Final Exam Flashcards
Why are there so many types of fruits and dispersal patterns in plants?
To overcome herbivory and various evolutionary adaptations of herbivores to (directly or indirectly) reduce dispersal. Herboviory affects all stages of the life history, but critical to the reproductive ability of a plant is the fruit/seeds an the ability for them to disperse. Many dispersal strategies of plants are dependent on the ‘right’ environmental conditions for that specific sp.
The patterns of seed dispersal are determined in large part by the dispersal mechanism and this has important implications for the demographic and genetic structure of plant populations, as well as migration patterns and species interactions. There are five main modes of seed dispersal: gravity, wind, ballistic, water, and by animals. Some plants are serotinous and only disperse their seeds in response to an environmental stimulus.
i.e. many Australian native seeds are hard or covered in impenetrable coatings to make them unappealing as a food source, and require fire to ‘crack’ the seed and allow it to germinate.
Seed dispersal is likely to have several benefits for plant species. First, seed survival is often higher away from the parent plant. This higher survival may result from the actions of density-dependent seed and seedling predators and pathogens, which often target the high concentrations of seeds beneath adults. Competition with adult plants may also be lower when seeds are transported away from their parent.
answer W1L1 - Herbivory & dispersal success
Explain the difference between inducible and structural defences, provide examples of each and discuss their benefits and disadvantages for the plant.
The co-evolution of plants and animals has meant that plants have evolved many diverse mechanisms to cope with herbivory. Such defences include concentrations of toxins that can be classified into structural and inducible. Structural refers to permanent, constitutive defences present at a stable concentration in the plant. The perception of attack triggers the synthesis chemical or structure (inducible defense).
Benefits:
Reduced chance of herbivore adapting to plant defences as inducible defenses cause variation in defense constituents of a plant - make the plant more unpredictable environment for insect/ herbivore.
• Example: herbivory on radish by cabbage looper caterpillar demonstrated that the increase of defence chemical concentration= significant decrease of pupation rates. Therefore a plant that produces variable concentrations of defence chemicals is better defended than one this is producing only mean levels of toxin x.
Disadvantages:
High cost involved with stimulation/synthesis of toxin In absence of herbivores. Allocation away from fitness-relevant process such as growth and reproduction.
• Example: herbivory on broadleaf dock by green dock beetle induces an increase in cell-wall bound peroxidase. The re-allocation of resources reduces growth of new leaves and root expansion.
If a plant is highly likely to be encountered by a herbivore, plant will invest more resources in synthesis of broadly effective defences and will therefore have an increased concentration of toxin x. For plants that are rare and less likely to be encountered by herbivore this is a poor strategy and will therefore invest less resources in synthesis of toxin x.
Explain the phenomenon of the so-called “talking trees” and discuss the evidence that supports it.
BROADLY: trees increase production of secondary compounds when exposed to damaged trees.
Exposure to herbivory induces synthesis of defence mechanisms (chemical or morphological). In the case of ‘talking trees’, trees neighbouring damaged trees induce the synthesis of secondary compounds (phenolics) although they themselves are undamaged.
e.g. Acacia trees- some subjected to pest outbreak, after initial outbreak insects spread to neighboring trees however it was found that after initial outbreak the damage by pests was stronger upwind than downwind. Once tested it was found that trees downwind had increased concentration of tannins, suggesting that trees could use chemical signals that dissolved in the air to warn of herbivory.
Studies strongly suggest that when damaged the plant produces volatile compounds which is picked up by the environment (air or water e.g. algae) and perceived by neighbouring plant.
-from an evolutionary perspective- this could be considered a kind selection, in that the trees selecting relatives favouring own genes.
-BUT NO- because even competing species respond, which suggests that the production of a signal is not an evolutionary adaption. A more restrained/logical suggestion however, is that plants have evolved the ability to detect chemicals in the environment that indicate the presence of herbivores.
answer W1L2
Grazing in arid lands around has complex effects on soils and vegetation. Provide a diagram showing the connections between those effects and discuss how this interconnectedness affect the possibility of recovery of overgrazed rangelands.
answer W2L2
a) Explain how the behaviour of herbivores can evolve to avoid some of the effects of toxic plant compounds. Provide two examples. /Discuss the following statement and provide examples to illustrate your argument: “The coevolution of herbivores and plants has on occasion allowed the animals to take advantages of the defences evolved by plants to increase their own fitness”.
