the pattern of mortality suggested that, increase in number of wrasse settler density per meter square increased the instantaneous mortality rate of wrasse fishes (White and Warner, 2007). Also authors found that wrasse settlement and settler mortality increased over the period of summer and the highest mortality was found in the month of august at all sites (Butler Bay, Northstar, Cane Bay and Jacks Bay) (White and Warner, 2007). No information was provided regarding the group sizes and their rate of mortality at large spatial scale. Overall at large spatial scale increased density settlers influenced the high instantaneous mortality rate (White and Warner, 2007).
Importance of scale in this study
Scale in general helps the ecologists to understand the complex phenomenon of unknown system at different scales (small and larger spatial scales). In this study scale served an important purpose for the identification of a) relationship between density and mortality rate of wrasse fishes .
b) Secondly, it helped in finding out the difference in mortality rate at different sites.
c) Thirdly, it answered the pattern of mortality rates in relation to different group sizes of wrasse fishes.
d) Fourthly, authors were able to find out the pattern of settlers in group and their microhabitat quality.
e) Finally, at large scale authors were able to show that number of settlers versus instantaneous mortality rate. Hence to study such relationships and various patterns authors have taken scale into account (White and Warner, 2007).
Scale and contradiction of grouping behavior with density dependent population via predation
The spatial pattern of settlement suggested that blue head wrasse prefers group settlement over solitary settlement (White and Warner, 2007). At this scale it was found that grouping benefits the individuals by "providing suitable habitat, less predation, assured mating patterns, safe shelter and food" (White and Warner, 2007). Furthermore it was found that grouped wrasse fishes "spend more time in feeing on plankton and grows slowly", causing predators to prey more on solitary wrasse fishes (White and Warner, 2007). Hence grouped wrasse fishes have a different habitat that makes predator less accessible to them (White and Warner, 2007).
10. Adaptive Radiation
It can be defined as single ancestral species diversifying into several forms that each species can adaptively specialized to particular environmental niche (Link 6). In other words "evolution of ecological and phenotypic diversity within a rapidly multiplying lineage" (Link 5, Wikipedia Source) which could result in speciation and evolution of divergent morphological and physiological traits in different environmental niches is called adaptive radiation. For example finches species in Galapagos island exhibit diverse beak shapes to adapt to different food sources (Link 5). Another example, cichlids in African Lake Malawi exhibited diverse feeding patterns on different prey species (Turner, 2005). Eleven cichlids found in this lake was noted to be scale eaters, fin-biters, crab eaters, removal of parasites from catfish skin, rock scrapers, sediment sifters and mouth brooders. Therefore adaptive radiation causes diversification within species and helps in maintaining similar and differential adaptations at different geographical locations (Turner, 2005).
Mechanisms promoting speciation in cichlids, and type of speciation involved in cichlids
According to Turner paper, there are three different mechanisms that promoted speciation in cichlids. Firstly, the sexual selection process leading to divergent mate preferences has caused speciation in cichlid species (Turner, 2005). Laboratory mating experiments conducted by author suggested that different forms of cichlid species exhibited non random distinct mating (Turner, 2005). Furthermore the non interbreeding of genetically compatible colored cichlid species indicated that species divergence (or speciation)have occurred due to sexual selection of divergence mate preference (Turner, 2005). This was apparently seen in one of the cichlid fishes, haplochromines, exhibiting strong differential sex characters, like parental care and strong sexual selection of male courtship traits (Turner, 2005). Also some cichlid species was found to be selecting the potential mates through using scents, sounds and movements and subsequently causing reproductive isolation (Turner, 2005). This strongly evidenced that sexual selection process could have promoted speciation in cichlid species (Turner, 2005). Secondly, author found the sympatric process of speciation occurring in cichlids speciation. Author's study of cichlids fishes in lake Barombi Mbo found that these fishes exhibited less sex role and less differentiation in breeding (Turner, 2005). This type of speciation found in some cichlids was experimentally proved through interbreeding. Author's laboratory study proved that all sympatric cichlid forms were able to produce hybrid strains and could be fertile over number of generations. The importance of sympatric speciation in cichlids species was explained more when they maintained reproductive isolation between the species (Turner, 2005). Also the molecular phylogenetic studies done by author in cichlids fishes of lake Barombi Mbo suggested that "eleven cichlid species were closely related to each other than to the whole group" (Turner, 2005) . This effectively explains that speciation in this lake could have been due to sympatric process (Turner, 2005). Thirdly, allopatric process of speciation, which is another kind of mechanism promoting speciation was found in cichlids. Over geological time, the fluctuation of water levels in larger lakes acted as a barrier for the isolation and reconnection of cichlids species, further frequent rise and fall in water level limited the gene flow in some patchy distributed habitats and restricted the species color races geographically(Turner, 2005). Such geographic barrier induced restriction caused speciation in cichlid species to exhibit assortative mating. Thus speciation causes multiple colonizations in the lakes and stimulates adaptive radiation through hybrid swarm (Turner, 2005). Also it causes novel genetic combinations among cichlids species and produces greater adaptive genetic variation (Turner, 2005). Overall sympatric and allopatric are the two types of speciation found in cichlids species.