b) Explain why the evolutionary adaptation of herbivores to the nutritional and defensive characters of plants often leads to specialised diets in insects but rarely so in mammals.
a) The typical response from herbivory in plants = as intensity of herbivory increases, plant performance decreases. Herbivory is a strong selective pressure as it affects every stage of a plant’s life history, therefore plants have (continually) evolved defence mechanisms including:
1. Chemical (phenolics(tannins), toxins (n based compounds), allergenics)
2. Morphological (thick/tough leaves, spines, hairs, resin/latex production)
There are two methods of adaptation/evolution in herbivores to either avoid the effects of toxic plant compounds, or to take advantage of the plant’s defenses to increase their own fitness. An example of the former is some non-specialist herbivores can consume particular toxic species until reaching their toxicity threshold (critical level in bloodstream) beyond which causes a negative effect. The animal then moves to next species and accumulates different toxic component while previous component is broken down by liver, and to a lesser degree, kidneys. This behavioural strategy is adopted by possums in eucalypt forests. (Mammals learn and move on…insects dont and therefore must become specialised)
An example of the latter is monarch butterfly larvae - evolved behaviour in which it can locate high pressure latex tubule in plant. If larvae was to try and consume the latex would ‘glue’ mandibles. Therefore evolved behaviour includes making small incisions in plant to drain latex and is then able to consume safely.
Evolutionary Response of Animals:
Avoidance ( ie. aphids digestive tract adapted so high concentrations of carbohydrates are not present for an extended amount of time and are therefore not absorbed at a high rate)
Detoxification (specific enzyme inhibitors)
Accumulation (accumulate toxins but relocate to areas that do not interfere with physiological processes (ie. fat tissue) - an example of this is monarch butterfly accumulates toxins in fat cells, and re-allocates them to their wing tissue - wings are then poisonous)
Fast processing- quick excretion: the tabacco leaf catepillar sucks H2O and sugars from plant phloem, but gets too many carbs, so has specialised digestive system that allows for a lg part of the sugars and H2O to circumvent the digestive system, while concentrated amino acids and some sugars go thru the main digestive pathway = v. efficient absorption.
b) Several reasons; firstly the difference between the evolutionary time scale of generations between insects & mammals is huge. Insects can have a turnover of generations that are tens of times faster than mammals and therefore; this allows for specialisation and adaptation to their surroundings at a rate significantly faster than any mammal. They can also clear toxins faster due to lack of liver (mammals require complex enzymes for detox.)
Discuss the mechanisms through which grazing can increase the productivity of ecosystems. Provide examples.
Grazing has a complex effect on the productivity of ecosystems because on one hand it has the potential to degrade the productivity of an ecosystem, but there are also many mechanisms through which is can increase the productivity.
An increaser plant sp. is one that can tolerate herbivory, and in doing so over-compensates as a result defoliation, investing resources to increase their numbers as decreaser plants are reduced.
(Decreaser plants are the first plants to die out under continued heavy grazing. These plants decrease because they are either quite palatable and sought out by grazing animals or they lack physiological attributes that help them recover from grazing). Many increaser plants avoid grazing damage because they grow close to the ground, or are less palatable than decreasers. Increasers often also possess physiological mechanisms that help them recover from grazing.
GRAZING EXAMPLE: a system where the dominant species is more palatable- some level of grazing of this dominant species(at least proportionally to their abundance) then the system will increase in diversity. Mechanisms:
- reduce in pop of dominant sp. - enables niche partitioning to competing species
Changes in the soil composition: arid land example- destruction of crust that binds particles on surface of the soil breaks down mosses and algae which opens niche for dispersing seeds or emergence from beneath soil crust.
Several models have been developed to explain how so many species coexist in biological communities. Select two of the models presented in lectures and discuss their similarities and differences.
(This has been asked in both 2014 and 2012 exam)
Models explaining coexistence in community structure are either based on equilibrium or non equilibrium.
Equilibrium models include niche differentiation and partitioning, the Monod-Tilman model and ecological equivalence. Non-equilibrium models are the Hutchinson-Hubert species dynamic, Intermediate disturbance (Connell-Huston), Connell-Jansen seed and seedling, and the storage effect hypothesis (Chesson). CHOOSE ANY 2 OF THESE
Eg. Intermediate disturbance and storage effect hypothesis:
They are both non-equilibrium based, meaning they treat ecosystems as inherently dynamic and evolving. They both involve changes to community structure brought about by punctuated events, but the dynamics of species in the intermediate disturbance hypothesis synchronised by a disturbance resetting the playing field and allowing r-selected species to increase. Disturbance prevents competitive exclusion and therefore doesn’t allow for domination by K-selected species. This also promotes diversity. At a certain point between r & K selected species you will probably have the highest level of diversity and stability in the system, but it is never constant. Continuously changing ^^.
In contrast, the abundance of species in the storage effect model are not synced, but rather separated in time based on each species’ preferred conditions for reproduction and recruitment. DENSITY DEPENDENT and includes random variation in environmental conditions. Species will do better depending on the suitability of the year for their own fitness…some years will be good for this species and other years for the other species. e.g. the soil-seed bank with perennial plants in the desert. In the good years, different species will have a significant advantage over others and can produce a much higher abundance of offspring. BUT, according to density dependant hypothesis, the amount of seeds that the plant actually produces is the relatively same because of intra-specific competition. Then there is also inter-specific competition between the other plants. SO a combination of these effects and the non-linear variation of environmental conditions result in a continuous and relatively balanced ecosystem of co-existence.
answer W1L2
It has been argued that ecological systems are intrinsically complex. Discuss two mechanisms that could lead to ecological complexity and provide examples to illustrate your discussion.
Trophic cascades occur when predators in a food web suppress the abundance or alter the behavior of their prey, thereby releasing the next lower trophic level from predation (or herbivory if the intermediate trophic level is a herbivore). For example, if the abundance of large piscivorous fish is increased in a lake, the abundance of their prey, smaller fish that eat zooplankton, should decrease. The resulting increase in zooplankton should, in turn, cause the biomass of its prey, phytoplankton, to decrease. Trophic cascades may also be important for understanding the effects of removing top predators from food webs, as humans have done in many places through hunting and fishing activities.
INDIRECT EFFECTS - which relates to intermediate number systems. You can’t just look at the behaviour of an animal and make a generalisation without considering multiple interactions of cause and effects. FOR EXAMPLE - Darwin observed more bumblebees around towns. This was caused by the introduction of cats who controlled mice who predate on bumblebee nests. Furthermore, bumblebees are important for the pollination and therefore cats are indirectly affecting pollination… This is a relatively simply ADDITIVE model whereby adding up the effects of cat effects on mice AND mice effects on bumblebees you can measure the observed effect. Known as CHAIN INDIRECT EFFECT. (Sp. C changes the abundance of Sp. A)
More complex is Interaction modification effect. In the chain indirect model the changes in abundance of species is the main factor that is measurable. However in the interaction model, the intensity of these interactions with other organisms has the most weighting and cannot be measured with reductionist approaches…much harder to predict and quantify.
Spatial heterogeneity;
A property generally ascribed to a landscape or to a population. It refers to the uneven distribution of various concentrations of each species within an area. A landscape with spatial heterogeneity has a mix of concentrations of multiple species of plants or animals (biological), or of terrain formations (geological), or environmental characteristics (e.g. rainfall, temperature, wind) filling its area. Environments with a wide variety of habitats such as different topographies, soil types, and climates are able to accommodate a greater amount of species. The leading scientific explanation for this is that when organisms can finely subdivide a landscape into unique suitable habitats, more species can coexist in a landscape without competition, a phenomenon termed “niche partitioning.”
Several hypotheses have been developed to explain why some species are aggressively invasive when introduced into a new environment. Select and explain three of the hypotheses discussed in lectures.
Gaps in resources used exploited by invader
•Newly opened gaps in resource use allows invasion. Similar to other theories but more emphasis on gap creation due to various impacts/changes on system. These include: changes in land use reducing the abundance of native species, introduction of new disturbance regime freeing up resources, increased resource base (eg. runoff of fertilisers, effluents etc.), & climate change.
•This theory accepts the ‘empty niche’ idea and assumes that there are unused resources (which is often the case in low diversity ecosystems). **NB. Only a resource space can be empty. A niche is a property of the species.
Greater reproductive capacity:
•Invaders are more likely to be r selected (poorly supported)
•Invaders may benefit from novel disturbances that either free up resources, lower damage by herbivores or parasites, or allow access to mroe resources.
Poorly adapted native species
•Especially in a rapidly changing environment, invaders may be better adapted to habitats than the endemic native species. For example, recent evolution of Mediterranean condition in Aus. has enabled some invasive species to adapt better (eg. Olives).
Escape from enemies
•Introduced species have no predators or parasites in the invaded area. Recent review of evidence showed little support for this theory but it is probably true in cases where species are controlled by specialist herbivores or pathogens.
However, in many cases native species have evolved tolerance or protection against co-evolved enemies (predators/parasites) and introduced species may lack such adaptations. In these cases, plant parasites may have more negative effects on invading species.
Explain the concept of indirect effect and provide one example where their understanding is important for the management of an ecological system.
INDIRECT EFFECTS - which relates to intermediate number systems. You can’t just look at the behaviour of an animal and make a generalisation without considering multiple interactions of cause and effects. Also CHAIN INDIRECT EFFECT. (Sp. C changes the abundance of Sp. A).
The example of feral goat and pig eradication in Pacific Islands. They thought that by removing these animals this would release predation pressure on the native vegetation. WRONG. As well as controlling the native species, they were controlling an exotic vine that was barely noticeable. After removing the goats and pigs the exotic vine went crazy and overran the native species….
Important for management of ecological systems BECAUSE it is imperative to know what the indirect effects may be of the actions you undertake. For crop farmers this is really important as this is money & food.
Example - Corn growing in Nicaragua. Pesticides weren’t that readily used until they became widespread and commercially available (cheap). Farmers use the pesticide because caterpillars were eating a large amount of their crops! BUT INDIRECT EFFECTS MUAHAHHAHA. After applying the pesticide they saw that they had more damage to the corn. WHY? Well it turns out that predatory ants played an integral role to controlling caterpillar populations, and so on using the pesticide they affected both caterpillars and ants. The ants were having an INDIRECT positive effect on corn yield. So even though the pesticide would have succeeded in deterring many caterpillars which would = positive effect on corn production, it was actually NEGATIVE overall :(
answer W3L1
Discuss the importance of temporal effects (e.g. time lags, or priority effects) on ecosystem functioning and provide one example where their understanding is important for the management of an ecological system.
A time lag (usually just called “lag”) in a population occurs when the population responds to an independent variable, but not right away. A lag delays a response. If the lag is increased, the response delay will be increased.
Delayed density dependent effects on population growth -
Theoretically a lag in the response of a population control to a cue results in cycles of population size with time i.e. abundant food in one year would result in increases in the birth rates the following year in mammalian herbivores and carnivores; likewise lower food availability would have a delayed response due to an animals ability to store energy as fat deposits, which can also dampen cycles relative to a situation where food is not stored. Similar feedbacks might exist between predator and prey populations through delayed effects of birth and death rates on population sizes
Research indicates multiple factors contribute to population cycling through delayed density dependence.
A priority effect is the impact that a particular species can have on community development due to prior arrival at a site.
There are two basic types of priority effect: inhibitory priority effects occur when a species that arrives first at a site negatively impacts a species that arrives later by reducing the availability of space or resources. Facilitative priority effects occur when a species that arrives first at a site alters abiotic or biotic conditions in ways that positively impact a species arriving later. Priority effects are a central and pervasive element of ecological community development. These effects have important implications for natural systems as well as ecological restoration efforts
Using an example, explain what is meant by the phrase “paradox of invasion”.
The paradox of invasion is not really a paradox as there are explanations for most invasion events by exotic species. It questions how a species can become a pest when it should perform best in its native range. This is based on Darwinian evolution where a species is a direct product of its history of environments and thus it should be perfectly adapted to its home range. Yet, we see species such as the brushtail possum having its distribution in its home range (Oz) dramatically reduced while it is proliferating as a pest in New Zealand.
This is partly due to the suitability of the climate and the dietary availability of NZ plants that are part of the gondwanan vegetation evolution (same as the food source in its native Aus. minus the defence mechanisms, and with increased palatability —>now changed by possums who have changed the palatability of native flora). A major factor that often allows the spread of invasive species is the lack of their natural predator in their new habitat, as well as lacking any pathogens that may have been present in their native/home range. This can lead to local adaptation, where able to put more effort into seed mass (to proliferate) rather than in thickening the cell wall (a necessary adaption in its native range as a result of grazing pressure). No grazing in new lox and therefore able to decrease defense & invest in reproduction…ths increasing success.
Using an example, explain what is meant if a taxon is described as an “evolutionary relict”.
Using examples, explain the difference between taxa that are ‘evolutionary’ versus ‘climatic’ relicts.
Evolutionary relicts are species that were once dominant as resource competitors but were not able to compete with newer lifeforms that evolved at a faster rate and in a more beneficial direction. This is usually due to the life history characteristics of the species being more beneficial in previous environments dominated by different biota. An example of this is the past distribution evidence of magnolias, considered to be one of the most primative families of flowering plant groups. Its showy flowers are attractive to insects, and at one time they occupied a wide belt across the tropical, sub-tropical, and temperate regions of the earth for perhaps as much as 70mya. In the last 2mya they have succumbed under the pressure of fast-growing tree sp, and are now naturally endemic only to very small regions in SE Asia and some parts of north and central America.
Sometimes referred to as glacial relicts, climatic relicts are taxa that were more widely distributed in the past when climatic conditions were more conducive to a greater range. During times of optimum climatic conditions, taxa may expand their ranges into new regions. As global climates have changed, or are restricted by changes in glaciations or sea level rise, or by geologic separation due to plate tectonics, climatic relict taxa have adapted by reducing their ranges to smaller refugia, where residual communities remain isolated (or disjunct) from their ancestral community. An example is Nothofagus Antarctic Beech trees once widespread on Gondwana - Antarctica, Australia etc, but now confined to cool wet locations in Tasmania, New Zealand, & Chile.
Define what is meant by an ‘ecological niche’. Compare and contrast the types (i.e. concepts) of ecological niche used by ecologists. How is the niche concept relevant to species distribution modelling? Provide examples to illustrate your points.(W7)
Where a sp. lives
what space it occupies in the landscape
what it does (i.e. how it interacts with the local environment)
Within the envrionment, the range of conditions, resource levels and species densities affect the:
Reproduction
Survival
Growth of the sp.
Environmental factors include temperature, pH, toxins/chemicals pollutants/radiation, and salinity/micronutrients. These factors require a sp. to adapt behaviourally, physiologally or morphologically in order to peresist in the environment.
Recess/Role niche:
The ecological meaning of niche comes from the meaning of niche as a recess in a wall for a statue. i.e an ‘empty niche waiting to be filled’ and a ‘cubby hole a sp. fits into’ determined by habitat characteristics and types of food. Well associated with physiological, morphological, and behavioural adaptations.
e.g. there are sp. that are hugely spatially separated and yet very similar in the niche they occupy and their adaptations (ecological equivalents), an example being the different hopping mice that have evolved in Australia (Spinifex Hopping Mouse) And Africa (Saharan Jerboa). This concept is based on the idea that the niche exists independently of the organism, and does not consider interactions between sp. which is crucial in modern ecology and to omit this is highly unrealistic.
Population-persistence niche:
This concept allows quantitative characterisation of ecological niches and focuses on the species of interest itself, rather than an open opportunity/recess. A niche is a quantitative description of the n-dimensional hypervolume that allow the persistence of a local population. The dimensions are environmental conditions and resources, that define the requirements of an individual or a species to persist. The “hypervolume” defines the multi-dimensional space of resources (e.g., light, nutrients, structure, etc.) available to (and specifically used by) organisms. The range of persistence boundaries highlight the adaptability and resilience of a population faced with a changing environment. It also insinuates that no niche is unoccupied.
It also divides niches into two categories:
1. Fundamental niche: the largest ecological niche where an organism/species can persist in absence of interspecific competition and predation. (note. persistence = non-negative population growth).
2. Realized niche: the proportion of potential (fundamental) niche occupied by a species when competitors/predators are present. Ie. the portion of niche not overlapping the fundamental niche of competing species PLUS the overlapping portion where the given species can still persist.
Compared to the recess/role niche concept, it is hard to discover/define a niche due to n-dimensions (ie. non-comparable, and with an arbitrary number of dimensions, eg. resource availability, condition, density etc.), assumes no feedback from other species, and focuses on competition (excluding other interactions). difficult to apply empirically because it requires measuring “r” (intrinsic growth rate) in a n-dimensional space.
Resource-Utilisation
a niche is a quantitative and multi-dimensional description of RESOURCE USE. Therefore, the relative use of a resource is quantified by the frequency distribution along a niche axis. This concept describes a species’ natural history, broadly classified as habitat, food type and activity time (behaviour). This reduces the need to identify environmental variables as averages and assumes nothing about pre-existing niche recesses, ecological equivalents or empty niches. Under this concept, species that are too similar in resource requirements cannot coexist and similarity is expressed as niche location proximity (along an axis) and niche width (ie. generalists have large niche width).
Environmental Niche Modelling
The niche concept enables species distribution modelling by combining elements from all three niche concepts. Modelling characterises an environmental-niche as a function of multivariate spatial information from throughout a species’ geographic range. To predict a potential future species range of a given species we can combine information about: scale/overlaps of fundamental niches (population-persistence niche), locations with the right characteristics and absent competitors (recess/role), and niche similarity between species (overlap) (resource-utilisation).
For example, the pygmy bluetongue lizard (highly endangered and range restricted) had its species distribution estimated based on human-induced geographic range contractions. The species has specific requirements of native grasses/shrubs and the presence of burrowing spiders to provide shelter/habitat. Future habitat suitability was estimated by comparing predictions of current and future area of occupancy from plant-habitat models with environmental change models (climate).
The “Rapoport effect” is based on the observation that, particularly among North American taxa, geographic range sizes of species increases at higher latitudes, from the equator to the Northern pole. This observation has, in turn, been used as a possible mechanism for the higher species richness of different taxa within the tropics compared with the temperate zones. Discuss why the Rapoport effect is not generally well-supported by scientific studies and provide at least two alternative mechanisms for the latitudinal difference in species richness between the tropics and the temperate regions.
Global patterns of distribution of species & global relationship of abundance i.e. Latitudinal Biodiversity Gradient (W8)
Writing in the ‘Geographical Distribution of Animals’ (1876) Alfred Russell Wallace observed ‘Animal life is, on the whole, far more abundant and more varied within the tropics than in any other part of the globe, and a great number of peculiar groups are found there which never extend into temperate regions’. Discuss this observation in terms of (i) alternative explanations for the Latitudinal Biodiversity Gradient; (ii) any possible exceptions to the general observation; and (iii) the evolutionary drivers responsible for differences in species richness between the temperate and tropical regions.
answer W8 (Rapaport effect W7L2) There are several studies that have demosntrated why the Rapoport Effectis not a valid mechanism for species richness across varying latitudes.
The range size of new world birds was investigated, and it was found that the majority of species with the smallest ranges lived about 17°North of the equator. This latitude was not the smallest land area in North America. It lies at the point of vegetative transition between grassland and the mid atlantic forests where biogeographic and floristic change form a thin band of very rare and specialisation requiring habitat. Thus, birds that inhabit the band are adapted to environmental conditions not found outside this band and have very small range sizes (habitat specialists). When people have looked outside of the Americas, they have struggled to find a similarity between climatic variability and range size. This is possibly because it is locally specific to the Americas.
Australian Eucalypt species had their distributions studied, the majority of which had very small distributions with only 6% of species covering more than 1% of Australia. There is no latitudinal pattern between distribution, where the largest range sizes are close to the widest region of land but slightly offset because the widest point of Australia does not have the highest habitability compared to other latitudes. Species richness also does not follow this pattern, it is greatest in the biodiversity hotspot region of old, geologically stable environments in South West WA.
Species have to be able to survive a high range of extremes, thus higher latitude species that are prone to greater seasonal variation must be able to adapt to larger range behaviour. Seasonal variation and differences between minimum and maximum temperatures are not 100% predicted by latitude and depend on many other factors (geological structures, proximity to oceans etc.)
Ranging behaviours may also be inherited, indicating a relationship between phylogenetic groups and range size. This was tested in birds by first taking sister species and dividing the smaller range by the larger range of each species. Range size pairs were significantly more different than expected by chance. To further prove this, researchers found 41 independent phylogenies of species and tested the correlation of range size against the phylogenetic relations between species. They found that range sizes are probably dynamic and have no relation to evolutionary history. It is probably more to do with how organisms utilise resources that affects their range size, and although this is slightly related to equatorial proximity (higher energy = easier nutrient/energy access) there are too many exceptions to use latitude as an accurate indicator of species richness.
Exceptions to the observation:
New world birds (Americas)- have their smallest range size at 17°North
Many freshwater fish have very small range sizes at high latitudes (because water body size directly impacts range and many lakes are isolated).
Bony fish have highest species richness just south of the equator (thus smallest range size)
For a difference in species richness to occur there must be something affecting both the rate of change in species and the extinction rate (evolutions trade-off of speciation and extinction).
